BS5589 1989 Wood Preservation

British Standard

A single copy of thisBritish Standard is licensed to

Giorgio Cavalierion February 08, 2001

This is an uncontrolled copy.Ensure use of the most current

version of this standard bysearching British Standards Online

at bsonline.techindex.co.uk

BRITISH STANDARD BS 5589:1989

Code of practice for

Preservation of timber

UDC 674.048:634:674

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BS 5589:1989

This British Standard, having been prepared under the direction of the Timber Standards Policy Committee, was published under the authority of the Board of BSI and comes into effect on 29 September 1989

BSI 04-1999

First published September 1978First revision September 1989

The following BSI references relate to the work on this standard:Committee reference TIB/30Draft for comment 87/52668 DC

ISBN 0 580 17083 7

Committees responsible for this British Standard

The preparation of this British Standard was entrusted by the Timber Standards Policy Committee (TIB/-) to Technical Committee TIB/30 upon which the following bodies were represented:

British Railways BoardBritish Tar Industry AssociationBritish Wood Preserving AssociationBritish Woodworking FederationDepartment of the Environment (Property Services Agency)Department of the Environment (Building Research Establishment)Fibre Building Board Organization (FIDOR)Forestry CommissionTimber Growers9 United KingdomTimber Research and Development AssociationTimber Trade Federation

Amendments issued since publication

Amd. No. Date of issue Comments

Licensed Copy: Giorgio Cavalieri, ALSTO

M, 8-Feb-01, Uncontrolled Copy. BSI

BS 5589:1989

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Contents

PageCommittees responsible Inside front coverForeword ivSection 1. General introduction1 Scope 12 Use of this code 13 Performance ratings 14 Design considerations 35 Means of protection 36 Preparation of timber before treatment and handling after

treatment 47 Properties of treated timber 88 Safety 99 Checking preservative treatment 9Section 2. External woodwork above the damp-proof course in buildings10 General 1111 Hazards 1112 Performance 1113 Timber species 1114 Timber condition 1115 Preservatives 1216 Limitations of preservatives 1217 Methods of application 1218 Cutting after preservation 1219 Painting preservative treated timber 12Section 3. Agricultural and horticultural timbers20 General 1421 Hazards 1422 Performance 1423 Timber species 1424 Timber condition 1425 Preservatives 1426 Limitations of preservatives 1427 Methods of application 15Section 4. Timber for use permanently or intermittently in contact with sea or fresh water28 General 1829 Hazards 1830 Performance 1831 Timber species 1832 Timber condition 1833 Preservatives 1934 Methods of application 19Section 5. Timber for use as packing in cooling towers35 General 2036 Hazards 2037 Performance 2038 Timber species, quality and condition 20

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Page39 Preservatives 2040 Methods of application 2041 Waste disposal 20Section 6. Fencing timber42 General 2243 Hazards 2244 Performance 2245 Timber species 2246 Timber condition 2247 Preservatives 2348 Limitations of preservatives 2349 Methods of application 23Section 7. Timber for use in prefabricated buildings for temporary use in termite infested areas50 General 2651 Hazards 2652 Performance 2653 Timber species 2654 Timber condition 2755 Preservatives 2756 Limitations of preservatives 2757 Methods of application 27Section 8. Timber in timber frame housing58 General 2959 Hazards 2960 Performance 2961 Timber species 2962 Timber condition 2963 Preservatives 2964 Methods of application 30Table 1 Schedule of preservative processes applicable tothis British Standard 2Table 2 Hazard categories 4Table 3 Natural durability and treatability characteristicsof selected timbers 5Table 4 Expected minimum sapwood retention of CCAtreated timber 10Table 5 Preservative treatments for external woodwork inbuildings above the damp-proof course (hazard category 3) 13Table 6 Timber for agricultural and horticultural purposes with heartwood sufficiently durable to be used without treatment 14Table 7 Preservative treatments for timber in contact with the ground, soil or manure; also those likely to become permanently wet (hazard category 4) 16Table 8 Preservative treatments for timber subject to intermittentwetting or damp conditions (hazard category 3) 17Table 9 Suitability of timber for use in water 19Table 10 Preservative treatment for timber for use in contact with water 19



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PageTable 11 Preservative treatments for European redwood timber for use in packing in cooling towers (hazard category 4) 21Table 12 Timber with heartwood sufficiently durable to be used forfencing without treatment 22Table 13 Determination of moisture content of timber to be treated for use in fencing 23Table 14 Preservative treatments for fencing timber inperformance category A (desired service life of 40 years) 23Table 15 Preservative treatments for fencing timber in performance category B (desired service life of 20 years) 25Table 16 Preservative treatments for timber for use in buildings in termite infested areas (hazard category 4 because of termite risk) 28Table 17 Preservative treatments for timber for use in timber frame housing 30Publications referred to Inside back cover

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BS 5589:1989

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Foreword

This British Standard has been prepared under the direction of the Timber Standards Policy Committee. BS 5589 was first published in 1978 and amended in 1982 to include a new section on timber for use in buildings in termite infested areas. This revision has been prepared to bring the standard up to date. It includes a new section on timber for use in timber frame housing. This revision of BS 5589 supersedes BS 5589:1978 which is withdrawn.In this edition a general introductory section is followed by seven sections, each of which deals with an area of use for timber. As the need arises, consideration will be given to the inclusion of further sections dealing with other specific end-uses. For many of these uses there exist or are planned product specifications in which detailed attention is given to structural and manufacturing considerations but in which often only brief consideration can be given to requirements for durability or preservation. In most cases, this British Standard considers these latter requirements in more detail and has tried to obtain more uniformity between them. It is hoped that as new or revised product specifications are prepared, they will make full reference to the appropriate sections of this British Standard.In this revision, the concept of desired service life for a component has been retained to enable a specifier or user to make a choice of performance requirement. Alternative treatments can then be selected to achieve the desired life on the basis of cost and availability. The figures used to categorize desired service life relate solely to protection against biodegradation and have to be considered together with the aspects of design, maintenance and service environment which all contribute to the actual service life of a component. Clause 3 of this British Standard explains the basis on which service lives were selected. This basis sometimes differs from that used, either implicitly or explicitly, in certain other British Standards, e.g. for farm buildings where considerations such as building financing may be involved. Clause 3 also includes reference to the proposed European method of classifying decay risk. This classification is introduced in readiness for the intended harmonization of approvals for wood preservatives and preserved wood with the European Economic Community (EEC).Technical Committee 38 Durability of wood and wood-based products of the European Committee for Standardization (CEN) has just commenced work, under a mandate from the Commission of the European Economic Community (EEC), on the classification of biological hazards and durability of timber, performance of treated timber, and the performance testing of preservatives. With the publication of European Standards arising from this work, this British Standard will be amended, revised or withdrawn so as to remove any conflicting aspects.BS 5268-5 deals primarily with the requirements for preservative treatment of timber used structurally in buildings.Users of the product specifications referred to in this British Standard are advised to consider the desirability of third party certification of product conformity with those product specifications based on testing and continuing surveillance, which may be coupled with assessment of a supplier9s quality systems against the appropriate Part of BS 5750. Enquiries as to the availability of third party certification schemes in these cases will be forwarded by BSI to the Association of Certification Bodies. If a third party certification scheme does not already exist, users should consider approaching an appropriate body from the list of Association members.Users of this British Standard are advised to consider the desirability of assessment and registration of a supplier9s quality systems against the appropriate Part of BS 5750 by a third party certification body.



BS 5589:1989

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Reference was made in the first edition to a series of specifications published by the British Wood Preserving Association (BWPA). The majority of these have now been published as British Standards, but a British Standard relating to the use of boron as a wood preservative remains to be prepared. Reference has therefore again been made to a BWPA publication following its consideration by the responsible committee.A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application.

