CHAPTER 7

BRICKWORK: CAVITY WALLS,

PAVING & BEAM FILLING

Introduction:

• Cavity walls consist of 2 separate wall of brickwork or concrete blocks (called skins or leaves)

built next to each other with a 50mm space (cavity) between them.

• Masonry is an absorbent material that will draw rainwater or humidity into the wall from both

the inside and outside surfaces.

• The cavity serves to drain water through weep holes at the base of the wall or above the

windows.

• The weep holes allow to create an air current that removes evaporated water from the cavity.

• Weep holes are placed above windows to prevent dry rot damage to the window frames.

• Please look at the table on page 98 for the advantages and disadvantages of cavity walls and

also copy this in your books.

1.1) Construction of cavity walls:

The following regulations must be met when cavity walls are constructed:

• The space between the skins must be 50mm wide and may never exceed 100mm.

• The skins (leaves) must be 110mm thick.

• The walls must be built in a firm bond; the units and courses must be joined using mortar.

• The skins must be connected using wall ties that are set apart 900mm horizontally and 450mm

vertically, as close as possible to any opening. Wall ties must also be placed at 300mm intervals

along the junctions and openings of the wall.

• Except for the wall ties, any contact between the 2walls must be avoided.

• Weep holes must be inserted under the horizontal damp-proof coursing as well as above the

damp-proof coursing over the opening.

• Wall ties must be rust-free amd must prevent the penetration of rainwater.

• If wall ties are used on inner and outer skins that have uneven mortar joints, they may cause

rainwater to run down the inner skin.

• The cavity between the walls must be kept clear of mortar when bricks are lain.

• Mortar must be removed from the wall ties, since it may cause seepage of water to the internal

wall (capillary action)

• In parapet wall, the cavity must be maintained right up to the coping level.

• Cavity walls must be restricted to a length of 8m and height of 3m. This has to be considered in

the design.

• Restrict gables to a height of 5m.

• During construction, provision must be make for inspection holes to allow the removal of wasted

mortar. These holes have to be sealed when the construction is complete.

• Openings that are connected by brick bonds do not require wall ties.

• Any bridging of the cavity, excluding the wall ties, must be provided with damp-proofing

coursing.

• No wall ties may be placed on the damp-proof coursing.

• Damp-proof coursing must be laid 150mm above ground level.

• Use lateral supports along the length of long cavity walls during construction.

• Ventilating bricks must be placed in the bottom course of the external walls in very wet regions.

• In ordinary weather conditions, a joint must be inserted at 1m intervals.

Locations of the weep holes:

The weep hole must be located above the horizontal damp-proof course of the external part of

the wall.

Purpose of the weep holes:

It allows water that penetrates the outside wall to drain out.

Purpose of the cavity between walls:

• The cavity will ensure that no water will penetrate the inner wall.

• The cavity provides insulation against heat.

• The cavity provides insulation against cold.

• The cavity provides insulation against sound.

• Please inspect and look carefully at Figures 7.1 (pg. 99), 7.2 & 7.3 (pg. 100), 7.4 & 7.5 (pg.

101), and 7.6 (pg. 102).

• Do activity 7.1 on page 103.

1.2) Paving:

Paving can be described as an outdoor floor or a surface covering. The following materials can be

used for the paving process:

• Asphalt

• Concrete

• Stone (flagstone, cobble stone and artificial stone)

• Brick

• Brick tiles.

Brick paving is normally used as a decorative method to create an outdoor floor or surface. The

advantage of using bricks rather than other materials is that individual bricks can be lifted and

replaced. This allowed repair work to be carried out under the paved surface without visible signs

of damage once the paving bricks have been replaced.

The following areas can be covered:

• Pavements and Patios.

• Town centres and Road surfaces.

1.3) Terminology associated with paving:

Paving contractors require special knowledge regarding excavations, soil preparation and laying

methods. Specific terms are used to refer to the various aspects associated with paving:

• Subgrade: The natural earth (soil) on which the paving will be laid and which

has to be prepared.

• Sub-base (natural earth): The prepared layer beneath the paving and bedding sand.

