Coating application in the fabrication factory(Image courtesy of Hempel UK Ltd.)HomePrint PDFSteelConstruction.infoThe free encyclopedia for UK steel construction informationBCSA TATA Steel SCI Steel KnowledgeLog in / create accountSearchViewsStandard corrosion protection systems for buildingsFrom Steelconstruction.infoThis article is designed to assist those responsible for either drafting corrosion protection specifications, or as contractors with arequirement to meet that which is specified. The information provided is based upon industrial experience, and is in the form ofcurrent practice tables of standard corrosion protection systems for steelwork in a range of environments.Contents1 Introduction2 Interior environments2.1 Hidden steelwork2.2 Visible steelwork2.3 Swimming pools3 Exterior environments4 Perimeter walls4.1 Steelwork in clear separation from outer leaf4.2 Steelwork in contact with outer leaf5 References6 Resources7 Further reading8 See also9 External links10 CPDIntroductionThe tables of standard systems for steelwork presented in this article relate to environment categories which are based upon thosegiven BS EN ISO 12944-2[1] and BS EN ISO 9223[2], which are described in the table below.Atmospheric corrosivity categories and examples of typical environments (BS EN ISO 12944-2[1])Corrosivitycategoryand riskLow-carbon steelThickness loss (m)aExamples of typical environments in a temperate climate (informative only)Exterior InteriorC1very low 1.3 -Heated buildings with clean atmospheres, e.g.offices, shops, schools, hotelsC2low> 1.3 to 25Atmospheres with low level of pollutionMostly rural areasUnheated buildings where condensation mayoccur, e.g. depots, sports hallsC3medium> 25 to 50Urban and industrial atmospheres,moderate sulphur dioxide pollutionCoastal area with low salinityProduction rooms with high humidity andsome air pollution e.g. food-processingplants, laundries, breweries, dairiesC4high> 50 to 80Industrial areas and coastal areas withmoderate salinityChemical plants, swimming pools, coastal,ship and boatyardsC5-Ivery high(industrial)> 80 to 200Industrial areas with high humidity andaggressive atmosphereBuildings or areas with almost permanentcondensation and high pollutionC5-Mvery high(marine)> 80 to 200 Coastal and offshore areas with high salinityBuildings or areas with almost permanentcondensation and high pollutionNotes:1m (1 micron) = 0.001mma The thickness loss values are after the first year of exposure. Losses may reduce over subsequent years.The loss values used for the corrosivity categories are identical to those given in BS EN ISO 9223[2].In coastal areas in hot, humid zones, the mass or thickness losses can exceed the limits of category C5-M. Special precautionsmust therefore be taken when selecting protective paint systems for structures in such areas.In many instances, steelwork will be in a warm dry interior where it will not corrode, and the structural stability of the building will notbe threatened during its design life (generally taken as 50 years). In such conditions (classified as C1) no corrosion coating isrequired. Examples include steelwork inside dry buildings with neutral atmospheres such as multi-storey office buildings, shops,schools, hotels, residential buildings, airport terminals, and hospitals, etc.However, when steelwork is exposed to moisture, corrosion will occur at a rate depending on the severity of the environment. Insuch cases, a coating system appropriate to the environment category should be provided. Note that some buildings may containareas where different environment conditions apply e.g. hospitals would normally be C1, but may contain kitchens and laundry areasthat would normally be C3. Some types of buildings, such as car parks may fall into any of the above categories or combinations ofthem depending upon their location, design and construction. Higher risk categories for interior environments (e.g. C4 and C5) arenot covered in this article and users are advised to seek specialist advice if their project involves such situations.The protective systems in the tables have unique identities. The film thicknesses given in the tables are nominal dry film values (m =micron = 0.001mm). The tables also identify the nearest equivalent system in BS EN ISO 12944-5[3] , and the required surfacepreparation to BS EN ISO 8501-1[4]Interior environmentsStandard systems for C2 low risk environment categoryIn deriving the protection systems described on these pages, the design life of building structures has been taken as 50 years. Thetables give two figures for durability:Structure life The period of reasonable freedom from severe corrosion of the steelwork that might lead to weakening of the structure.This figure assumes no mechanical damage in service that no maintenance is carried out and that up to 1mm of steel may be lost fromthe surface at the corrosion rate for