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pages This document comprises a front cover, an inside front cover, pages i to vi,pages 1 to 30, an inside back cover and a back cover.This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

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BS 5589:1989

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Section 1. General introduction

1 ScopeThis British Standard gives recommendations for the preservative pretreatment of timber to provide protection against biodegradation in certain specified end-use situations in the UK1). It recommends preservatives, processes and treatment levels suited to the hazards encountered in use and takes into account the natural durability and treatability of the timber employed. It does not deal with treatments regarded as remedial in nature, with those applied in situ, nor with those primarily designed to influence the performance of timber in fire.The preservative treatment of structural timbers, particularly those in buildings, is described in BS 5268-5.NOTE The titles of the publications referred to in this standard are listed on the inside back cover.

2 Use of this codeThis standard is part of a group of British Standards dealing with the preservative pretreatment of timber. BS 1282 forms an introduction to the subject; it gives general information on the biological hazards to which timber may be exposed, types of preservative and their properties and the methods of treatment by which they can be applied.This code has been written primarily for specifiers and users of treated timber, and is concerned with those aspects of the preservative treatment that affect the end-use of the treated product. Section 1 covers matters common to all the uses dealt with in the other sections. In these other sections specific recommendations are given for the treatment for individual end-uses. In most cases a choice of treatment is offered and the level at which each should be applied is recommended.To specify a treatment using this British Standard it is essential to cite both the relevant section for the proposed end-use and the desired service life. In addition, the required preservative and process should be specified in accordance with the relevant section of this standard. In the choice of the preservative it is necessary to take into account factors such as the timber species to be treated, the need for subsequent painting or glueing, etc.

Those aspects of preservative treatment which are principally the concern of the preservative manufacturer and treater are dealt with by a group of British Standard preservative and processing specifications. These cover the chemical compositions of the preservatives and give details of the processes involved in their application. In most cases, however, they leave the specifier to choose the intensity of the treatment applied2).Table 1 gives a list of processes and relevant British Standard specifications.

3 Performance ratings3.1 General

The organisms that can attack wood and conditions under which the wood becomes degraded are discussed in BS 1282.If timber becomes wet and remains wet, e.g. moisture content exceeds 20 %, then eventually it is likely to decay. The rate at which this decay occurs is related to the inherent durability of the timber, i.e. the degree to which it possesses a natural resistance to decay. The durability of heartwood varies with species; the heartwood of some species possesses a resistance to decay which renders the process extremely slow, while the heartwood of others, and the sapwood of all species, possess little resistance. Timbers in this latter group, with little natural durability, require preservative protection when used under wet conditions.The incidence of insect attack in the UK is sporadic since it depends on the introduction of the adult insects. Where attack may cause serious damage, as in the case of Hylotrupes bajulus, then preservative treatment is essential3).

3.2 Service environments

The proposed end-use of the timber may be such that:

a) the timber is constantly exposed to adverse conditions;b) the exposure to adverse conditions is intermittent;c) the exposure to adverse conditions is accidental.

1) Section seven deals with the preservation of timber for use overseas in termite infested areas.2) In the past it was the usual practice to combine into a single British Standard the requirements for the composition of a type of preservative together with information on processing and the recommended level of treatment for specific uses. For an interim period recommended levels of treatment will be found both in these older standards and in the newer standards for particular commodities.3) See The Building Regulations 1985.

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Table 1 Schedule of preservative processes applicable to this British Standard

Timber in the ground, e.g. fence posts or poles, and timber in water quickly acquire and retain a high moisture content, and are thus constantly at risk. Additionally, timber used in sea or brackish water is liable to attack by marine organisms; timbers which have a natural resistance to fungal decay are not necessarily also resistant to marine borers. Timbers used in environments of this kind are constantly exposed to adverse conditions and there is a high risk of early failure of susceptible species unless preventive measures are taken.When outdoor timbers are not in ground contact, exposure to the weather will cause the moisture content of the wood to fluctuate and there will be periods when fungal decay could develop. Protective coatings such as paints rarely provide complete and permanent protection from water ingress; thus preservative treatment of all susceptible external timbers is advisable.The exposure of internal timbers to wet conditions may occur because of design faults, condensation, failure of other materials, poor workmanship or lack of maintenance.

In many such instances, should decay occur, the resultant damage may be easy to remedy; but where experience has shown that there is a high risk of decay, or where the resultant damage would be difficult or expensive to repair, or where the associated weakening would endanger life or the integrity of the structure, then preservative treatment is recommended.The level of preservative treatment recommended depends not only on the risk of attack but also on the expected life of the commodity. In some cases it has been possible to lay down conditions suited to two levels of performance, e.g. fencing timber with desired lives of 20 or 40 years. The performance requirements in the individual commodity specifications are based on timbers and levels of preservation readily available commercially. In special cases where longer lives are required, a higher standard of treatment may be achieved by more severe processing of a restricted number of timber species.

Preservative and process Essential parameters for specification according to end-use

Creosote (tar oil) pressure process

Creosote complying with BS 144-1a applied in accordance with BS 144-2b and the treatment cycle details given in this British Standard for the required end-use

Creosote immersion process

Creosote complying with BS 144-1a applied by complete submersion giving the immersion period required

Creosote hot-and-cold open tank process

Creosote complying with BS 144-1a applied in accordance with BS 144-2b with or without reheating

Copper/chromium/arsenic (CCA) full-cell process

CCA complying with BS 4072-1 applied in accordance with BS 4072-2 and the treatment cycle details given in this British Standard for the required end-use

Organic solvent (OS) double vacuum process

OS preservative complying with BS 5707-1 and applied in accordance with BS 5707-3 and the treatment cycle details given in this British Standard for the required end-use

Organic solvent (OS) immersion process

OS preservative complying with BS 5707-1 applied in accordance with BS 5707-3 and the treatment cycle details given in this British Standard for the required end-use

Pentachlorophenol (PCP) in heavy oilc double vacuum process

PCP in heavy oilc complying with BS 5707-2 applied in accordance with BS 5707-3 and the treatment cycle details given in this British Standard for the required end-use

Boron diffusion process Timber treated with disodium octaborate in accordance with the methods specified in BWPA Manual 1986

a In preparation. Pending publication, reference should be made to BS 144 and BS 3051.b In preparation. Pending publication, reference should be made to BS 913.c The reference to heavy oil applies to the boiling range of the solvent given in BS 5707-2.



BS 5589:1989

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Where risk of attack is intermittent or sporadic in character, the concept of performance for the treated timber has less meaning, since the hazard may or may not present itself and its severity is unlikely to be known in advance. Treatments for commodities in this category are rated, therefore, in terms of period of effectiveness, i.e. the time during which the preservative can be expected to remain in sufficient quantity to provide effective protection.It is essential to realize that the life cited in a performance clause (clauses 12, 22, 30, 37, 44, 52 and 60) of this British Standard is not a guarantee of performance but merely indicates the service life against which the specifications for timber treatment were drawn up, assuming good design and normal conditions of use. It relates solely to the resistance of the timber to biodegradation and it has to be borne in mind that other factors, such as mechanical damage or failure of other elements of the construction, may limit the life of the complete commodity. The lives predicted have in some cases not been established by direct service evidence and therefore may be subject to revision as more experience is gained.

3.3 European hazard categories

It is clear from the considerations in 3.2 that timber in service may be attacked by wood-destroying organisms if certain conditions arise or prevail and that the probability that this might happen can be predicted from an understanding of the environmental conditions that are likely to exist for the various service situations in which timber is used. In other words, different service situations can be associated with a level of risk that fungal decay or insect attack will occur. Thus in a persistently wet environment the chance of fungal attack occurring is higher than in a relatively dry situation. Where the timber will be constantly damp, treatment with an appropriate preservative or the use of a naturally durable timber may be considered essential; where the timber will always be dry, treatment with a preservative or the property of natural durability may be unnecessary. This philosophy has been developed by the European Homologation Committee into a simple rating system employing hazard categories (see Table 2). Thus each timber component in use can be related to a particular hazard category, allowing a common understanding of the preservation requirements for that component within the EEC. Hazard categories are assigned to each section in this British Standard in preparation for the intended harmonization of preservation requirements throughout the EEC.

4 Design considerationsThis British Standard is not a design code for timber components or structures. However, detailed design of a structure which includes timber can have such an important influence on the timber9s durability that it is essential that the design be considered in conjunction with the possible need for preservative treatment.In some cases, the risk of timber degradation by biological agents can be minimized by design of the structure concerned. Where a design cannot practically provide acceptable immunity, it will have to be modified and reinforced by the use of naturally durable timbers or timbers treated with preservative. In other situations, such as timber in contact with the ground, or in dock and harbour work, design can do little to reduce the hazard; in these circumstances the use of naturally durable timbers or appropriate preservative treatment is essential if adequate service life is to be achieved.Where possible, reference is made to other standards dealing with features and details of construction which constitute good practice. Examples of design features to consider are provision of adequate moisture barriers, throating of ledges and cills, adequate ventilation of cavities, provision of damp-proof courses and vapour barriers, attention to the sealing of end-grain and joints and avoidance of water traps.It should not be assumed that the use of a naturally durable or preservative treated timber obviates the need for good design and workmanship. The preservative treatments recommended for the various commodities in subsequent sections are complementary to good design and workmanship, not a substitute for it.

5 Means of protectionThe recommendations in most of the individual sections of this code provide an option of choosing a timber4) with sufficient natural durability (or resistance to insect attack) or a less durable timber which requires preservative protection. If reliance is placed on natural durability alone it should be realized that this is a property of only the heartwood of the timber concerned. The sapwood of all timber is susceptible to decay and, with certain exceptions (notably spruce and other timbers in which heartwood is not distinct), it is only the sapwood that is attacked by wood-boring insects. On the other hand, marine borers can also attack heartwood. For many softwoods and certain hardwoods, the exclusion of sapwood is not a practical proposition.

4) Timbers have been named throughout according to their standard names listed in BS 589 and BS 881.

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BS 5589:1989

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Table 2 Hazard categories

If an amount of sapwood is present, the loss of which would render the commodity unfit for its intended use, or where the sapwood is indistinguishable from the heartwood, consideration should be given to the need for preservative treatment. Such consideration should take into account the proposed end-use but disregard the durability rating of the heartwood.The preservative treatments recommended are restricted to those for which there is a suitable British Standard or BWPA (see Table 1) specification and which are available commercially in the UK. All wood preservatives used in the UK have to be approved under the Control of Pesticides Regulations, 19865). The recommendations in this British Standard take into account both the natural durability, in the UK, of the timbers concerned and their treatability as defined in BRE Digest 296. Table 3 is derived from BRE Digest 296 and gives information on the most commonly used timbers. It also gives guidance where available on the treatability of the sapwood of these timbers.

6 Preparation of timber before treatment and handling after treatment6.1 Before treatment

6.1.1 General. It is essential that timber submitted for preservative treatment is in a suitable condition as in 6.1.2 to 6.1.5.6.1.2 Condition of timber. The timber should be free from all signs of attack by wood-destroying fungi or insects.NOTE Timber showing signs of attack by sap-stain fungi or pinhole borers is acceptable, subject to agreement between the interested parties.

As preservative treatment of seasoned timber does not afford protection against deep-seated infection or dote, care should be taken to exclude timber infected with incipient decay.The surfaces of the timber should be free from extraneous matter, e.g. water, mud, dirt and inner and outer bark. They should also be free from any paint, polish, or other surface finish.If timber is frozen penetration is limited. Care should be taken not to treat timber in this condition.6.1.3 Moisture content. It is essential that the moisture content of the timber is at the correct level6) for the type of treatment to be received.For boron diffusion it is essential that the moisture content be greater than 50 %.Undried timber or timber with a moisture content higher than 28 % may be prepared by the Boulton Process for treatment with creosote as specified in BS 144-27), though extreme caution should be exercised when using this procedure.All other treatments require the moisture content to be below 28 % throughout the zone to be treated. For creosote and CCA treatment it is essential to dry to this moisture content before treatment, and for certain end-use situations a lower moisture content may be required.Since organic solvent preservatives do not affect the moisture content of treated wood, commodities should be treated with these preservatives in their final machined state and at the moisture content consistent with their end-use.Methods for determining moisture content are detailed in, for example, BS 4072-26).

Hazard category

Risk of fungal decay Examples

1 Where conditions of use involve negligible risk Joinery inside dwellings, e.g. stairs and architraves

2 Where there is low risk Timber in normal pitched roofs; joists in ground floors

3 Where experience has shown there is a high risk Cladding and external joinery

4 Where there is a continually hazardous environment and unacceptable risk

Fence posts; sleepers; freshwater lockgates

M As for category 4, but in the marine environment Marine piling, piers and jetties

5) The Health and Safety Executive is the approving body.6) For poles the moisture content requirements and method of determination are given in BS 1990-1.7) In preparation. Pending publication, reference should be made to BS 913.



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Table 3 Natural durability and treatability characteristics of selected timbersCommon namea or commercial designationb Natural durability

(heartwood only)c Treatabilityd

Heartwood Sapwood

Abura P MR P

Afrormosia VD ER n/a

Afzelia VD ER n/a

Agba P R P

Alder P P n/a

Ash European P MR MR

Balau (not including red balau) D/VDe n/a n/a

Basralocus VD ER n/a

Beech European P P P

silver ND ER P

Birch European P P P

paper ND MR MR

yellow P MR P

Cedar western red (imported) D R R

western red (British grown) MD R R

Chestnut European horse P P P

sweet D ER n/a

Douglas fir larch (USA and Canada) MD R/ER n/a

Ekki VD ER MR

Elm Dutch ND MR P

English ND MR n/a

rock ND R n/a

white ND MR P

wych ND R n/a

Fir balsam ND R n/a

Douglas (British grown) MD R MR

Douglas (north American coastal) MD R n/a

Douglas (north American mountain) MD ER n/a

grand ND R P

noble ND MR n/a

silver ND MR P

Greenheart VD ER n/a

Guarea VD ER P

Hem-fir (USA and Canada) ND R n/a

Attention is drawn to the footnotes at the end of the table.

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Table 3 Natural durability and treatability characteristics of selected timbersCommon namea or commercial designationb Natural durability

(heartwood only)c Treatabilityd

Heartwood Sapwood

Hemlock western ND R n/a

Idigbo D ER MR

Iroko VD ER n/a

Jarrah VD ER n/a

Kapur Malaysian VD ER n/a

Sabah VD ER n/a

Karri D ER n/a

Kempas D R n/a

Keruing Malaysian MD R MR

Sabah MD MR MR

Larch Dunkeld (UK) MD R MR

European MD R MR

Japanese MD R MR

Tamarack MD R n/a

Western MD R n/a

Lauan f f f

Lime P P P

Louro red D ERe MR

Mahogany African MD ER MR

American D ER n/a

Makor VD ER MR

Merbau D n/a n/a

Meranti f f f

Oak American red ND P n/a

American white D ER MR

European D ER P

Japanese De n/a n/a

Tasmanian MD R P

Turkey MD ER P

Obeche ND R P

Okan VD ER R

Opepe VD MR n/a

Padauk Andaman VD MR n/a

Burma VD ER n/a

Attention is drawn to the footnotes at the end of the table.