each environment given in BS EN ISO 12944-2[1]. Visible steelwork will normally be accessiblefor maintenance and if repainting is carried out the quoted structure life will be extended.Coating life The expected period to maintenance of the protective coating. More frequent re-coating may often be preferred fordecorative reasons because of fading, contamination, wear and tear, etc. Hidden steelwork is assumed to be not accessible formaintenance, thus a figure for coating life of hidden steelwork systems is not applicable.Hidden steelworkStandard systems for C3 medium risk environment categoryNotes to tables:1.The thickness values given for primers are the total thickness used and may include a prefabrication primer. For example,80m can be in one coat or as 20m prefabrication primer plus 60m post-fabrication primer.2.For steel profiles over 6mm thick the minimum average thickness of galvanized coatings to BS EN ISO 1461[5] is 85m3.MIO - micaceous iron oxide.Visible steelworkStandard systems for C3 medium risk environment categoryStandard systems for C2 low risk environment categoryNotes to tables:Standard systems for C4 high risk environment category1.The thickness values given for primers are the total thickness used and may include a prefabrication primer. For example,80m can be in one coat or as 20m prefabrication primer plus 60m post fabrication primer.2.A wetting low viscosity primer is recommended to obtain satisfactory performance.3.For steel profiles over 6mm thick the minimum average thickness of galvanized coatings to BS EN ISO 1461[5] is 85m.4.To enhance durability and improve the aesthetic appearance, the hot-dip galvanized coating can be treated with a mordantwash or T wash followed by a vinyl primer at 40m and a vinyl finish at 60m.5.MIO - micaceous iron oxide.Swimming poolsNotes to table:1.The Coating Life is estimated for the paint system only and does not include the hot-dip galvanized coating. The life of the totalprotection system without maintenance should exceed 25 years, however, it is anticipated that for aesthetic reasonsmaintenance will be carried out at periods of 10 years or less.2.For steel profiles over 6mm thick the minimum average thickness of galvanized coatings to BS EN ISO 1461[5] is 85m. Forhidden steelwork, e.g. behind a suspended ceiling, no further treatment is required. For steelwork that is visible, the galvanizedcoating should be surface treated and coated as shown.3.Methods of preparing hot-dip galvanized coatings need to ensure that a satisfactory condition is achieved to accept a paintcoating system. It is important that the steelwork is thoroughly degreased and free from any contamination. Several methodscan be considered including:1.Mordant wash or 'T' wash, which is the brush application of a chemical solution that reacts with the galvanizedsurface. The effectiveness of the solution is readily visible and untreated areas are self evident. After treatment, thesolution should be rinsed off with clean water and then the treated surface dried ready for painting. It is important thatthe manufacturers' instructions are carefully followed to ensure successful results.2.Etch primers, which can be either single or two pack materials and they are applied as thin film coatings to aroundStandard systems for C4 high risk environment categoryStandard systems for C3 medium risk environment category10m to 25m in thickness. The two pack versions tend to provide an improved surface compared with the single pack3.Sweep blasting, which is the use of low pressure fine grade non-metallic abrasive which can be very effective butrequires care and expertise. The treatment should slightly roughen the galvanized surface without removing the coating.4.MIO - micaceous iron oxide.Exterior environmentsCoating system durability given in the following tables is based on practical experience. It is the expected life, in years, before firstmajor maintenance. This is taken as degradation level Ri3 from BS EN ISO 4628-3[6] (1% of surface area rusted). It should benoted that this does not imply a guarantee of life expectancy. The durability of galvanized steelwork is derived from the figures in BSEN ISO 14713[7].Standard systems for C5 very high risk environment categoryNotes to tables:1.For steel profiles over 6mm thick the minimum average thickness of galvanized coatings to BS EN ISO 1461[5] is 85m.2.Where painting of galvanized steelwork is required for aesthetic or other reasons; suitable systems from BS EN ISO 12944-5[3] may be used.3.The thickness values given for primers are the total thickness used and may include a prefabrication primer. For example,80m can be in one coat or as 20m prefabrication primer plus 60m post fabrication primer.4.MIO - micaceous iron oxide.5.It should be noted that the colour range of MIO is limited.6.The zinc rich primer applied at 80m would increase the durability of the system by