BS 5589:1989

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Table 3 Natural durability and treatability characteristics of selected timbers

Common namea or commercial

designationb Natural durability

(heartwood only)cTreatabilityd

Heartwood Sapwood

Pine American pitch MD R P Canadian red ND MR P Caribbean pitch D MR P Corsican ND MR P Jack ND MR P lodgepole ND R n/a maritime MD R P Parana ND MR P Ponderosa ND MR P Radiata ND P P Scots ND MR P Western white ND MR P yellow ND MR P Southern yellow group ND MR P

Ramin P P PRedwood European ND MR PSapele MD R MRSeraya f f f

Southern pine (USA) ND MR PSpruce Eastern Canadian ND R n/a

Engelmann ND R n/a European (Whitewood) ND R n/a pine-fir (SPF) (Canadian) ND R n/a Sitka ND R MR

Sycamore P P PTeak VD ER n/aUtile D ER n/aWalnut African MD R n/aWestern whitewoods (USA) ND R n/aWhitewood European ND R n/aa The common names used in this table are defined in BS 589 and BS 881.b Where a timber consignment is purchased under a commercial designation, e.g. hem-fir or spruce-pine-fir (SPF), the commercial designation should be referred to in this list, not the individual species within the consignment.c Durability grades are: VD

D

MD

ND

P

very durabledurable

moderately durable

non-durable

perishableThe durability of the sapwood of all species is either perishable or non-durable.d Treatability groups are: ER

R

MR

P

n/a

extremely resistantresistant

moderately resistant

permeable

data not availableFurther details on durability and treatability may be found in BRE Digest 296.e Provisional rating. Balau can include some species assessed as MD.f The hardwoods known severally as meranti, seraya or lauan (shorea, parashorea and pentacme species) are sold commercially in mixed groups according to colour. The individual species within each group can have different durability and treatability properties and it is therefore difficult to assign a single rating to a mixed species consignment. In general, the species concerned vary from non-durable to durable and fall into the treatability groups R and ER. However, where the timbers are used for external joinery (section 2 of this British Standard) they should be regarded as in need of treatment and belonging to treatability group MR (see clause 13).

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6.1.4 Fabrication before treatment. All cutting, drilling, profiling and sanding of the timber should be carried out before treatment. All wood waste arising from these operations should be removed before treatment.Sawn timbers rated as resistant to preservative, 75 mm or thicker and intended for exterior use, may benefit from incising before treatment.6.1.5 Mixed charges. Timbers for which different schedules are appropriate, due to either size or species, should not be treated in the same charge, unless the most intense schedule can be applied without detriment to the more easily treatable timbers. If charges of mixed species or timber of different resistance to penetration are to be treated, the treatment schedule should be that appropriate to the most resistant of the timber species present and the largest section size.

6.2 After treatment

6.2.1 General. It is essential that timbers which are cross-cut, notched or drilled for bolts after any impregnation treatment have the exposed surfaces or bolt holes liberally treated by brushing, spraying or dipping with a wood preservative as recommended by the manufacturer unless otherwise specified in the relevant commodity specification. It should be understood that this does not restore the full value of the original treatment.If rip-sawing or profiling is carried out after treatment, it is essential to retreat the timber in accordance with the original specification.6.2.2 Copper/chromium/arsenic (CCA). Timber treated with CCA preservatives becomes wet during processing and a period of redrying may be required after treatment. Even where the nature of the commodity does not require such redrying, a period of 7 days before use should be allowed for the preservative salts to fix, i.e. become non-leachable. It is essential to stack timber carefully during this period because wetting and drying will cause timber movement and in some cases may cause distortion. It is essential that metal fittings are of a suitable composition and that they are not applied to the treated wood until this fixing period has elapsed (see BS 4072-2).

6.2.3 Creosote and organic solvent (OS) preservatives. The moisture content of timber is not increased by treatment with creosote or organic solvent preservatives and in this respect the product can be used immediately after treatment. However for organic solvent preservatives in certain situations, e.g. prior to painting or for enclosed use, time should be allowed for the carrier solvent to evaporate before further processing or installation. Evaporation can be facilitated by open stacking, preferably under cover in a well ventilated area, and will normally take 2 to 7 days according to uptake of preservative and prevailing conditions.6.2.4 Boron diffusion. Boron diffusion treatment is carried out on green timber at source and treated timber is usually supplied already dried. For most purposes timber treated in this way can be machined or worked on site without retreatment of cut surfaces, with the exception of longitudinal conversion of timber more than 50 mm thick, which is not recommended. It is essential to protect boron-treated timber against wet weather conditions during prolonged storage.

7 Properties of treated timber7.1 General

The main types of preservative employed (creosote, water-borne and organic solvent) have widely different secondary properties which influence the field in which each has a particular value. Where these properties impose a limitation on their use for a particular commodity this is noted in the appropriate section of this standard. Some general comments on the utilization of treated wood are given in this clause.

7.2 Strength

Normal preservative treatment does not affect the strength properties of timber to any extent that is of practical significance.

7.3 Metal components

Under some conditions, metal fastenings may become corroded through contact with CCA treated timber and the preservative manufacturer should be consulted about any possible interactions of this kind (see BS 4072-2 for fuller information).Provided the timber remains dry there is little risk of interaction of treated wood with ferrous metal fittings. Where corrosion of steel or galvanized steel may be expected to occur, even with untreated timbers, corrosion is more severe in the presence of CCA preservatives. It is important not to apply any metal fittings until the period of fixation of these preservatives is complete.



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There is very little service evidence on which to base advice on the interaction of preservative treated wood with other metals.Precautions should be taken to avoid contact between uncoated aluminium sheeting and copper-containing preservatives.

7.4 Adhesives, sealants and weatherseals

The interaction of adhesives, sealants and weatherseals with preservatives is a complex subject and cannot be adequately covered in general terms. Use of these materials with preservative treated timber should not be undertaken without first having sought advice from the manufacturer.

7.5 Decorative finishes

In general, timber treated with a water-borne or organic solvent preservative, which is formulated for subsequent painting, can be painted or stained normally. However, it is important that an adequate drying period should be left between preservative treatment and finishing. This can vary for different preservative types and the manufacturer9s advice should be followed.However, highly porous zones are sometimes encountered, particularly in European redwood, which can rapidly absorb excessive amounts of preservative solution.Such timber can give rise to finishing problems, particularly if treated with organic solvent preservatives, and extended drying periods will be necessary.Copper naphthenate preservatives may give rise to staining problems with light coloured paints. Timber treated with creosote or PCP in heavy oil is not recommended for overpainting.

7.6 Flammability

The solvents commonly used for applying organic solvent preservatives are flammable and it is essential that care be exercised in applying such materials. However, once the solvent has evaporated from treated wood the timber is no more flammable than untreated wood.When the surface of creosoted timber has dried, the timber is no easier to ignite than untreated timber, but it has different burning characteristics from those of untreated timber.

8 Safety8.1 Solutions

All preservatives should be handled with care and in accordance with The Control of Pesticides Regulations 1986 and manufacturers9 specific instructions.

8.2 Treated timber

When handling freshly treated timber, protective gloves should be worn. For timber treated with creosote or organic solvent preservatives adequate ventilation is also required. CCA-treated timber should be held for 48 h or till drip dry, whichever is the longer, before dispatch or erection.No special precautions are necessary in handling timber treated with water-borne salts or organic solvent preservatives once the timber has dried, but it is essential to observe the normal practice of washing hands before handling food or smoking. Timber treated with creosote or PCP in heavy oil does not dry out in the same way as that treated with water-borne or organic solvent preservatives, and continued precautions may be necessary if the surface is oily.If it is necessary to machine or sand treated timber, an efficient dust extraction system should be used.

8.3 Waste disposal

There are mandatory requirements governing the safe disposal of wood-preservative and treated-wood wastes, e.g. The Control of Pollution Act 1974. For information concerning the recommended methods for the disposal of these materials reference should be made to DOE Waste Management Paper No. 16: Wood Preserving Wastes.It is essential that wood waste from treated timber is not used for animal litter.

9 Checking preservative treatment9.1 General

There are two aspects of preservative treatment which the user commonly wishes to check. The first is whether the treatment has been carried out at all and the second is whether it has been carried out according to the specified procedure. The former is more easily verified than the latter.

9.2 Detection of preservative

The chemicals used in wood preservation comprise a diverse range of substances differing in the ease with which they can be detected in wood in situ.Creosote is recognizable by its odour and colour; copper-containing preservatives such as CCA and copper naphthenate colour the wood green.Other preservatives are usually colourless. Some products may be detected by spray reagents but others may need chemical analysis (see BS 5666-2).

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9.3 Quantitative requirements

9.3.1 General. For most preservatives there is a chemical procedure whereby it is possible to estimate the amount of preservative in a sample of treated wood (see BS 5666). Although this information does not allow a direct conclusion as to whether or not the specified treatment has been carried out it can often provide an indication of the type of treatment given.9.3.2 Boron diffusion and creosote treatments. Timber treated by the boron diffusion process is required by its specification to have a defined cross-sectional loading and a defined core loading on the basis of an 80 % compliance (see BWPA Manual 1986). Creosote treatments are specified in terms of a minimum average net retention and an extended pressure period.9.3.3 Other treatments. For preservative processes other than boron diffusion and creosote, specifications are defined in terms of processing parameters and thus there are no defined loading requirements. Verification of treatment thus rests on knowledge of the process carried out.Many treatment plants are largely automatic in their operation (though with the possibility of operator intervention) and many preservation processors issue treating certificates to assure customers that the requirements of any specification named on a certificate have been satisfied. However the only certain way to be sure that treatment has been carried out as required is to witness all aspects of the treatment process.NOTE With organic solvent preservatives, most preservative manufacturers will express an opinion concerning the loading of preservative in timber which is likely to result from a given treatment schedule. However, there is insufficient agreement to permit information on this aspect to be included in this British Standard. When appropriate data have been generated and collected, it is expected that these will be published as an amendment to this code.

In the case of CCA preservatives, analysis of species with permeable and moderately resistant sapwood [excluding those species where the sapwood and heartwood cannot be differentiated, e.g. whitewood (see Table 3)] can provide a good indication of whether the recommendations of this British Standard have been complied with. With these species the sapwood should be fully penetrated and have a minimum sapwood retention as shown in Table 4.

Table 4 Expected minimum sapwood retention of CCA treated timber

Any sample providing a result significantly below the values given in Table 4 is unlikely to have been treated as recommended by this British Standard. For those few timber species with more resistant sapwood the retentions quoted in Table 4 apply to that portion of the sapwood which is fully penetrated by the preservative.

Treatment solution concentration

Minimum sapwood retention

g/L kg/m3

20 8

30 12

40 16

50 20

60 24



BS 5589:1989

BSI 04-1999 11

Section 2. External woodwork above the damp-proof course in buildingsNOTE It is essential to read this section in conjunction with section 1.

10 GeneralThis section gives recommendations for the species and preservative treatment of any external woodwork in a building that is situated above the damp-proof course of the building. It does not cover the quality requirements for such woodwork, for which guidance should be sought in BS 1186-1 for joinery woodwork and BS 5268-2 for structural timbers. Examples of items covered by this section are as follows:

11 HazardsExternal woodwork above the damp-proof course in buildings is exposed to intermittent wetting, and if timbers of low natural durability or those containing sapwood are used decay may occur.Attack by wood-boring beetles is very rare on painted external woodwork. Occasionally it may be found in unpainted external components where sapwood is present.

12 PerformanceTwo performance categories are defined:

performance category A: desired service life of 60 years;performance category B: desired service life of 30 years.

13 Timber speciesThe heartwood of those timbers rated as durable (see Table 3) or better (D or VD) may be used untreated for performance category A, and those rated as moderately durable or better (MD, V or VD) may be used untreated for performance category B. All other timbers require treatment; any timbers which contain quantities of sapwood, the loss of which would render the commodity unfit for its intended use or where the sapwood is indistinguishable from the heartwood, require treatment.Those hardwoods known severally as meranti, seraya, or lauan (shorea, parashorea and pentacme species) vary in their natural durability and cannot be assigned satisfactorily to any one durability class when described by current commercial nomenclature. For the present and for the purposes of this British Standard they should be regarded as requiring treatment.Mixed charges of timber for which different schedules are appropriate, due to either size or species, should not be treated in the same charge, unless the most intense schedule can be applied without detriment to the more easily treatable timbers. The treatment schedule for charges of mixed species of timber of different resistance to penetration should be that appropriate to the most resistant of the timber species and the largest section size, present in the given charge.

14 Timber conditionThe timber before treatment should be in a suitable condition as recommended in 6.1.Good preservation of these commodities requires maximum end-grain penetration. This is usually greatest when timbers are treated before assembly, although other considerations, such as any need to machine after assembly, may make it preferable to treat at a later stage.For fabricated components, those materials which are used to hold the individual members together should be of equivalent durability to the treated timber. Thus wooden dowels should be of an appropriate durability rating or treated as defined under clause 13; adhesive should be of an exterior grade and should not break down in service.Since organic solvent preservatives do not affect the moisture content of treated wood, commodities should be treated with these preservatives in their final machined state and at the moisture content consistent with their end-use, e.g. for external joinery 16 3 % (m/m) and for internal joinery between 10 2 % (m/m) and 15 2 % (m/m) according to the type of heating installed in the building (see BS 1186).

window frames

casements and sashes

surrounds for non-wooden windows

doors (excluding flush doorsa)

door-frames

porches

cladding

soffits

fascias

barge boards

framing

purlins only where all or part of the member

rafters is exposed to the weather

joistsa Flush doors are not included because of the difficulties in establishing suitable treatments.

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15 PreservativesThe following preservatives may be used. Their suitability for specific uses is given in Table 5.

a) CCA water-borne preservatives complying with BS 4072-1.b) Coal tar creosote complying with BS 144-18).c) Organic solvent preservatives complying with class F or class F/N of BS 5707-1. NOTE With this class of preservative the inclusion of a water repellent in the formulation is advantageous, but not essential.

d) Disodium octaborate complying with the BWPA Manual 1986.

16 Limitations of preservativesReference should be made to section 1, particularly with respect to the compatibility of the preservative with paints, finishes, adhesives, and sealants.Water-borne treatment with CCA preservatives will cause swelling of the wood. The original dimensions will normally be recovered on redrying, but the timber should be carefully stacked during this process to avoid distortion. If grain-raising is unacceptable, planed timber should not be treated with water-borne preservatives.

17 Methods of application17.1 General

The treatments to be used depend upon the performance category required and the treatability of the timber species used. These are given in Table 5.

17.2 Vacuum/pressure processes

CCA preservative solutions should be applied by a full-cell process in accordance with BS 4072-2.Creosote should be applied in accordance with BS 144-29). Use of an empty-cell process is normally to be preferred, except for resistant timbers. The end requirement of processes using creosote is specified in terms of a minimum average net retention and an extended pressure period.

17.3 Double vacuum process

The application of organic solvent preservatives by the double vacuum process should comply with BS 5707-3.

17.4 Immersion

Organic solvent preservatives and creosote complying with BS 144-18) may be applied by immersion. It is essential that the timber is completely submerged in the preservative for the period specified in Table 5.

17.5 Boron diffusion

This process has to be carried out on timber that has not dried since felling and should comply with the BWPA Manual 1986. Seasoned timber cannot be treated by this process.

18 Cutting after preservationAs far as possible all sawing, planing, cross-cutting, drilling or other woodworking should be carried out before treatment. If this is not practicable, any surface exposed by drilling, cross-cutting, etc., subsequent to treatment should be given two liberal brush or spray applications of the preservative solution as recommended by the appropriate manufacturer. This is particularly important where horns are cut off on site. These recommendations do not apply to boron diffusion treated timber.

19 Painting preservative treated timberTimber freshly treated with creosote cannot be overpainted. With other preservatives it is important that the solvent be allowed to evaporate from the treated timber and that the timber be allowed to dry to the moisture content recommended by the manufacturer before overpainting. This particularly applies to water-borne preservatives of the CCA and disodium octaborate types.For timber treated with organic solvent preservatives or with disodium octaborate, it is essential that the surfaces to be exposed to the weather are painted or given some other protective finish which will be maintained in service.Although most organic solvent preservatives complying with BS 5707-1 are suitable for overpainting, etc., paint compatibility is not a requirement of that standard. Users should satisfy themselves of the compatibility of the particular preservative with their paint or finish.

8) In preparation. Pending publication, reference should be made to BS 144 for treatment by the pressure process and BS 3051 for treatment by immersion.9) In preparation. Pending publication, reference should be made to BS 913.