approximately 5 years.7.The primer coat may be omitted providing the build/intermediate coat is applied directly to a clean steel substrate of suitablesurface profile.8.With time, elastomeric urethanes may suffer from superficial degradation known as chalking which changes the visualappearance but does not affect the over all durability of the system. Where colour stabilization is required for appearancepurposes, this can be achieved by the application of the finish coat in this system.9.The protection of structural steelwork against atmospheric corrosion by thermal sprayed aluminium or zinc coatings is coveredin BS EN ISO 2063[8].Perimeter wallsSteelwork in clear separation from outer leafFor wall cavities in which steel will remaindry, either by use of an impermeable outerleaf or where there is physical separation ofthe steel from the outer leaf, a system fromthe Hidden steelwork section forenvironment categories C1, C2 or C3 maybe appropriate. The treatment specified forcavity wall condition should also be suitablefor the interior environment of the building.Should the internal environment be moreaggressive, additional protection will berequired.Notes to table1.The thickness values given for primers are the total thickness used and may include a prefabrication primer. For example,80m can be in one coat or as 20m prefabrication primer plus 60m post-fabrication primer.2.The environment within a normal cavity wall construction is categorised as being C2. The system PW-C2-S is consideredappropriate for such conditions. However, where steelwork within the cavity is deemed to be in a more aggressiveenvironment category, the application of a high build bitumen coating at 150m to the faces of the steelwork within the cavitymay be applied before or during construction.Steelwork in contact with outer leafBrickwork cladding or other masonry, can develop cracks and leakage over time. When steelwork is in contact with, or embeddedin a brick/masonry outer leaf, one of the following systems should be used. In some regions, stainless steel may be required forembedded members by local regulations or be deemed necessary to provide adequate durability. Specialist advice should be sought.References1.^ 1.0 1.1 1.2 BS EN ISO 12944-2: 1998, Paints andvarnishes Corrosion protection of steel structures byprotective paint systems Part 2: Classification ofenvironments, BSI2.^ 2.0 2.1 BS EN ISO 9223: 2012, Corrosion of metals andalloys Corrosivity of atmospheres Classification, BSI3.^ 3.0 3.1 BS EN ISO 12944-5: 2007, Paints and varnishes Corrosion protection of steel structures by protective paintsystems Part 5: Protective paint systems, BSI4.^ BS EN ISO 8501-1: 2007, Preparation of steelsubstrates before application of paints and related products.Visual assessment of surface cleanliness. Rust grades andpreparation grades of uncoated steel substrates and ofsubstrates after overall removal of previous coatings, BSI5.^ 5.0 5.1 5.2 5.3 BS EN ISO 1461: 2009, Hot dip galvanizedcoatings on fabricated iron and steel articles. Specifications and test methods. BSI6.^ BS EN ISO 4628-3: 2003 Paints and varnishes - Evaluation of degradation of coatings - Designation of quantity and size ofdefects, and of intensity of uniform changes in appearance - Part 3: Assessment of degree of rusting. BSI7.^ BS EN ISO 14713-1: 2009 Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron andsteel in structures. General principles of design and corrosion resistance. BSI8.^ BS EN ISO 2063: 2005, Thermal spraying - Metallic and other inorganic coatings - Zinc, aluminium and their alloys, BSIResourcesHendy, C.R.; Iles, D.C. (2010) Steel Bridge Group: Guidance Notes on best practice in steel bridge construction (5th Issue).(P185). SCIGuidance Note 8.01 Preparing for effective corrosion protectionGuidance Note 8.03 Hot dip galvanizingGuidance Note 8.04 Thermally sprayed metal coatingsGuidance Note 8.05 High performance paint coatingsSteel Buildings, 2003, The British Constructional Steelwork Association Ltd.Chapter 12 Corrosion ProtectionFurther readingD.Deacon & R.Hudson (2012), Steel Designers Manual (7th Edition), Chapter 36 - Corrosion and corrosion prevention, TheSteel Construction Institute.D.A. Bayliss & D.H.Deacon (2002), Steelwork Corrosion Control (2nd edition), Spon Press.See alsoCorrosion of structural steelInfluence of design on corrosionSurface preparationPaint coatingsMetallic coatingsAppropriate specificationsInspection and quality controlExternal linksBritish Coatings Federation (http://www.coatings.org.uk)Galvanizers Association (http://www.galvanizing.org.uk)Paint Research Association (http://www.pra-world.com)The Thermal Spraying and Surface Engineering Association (http://www.tssea.co.uk)CPDCorrosion protectionRetrieved from "http://www.steelconstruction.info/Standard_corrosion_protection_systems_for_buildings"Category: Corrosion protectionSitemapContactCookies