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Table 5 Preservative treatments for external woodwork in buildings above the damp-proof coursea (hazard category 3)

Performance category

Timber treatability

ratingb

Copper/chromium/arsenic by full-cell processc

Creosote by pressure process

Organic solvent preservatives by double vacuum processd

Period of immersion for

organic solvent

preservativesd or creosote

Boron diffusiond

Vacuum period

Pressure period

Solution concentration

Minimum net

retention

Extended pressure

period

Initial vacuum Pressure stage Final vacuum stage

Vacuum Period Pressure Period Vacuum Period

min min g/L kg m3 min bar min bar min bar min min

ADesired service life of 60 years

P and MR (20 mm thick or less)

30 60 30 100 60 0.33 3 0 3 0.67 20 60e Not recommended

P and MR (thicker than 20 mm)

30 90 30 100 60 0.33 5 1 5 0.67 20 Not recommended

Not recommended

R and ER 60 180 30 100 120 Not recommended Not recommendedNot recommended

BDesired service life of 30 years

P and MR 30 60 20f 80 60 0.33 3 0 3 0.67 20 3e Recommended

R and ER 30 90 30 80 120 0.83 10 1 60 0.83 20 Not recommended

Recommended

0.83 10 2 15 0.83 20

NOTE 1 bar = 105 N/m2 = 105 Pa = 750 mm Hg. All pressures quoted are gauge pressures, i.e. relative to normal atmospheric pressure as zero.a For the purposes of this table, the following apply:

a) western hemlock, when used specifically for door construction, should be treated as a MR timber;b) the hardwoods known severally as meranti, seraya, or lauan (shorea, parashorea and pentacme species), when used for joinery purposes, should be treated as MR timbers;c) if the heartwood is of adequate natural durability (see clause 13) the relevant treatability rating should be taken as that of the sapwood (see Table 3).Mixed timber consignments should be rated equivalent to the least treatable timber species in the consignment.

b P = permeable, MR = moderately resistant, R = resistant, ER = extremely resistant.c In consignments identified by the supplier as consisting of 80 % or more sapwood (class P and MR), excessive uptake of preservative is likely. In these instances a Lowry empty cell process with the same pressure and final vacuum stages and solution concentration may be used.d These treatments are restricted to woodwork in which the surface or surfaces exposed to the weather will be painted or given some other protective finish which will be maintained in service.e Pinus species only.f Lowry empty-cell process in accordance with BS 4072-2 may be used as an alternative using a solution concentration of 30 g/L.

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Section 3. Agricultural and horticultural timbers

NOTE It is essential to read this section in conjunction with section 1.

20 GeneralThis section gives recommendations for the species and preservative treatment of timber intended for use in buildings for the housing of livestock, the growing of vegetables, fruit and flowers and the storage of equipment and produce. It does not cover fencing, which is dealt with in section 6. Examples of items covered by this section are as follows:

agricultural: timber in buildings and equipment for housing livestock or the storage of farm products and machinery;horticultural: timber in buildings and equipment for the growing, storage and processing of produce.

21 HazardsThe timbers most liable to decay are those which remain wet for long periods. They include timber in contact with the ground, soil or manure and timber in buildings with a high condensation risk, such as certain animal houses, glass houses, and buildings used for drying and storing crops.Timbers which are subject to intermittent wetting, although at lower risk, may also decay.Insects are not important as a cause of damage to external timbers, but the sapwood of internal timbers in farm buildings may be attacked.

Table 6 Timber for agricultural and horticultural purposes with heartwood sufficiently durable to be used without

treatment



23 Timber species23.1 Timber not requiring treatment

The heartwood of timber species with the durability ratings shown in Table 6 can be used in the situations shown without preservative treatment. All sapwood is non-durable; where the cross section contains some sapwood, the loss of which would render the commodity unfit for its intended use, treatment is required.

23.2 Timber requiring treatment

Timber species with a durability rating less than the appropriate rating shown in Table 6 for the desired performance category should be treated appropriately as described in clauses 24 to 27.

24 Timber conditionThe timber before treatment should be in a suitable condition as recommended in 6.1.Cutting of timber after treatment should not be permitted if the cut end is intended for use in the ground or in permanently damp conditions.

25 PreservativesThe following preservatives may be used. Their suitability for specific uses is given in Table 7 and Table 8.

a) CCA water-borne preservatives complying with BS 4072-1.b) Coal tar creosote complying with BS 144-110).c) PCP in heavy oil complying with BS 5707-2.d) Organic solvent preservatives complying with class F or class F/N of BS 5707-1.

26 Limitations of preservativesWood treated with any of the preservatives named in clause 25 is suitable for most horticultural or agricultural purposes, provided that any restrictions on use associated with approval of the preservative under The Control of Pesticides Regulations are observed. In addition the following precautions should be observed.

Performance category Situation

Timbers in contact with the ground, soil or manure; also those

likely to become permanently wet

(hazard category 4a)

Timbers subject to intermittent wetting (hazard

category 3a)

A Desired service life of 50 years

Very durable (VD)b Durable or better (D or VD)b

B Desired service life of 20 years

Durable or better (D or VD)b

Moderately durable or better (MD, D or VD)b

a See Table 2.b See Table 3.

10) In preparation. Pending publication, reference should be made to BS 144 for treatment by the pressure process and BS 3051 for treatment by immersion.



BS 5589:1989

BSI 04-1999 15

Seed boxes, internal timbers in greenhouses and any other timbers which will come into intimate contact with plants should not be treated with a preservative containing pentachlorophenol. With any organic solvent preservative and coal tar creosote, the solvent should be allowed to evaporate before the wood is put into service.Timbers freshly treated with CCA preservatives which are to come into contact with animals or foodstuffs should not be put into service until at least 7 days after treatment and subsequent thorough hosing with water. With any organic solvent preservative, the solvent should be allowed to evaporate before the wood is put into service. Foodstuffs should not be stored in contact with timber which has been treated with organic solvent preservatives or creosote, because of the risk of chemical migration or tainting. Some commodities, e.g. apples, are very susceptible to tainting and special advice should be sought regarding appropriate preservatives for their storage conditions.Creosoted timbers which will come into regular contact with animals should be treated by a process which minimizes the bleeding which may occur with preservative in service.


The treatments to be used depend upon the performance category required and the timber used. These are given in Table 7 and Table 8.


CCA preservative solutions should be applied by the full-cell process in accordance with BS 4072-2.Creosote should be applied under pressure in accordance with BS 144-211). Use of an empty-cell process is normally to be preferred, except for resistant timbers. The end requirement of processes using creosote is specified in terms of a minimum average net retention and an extended pressure period.

27.3 Hot-and-cold open tank process

When creosote is applied by the hot-and-cold open tank method the process should be in accordance with BS 144-212), but, where bleeding is to be minimized, there should be a final reheating stage of 80 C to 95 C before removing the timber from the tank.


The application of organic solvent preservatives and PCP in heavy oil by the double vacuum process should comply with BS 5707-3.

27.5 Immersion


11) In preparation. Pending publication reference should be made to BS 913.12) In preparation. Pending publication reference should be made to BS 144.13) In preparation. Pending publication reference should be made to BS 3051.

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Table 7 Preservative treatments for timber in contact with the ground, soil or manure; also those likely to become permanently wet (hazard category 4e)


Timber form and

treatability ratinga

Copper/chromium/arsenic by full-cell processb


Creosote by hot-and-cold

open tank process

PCP in heavy oil by double vacuum process

Vacuum period

Pressure period


Minimum average

net retention

Extended pressure period

Initial vacuum stage

Pressure stage Final vacuum stage

Applied vacuum

Period Applied pressure

Period Applied vacuum

Period

min min g/L kg/m3 min bar min bar min bar min

ADesired service life of 50 yearsc

Round:P and MR

30 60 30 120 120 Not recommended

Not recommended

Sawn: P and MRRound: R and ER

30 90 30 120 120 Not recommended

Not recommended

Sawn: R and ER 60 180 30 120 180 Not recommended

Not recommended


Round: P and MR

30 60 20d 100 60 Recommended 0.67 30 1 30 0.67 10

Sawn: P and MR 30 90 30 100 60 Recommended 0.67 30 1 30 0.67 10

Round: R and ER 30 90 30 100 90 Recommended Not recommended

Sawn: R and ER 60 180 30 100 120 Recommended Not recommended

NOTE 1 bar = 105 N/m2 = 105 Pa = 750 mm Hg. All pressures quoted are gauge pressures, i.e. relative to normal atmospheric pressure as zero.a P = permeable, MR = moderately resistant, R = resistant, ER = extremely resistant.b In consignments identified by the supplier as consisting of 80 % or more sapwood (class P and MR), excessive uptake of preservative is likely. In these instances a Lowry empty-cell process with the same pressure and final vacuum stages and solution concentration may be used.c Species with non-durable, resistant heartwood, e.g. spruces, are excluded from this performance category.d Lowry empty-cell process in accordance with BS 4072-2 may be used as an alternative using a solution concentration of 30 g/L.e See Table 2.



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Table 8 Preservative treatments for timber subject to intermittent wetting or damp conditions (hazard category 3e)Performance

categoryTimber form

and treatability

ratinga

Copper/chromium/arsenic by full-cell processb


Creosote by hot-and-cold

open tank process

PCP in heavy oil by double vacuum process Organic solvent preservatives by double vacuum process

Organic solvent preservativesd and creosote by

immersion process

Vacuum period

Pressure period


Minimum net

average retention

Extended pressure

period

Initial vacuum Pressure stage Final vacuum stage

Initial vacuum Pressure stage Final vacuum

Vacuum Period Pressure Period Vacuum Period Vacuum Period Pressure Period Vacuum Period

min min g/L kg/m3 min bar min bar min bar min bar min bar min bar min


Round: P and MR

30 60 30 110 60 Recommended 0.67 30 1 30 0.67 10 0.33 5 1 5 0.67 20 Not recommended

Sawn: P and MR greater than 20 mm thickness


Sawn: P and MR less than 20 mm thickness


Round: R and ER

30 90 30 110 120 Recommended Not recommended Not recommended Not recommended

Sawn: R and ER

60 180 30 110 120 Recommended Not recommended Not recommended Not recommended


Sawn or round: P and MR

30 60 20c 90 60 Recommended 0.5 10 1 10 0.83 10 0.33 3 0 3 0.67 20 Immersion time 10 min. Suitable for boards up to 20 mm thick only

Sawn or round: R and ER


0.83 10 2 15 0.83 20

NOTE 1 bar = 105 N/m2 = 105 Pa = 750 mm Hg. All pressures quoted are gauge pressures, i.e.relative to normal atmospheric pressure as zero.a P = permeable, MR = moderately resistant, R = resistant, ER = extremely resistant.b In consignments identified by the supplier as consisting of 80 % or more sapwood (class P and MR), excessive uptake of preservative is likely. In these instances a Lowry empty-cell process with the same pressure and final vacuum stages and solution concentration may be used.c Lowry empty-cell process in accordance with BS 4072-2 may be used as an alternative using a solution concentration of 30 g/L.d These treatments are restricted to woodwork of which the exposed surface will be painted or given some other protective finish which will be maintained in service.e See table 2.

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Section 4. Timber for use permanently or intermittently in contact with sea or fresh waterNOTE It is essential to read this section in conjunction with section 1.

28 GeneralThis section gives recommendations for the species, preservative treatment and other aspects of solid timber, generally in large dimensions, intended for use in locations in and around the British Isles in which it is permanently or intermittently immersed in sea water or fresh water. It does not cover the timber packing in cooling towers, which is dealt with in section 5.Examples of items covered by this section are as follows:

marine pilingstructural timbers in piers, jetties, quays, dolphins, etc.lock and dock gates and sluicesrevetments on inland waterwaystimber used in sea defence workswooden foundations and piers for bridgesstructural timbers in cooling towersship9s timbers

The choice of ship hull or superstructure timbers will be influenced by the working properties of individual species. For these items, where CCA water-borne preservatives are involved, post-treatment drying is essential before use in order to minimize movement after construction (see 6.2).

29 HazardsTimber for the fabrication of structures in fresh water can be subjected to severe and rapid attack by wood-rotting fungi. In sea water, particularly in warmer waters, there is the additional hazard of attack by marine boring organisms such as Limnoria spp and Teredo spp as well as decay by fungi.

30 PerformanceThe timber species and treatments in this section are intended to provide the maximum protection to timber in use. The service life is determined by the extent of fungal decay and marine borer attack, which depends on the severity of the conditions of exposure; in practice, such conditions can be very variable, particularly in the case of timber in sea water. The minimum life expected from preserved timber is as follows:

a) in fresh water: 30 years;b) in sea water: 15 years.

The life of a structure may however be limited by other factors such as mechanical damage or corrosion of fastenings.

31 Timber speciesTable 9 gives the suitability of timbers for use in permanent or intermittent contact with sea or fresh water.The timbers listed in column 1 of Table 9 may be used untreated. They have a high natural resistance to wood-rotting fungi, and also possess sufficient resistance to attack by marine borers to give a good performance in sea water in temperate countries. However, these timbers are not always readily obtainable. It is important to remember that it is only the heartwood of these timbers which is resistant to marine borers; the sapwood is usually very susceptible to attack and should be removed. Particular care should be taken with those timbers where the sapwood can easily be mistaken for heartwood and where a large proportion of sapwood can be present.In order to obtain the high and consistent standard of preservative treatment necessary where the timbers listed in column 3 of Table 9 are used in sea and fresh water, consideration should be given to using the timber in the round. The band of sapwood on the outside of round timber is normally much more permeable than the heart-wood and can be penetrated completely with a high loading of preservative. This can provide a much higher degree of protection than that to be expected from the limited preservative penetration often obtained in the heartwood of timber classed as resistant or extremely resistant.

32 Timber conditionThe timber before treatment should be in a suitable condition as recommended in 6.1.Large sections of timber of certain species which are difficult to impregnate with preservative (see Table 9) should be incised to the pattern laid down in BS 144-214) before treatment. In other cases, whilst incising is not necessary from the point of view of preservative penetration, it may be advantageous as a means of reducing the severity of splitting in service. Timber less than 75 mm thick should not be incised unless specifically requested by the purchaser.

14) In preparation. Pending publication, reference should be made to BS 913.



BS 5589:1989

BSI 04-1999 19

33 PreservativesThe following preservatives may be used. Their suitability for specific uses is given in Table 10.

a) CCA water-borne preservatives complying with BS 4072-1.b) Coal tar creosote complying with type 1 of BS 144-115) (high residue).


The treatment parameters are given in Table 10.

34.2 Full-cell process

CCA preservative solutions should be applied by the full-cell process in accordance with BS 4072-2.Creosote should be applied in accordance with BS 144-216). The end requirement of processes using creosote is specified in terms of a minimum average net retention and an extended pressure period.

Table 9 Suitability of timber for use in water

Table 10 Preservative treatment for timber for use in contact with water

15) In preparation. Pending publication, reference should be made to BS 144.16) In preparation. Pending publication, reference should be made to BS 913.

Species suitable for use untreated in sea water (hazard category Ma)

Species suitable for use untreated in fresh water (hazard category 4a)

Species suitable, if treated, for use in sea water (hazard category Ma) and

fresh water (hazard category 4a)

Afrormosia All timber rated as Beech

Andaman padauk very durable (VD)c Elm

Basralocusb Redwood or Scots pine

Ekkib American pitch pine

Greenheartb or Caribbean pitch pine

Iroko Douglas fir

Jarrah European larch

Kapur or Japanese larch

Okanb

Opepeba See Table 2.b Species generally believed to be the best for marine work.c See Table 3.

Timber species

Copper/chromium/arsenic by full-cell process


Fresh (hazard category 4a) and sea water (hazard category Ma)

Fresh water (hazard category 4a)

Sea water (hazard category Ma)

Vacuum period

Pressure period

Solution concentrationb

Minimum average net

retention


Minimum average net

retention


min min g/L kg/m3 min kg/m3 min

Redwood orScots pine 160 180 200 180Beech 160 120 400 180Douglas fir 60 180 50 160 180 180 240Pitch pine 160 180 200 180Larch 160 180 180 240Elm 160 120 200 180NOTE For sawn timber, incising before treatment is recommended for all species except beech and elm; heartwood of redwood need be incised only for use in sea water.a See Table 2.b Where high populations of Limnoria or Teredo are known to exist, it may be necessary to increase solution strengths.

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BS 5589:1989

20 BSI 04-1999

Section 5. Timber for use as packing in cooling towersNOTE It is essential to read this section in conjunction with section 1.

35 GeneralThis section gives recommendations for the species and preservative treatment of timber used for the small dimension packing timbers in water cooling towers. It applies to all cooling tower timbers with a minimum dimension of less than 50 mm, including splash bars, eliminator louvres, air-sealing walls, doors and door-frames, and packing support structures. It does not cover the species and treatment of the larger structural members of such towers, which are dealt with in section 4.For packing timbers, strict limitations are imposed on the timber species, the preservatives and the method of application.

36 HazardsIn view of the relatively small cross section of the packing timbers, attack by fungi, particularly soft rot fungi, is an extremely severe hazard in cooling towers. Failure of untreated timber in this environment, which is characterized by high moisture content and moderately high temperatures, can occur within a few years.

37 PerformanceCooling towers are normally required to give service for as many years as the plant with which they are associated. Chemical plant is normally written off after 10 to 15 years and electricity generating plant after 25 to 30 years.Two performance categories are therefore defined:


Evidence at present available suggests that, for the same treatment, the expected life with sea water is rather less than that with fresh water.

38 Timber species, quality and conditionRedwood (Pinus sylvestris) has proved satisfactory in practice and is the only timber which can be recommended.Before treatment the timber should be in a suitable condition as recommended in 6.1. In addition, the quality of the timber as regards knots, grain and other defects should comply with BS 4485-4.

Timber should be bundled in such a manner as to allow access of the solution to all its surfaces and to permit ease of handling.

39 PreservativesThe following two types of preservative may be used. Their suitability for specific uses is given in Table 11.

a) CCA water-borne preservatives complying with BS 4072-1.b) Coal tar creosote complying with type 1 of BS 144-117) (high residue).


The treatment parameters are given in Table 11.


CCA preservative solutions should be applied by the full-cell process in accordance with BS 4072-2.Creosote should be applied in accordance with BS 144-218). The end requirement of processes using creosote is specified in terms of a minimum average net retention and an extended pressure period.

41 Waste disposalWaste timber from cooling towers and other timbers treated with a solution of CCA with a concentration of 50 g/L or higher should not be disposed of by open burning on bonfires.NOTE For further information reference should be made to DOE Waste Management Paper No. 16 Wood Preserving Wastes.

17) In preparation. Pending publication, reference should be made to BS 144.18) In preparation. Pending publication, reference should be made to BS 913.



BS 5589:1989

BSI 04-1999 21

Table 11 Preservative treatments for European redwood timber for use in packing in cooling towers (hazard category 4a)


Copper/chromium/arsenic by full-cell process Creosote by pressure process

Fresh and sea water Fresh and sea water

Vacuum period

Pressure period Solution concentration

Minimum average net retention


min min g/L kg/m3 min


15 120 50 240 180


15 90 40 240 120

a See Table 2.

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BS 5589:1989

22 BSI 04-1999

Section 6. Fencing timber

NOTE It is essential to read this section in conjunction with section 1.

42 GeneralThis section gives recommendations for the species and preservative treatment of timber used for fencing with a life expectancy of 20 years or more in normal use. It does not describe the design or construction of wood fencing, but attention is drawn to BS 1722 which cover these aspects for different types of fences using wood components.This section defines two performance categories. It gives recommendations concerning the degree of natural durability which is necessary if timber is to perform satisfactorily without treatment, and concerning the preservative treatment which should be applied to achieve satisfactory performance with less durable timber, both in contact with the soil and not in contact with the soil.Experience has shown that fencing timbers often fail to give adequate service owing to inadequate drying prior to treatment. Procedures to be followed to ensure that timber is dry enough to be treated are reiterated and expanded upon in this section.Examples of items covered by this section are as follows:

fence posts, gateposts and strutsgravel boardsrailstimbers of gatesboarding and slatsdropperspost capsdowels

43 HazardsIn the UK, decay at the ground-line and in joints is the most common cause of failure in untreated wood fencing. Compared to ground-line hazards, timbers not in contact with the ground are subject to a lower fungal risk. The risk to fencing from insect attack is negligible.



Certain common species of timber grown in or imported into the UK have low natural durability and also react poorly to preservative treatment. These species are therefore only included in performance category B.

45 Timber species45.1 Timber not requiring treatment

The heartwood of the timber rated in accordance with Table 12 is sufficiently durable for wood fencing without preservative treatment. Whenever an amount of sapwood is present, the loss of which would render the commodity unfit for its intended use, the fencing components should be treated with preservative.

45.2 Timber requiring treatment

Timber species with a durability rating less than the appropriate rating shown in Table 12 for the desired performance category should be treated appropriately as described in clauses 47, 48 and 49.

Table 12 Timber with heartwood sufficiently durable to be used for fencing

without treatment

46 Timber condition46.1 General

The timber before treatment should be in a suitable condition as recommended in 6.1.

46.2 Moisture content

Moisture content should not exceed 28 % when measured with a calibrated moisture meter of the electrical resistance type, fitted with insulated probes that can be hammered into wood to the depth specified in Table 13.


Type of component

Timbers in ground contact, e.g. posts, struts, gravel boards (hazard category 4a)

Timbers not in ground contact, e.g. rails, gate timbers, boarding (hazard category 3a)


Very durable (VD)b




Moderately durable or better (MD, D or VD)b

a See Table 2.b See Table 3.



BS 5589:1989

BSI 04-1999 23

When determining the suitability of a charge of timber for preservation, moisture readings should be made on no fewer than (n/2) separate components, where n is the total number of components in the charge. The components to be measured should be taken from random positions in the charge. The number of heartwood and sapwood faces sampled should reflect the relative proportions of these types of wood in the charge as a whole.If preferred, the oven-dry method of determining moisture content as described in BS 5666-1 may be used in place of a moisture meter.To achieve the recommended moisture content of 28 % (m/m) timber can be either air dried or kiln dried. For either process it is essential that fencing timber is debarked and stacked so that air can circulate freely. In winter little natural drying is likely, therefore kiln drying may be the only effective solution.

46.3 Cutting after treatment

All cutting, drilling, profiling and shaping of the timber should be carried out before treatment. Under no circumstances should posts be cut near or below ground level after treatment. Any subsequently exposed surface should be treated with two liberal brush or spray applications of an appropriate preservative, recommended by the manufacturer; but it should be understood that this does not restore the full value of the original treatment and failure to comply with these recommendations can negate the value of the treatment.Table 13 Determination of moisture content

of timber to be treated for use in fencing

47 PreservativesThe following preservatives may be used. Their suitability for specific uses is given in Table 14 and Table 15.

a) CCA water-borne preservatives complying with BS 4072-1. The minimum concentration of solution recommended for this use is given in Table 14 and Table 15.b) Coal tar creosote complying with BS 144-119).c) PCP in heavy oil complying with BS 5707-2.d) Organic solvent preservatives complying with type F of BS 5707-1.

48 Limitations of preservativesReference should be made to 7.3 and 7.5 regarding corrosion of metal components and overpainting.


The treatment parameters required depend upon the performance category and wood species chosen. These are given in Table 14 and Table 15.


CCA preservative solutions should be applied by the full-cell process in accordance with BS 4072-2.Creosote should be applied in accordance with BS 144-220). Use of an empty-cell process is normally to be preferred for fencing timbers, except for resistant timbers. The end requirement of processes using creosote is specified in terms of a minimum average net retention and an extended pressure period.

49.3 Hot-and-cold open tank process

Creosote should be applied by the method described in BS 144-221).


The application of organic solvent preservatives and PCP in heavy oil by the double vacuum process should comply with BS 5707-3.

49.5 Immersion


Type of timber Length of electrodes w

Documents

BS5589 1989 Wood Preservation