• Sub-base stabilisation: Where necessary, this should be done in accordance with SANS

specifications (requires cement to be mixed into the sub-base).

• Bedding sand: The final layer upon which the paving units are laid.

• Jointing: River sand is used as grouting between paving blocks.

• Earthworks: The preparation of the sub-base.

• Soil conditions: Appropriate application will determine if special subsoil is required.

This may involve excavation and backfilling.

• Walkways: paving subjected to only pedestrians – a good quality natural soil

will provide satisfactory strength for the installation of paving.

However, paving which will last a lifetime requires an imparted sub-

base.

• Sandy and clay soil: Such conditions require a specially designed sub-base.

1.4) Ground Preparation:

Earthworks or sub-base preparation is site specific and fall within the scope of an engineer’s field

of expertise. It is strongly recommended that an engineer plan paving earthworks.

Determine the max height that the pavers should reach. Remember that the slab should always

slope downwards, away from the building, to allow water drainage. Calculate the total depth of

the excavation by adding the thickness of the base, bedding and paving brick.

• Depending on the size of the area to be paved, a shovel or a mini-excavator can be used. The

equipment used depends on the existing surfaces. The are must be excavated to the depth of

stable soil, removing all loos sand.

• If soft spots in the soil are still found, further excavation may be required. These spots can also

be filled and compacted with sub-base material.

• The ground below the paving must be firm and stable to ensure that it does not settle unevenly.

• Remove all waste material as well as roots and vegetable matter from the soil.

• Finish the area to the correct level and slope. A minimum slope of 2% in any direction is

required.

• Make sure there are no furrows to prevent the pooling of water that can infiltrate the layers.

• Soft areas and areas that have been filled must be compacted well. A plate compactor or a

hand stamper can be used. If the filling is very dry, add a little water prior to compaction.

• Recheck surface levels and slopes and correct them if necessary.

1.5) Preparing the sub-base:

When the excavation is complete and the soil had been compacted, the next step is the laying of

the base material. The sub-base usually consists of crushed stone with sharp edges. The size of the

stones and the sharp edges make the compaction process easy. The thickness of the sub-base

depends on the planned used and the weight that will be placed on the paved area. If the

subgrade is soft clay, a thicker layer will be required.

• Spread the crushed gravel over the area in an even layer.

• Once the sub-base material is evenly spread, use a plate compactor and compact the area

several times.

• Ensure that the compacted gravel is level, sloped and in line with the calculated height.

• Spread a layer of loose sand (crusher dust) 25mm thick over the sub-base and level it off.

1.6) Paving methods:

Brick, concrete, permeable, interlocking and stone pavers are popular paving options for outdoor

areas, walkways, driveways, ect. There are trhee basic paving methods for these types of pavers,

depending on the traffic bearing applications:

• Dry-laid or sand set,

• Bitumen-set &

• Mortar-set.

The dry-laid and mortar-set methods will be discussed in this course.

1.6.1) Dry-laid paving:

This method is the least expensive option. The pavers are laid in a sand bedding and sand is swept

into the paver joints to fill the joints. It is important that fine-grained sand is used for this purpose.

This process also helps to secure the pavers into place. The pavers are then compacted again until

the joints are full.

Prepare the area to be paved as set out above:

• Excavate the soil to a depth of approximately 150mm where required.

• The area should be graded to achieve the best slope for drainage, having considered existing

conditions and paving tolerances.

• Wet the area to its optimum moisture level and compact it thoroughly.

• Do not use plastic sheeting beneath or on top of bedding sand. (It does not stop weeds from

growing and negatively affects the structural integrity of paving units)

• Bedding sand must be spread over the sub-base and screeded in the loose condition to ensure

an even thickness of approximately 20 to 30mm. Use river sand or crusher dust to provide a

smooth surface to receive the paving.

• The bedding sand must be moist but not saturated.

• The paving block can now be hand-packed in the desired pattern.

• Whole paving block must be laid first. Accurately cut pieces should then be fitted into the gaps

(e.g. around manholes or gulleys)

• Mark the pavers for cutting when they are packed and then cut them individually, using a pave

cutter or masonry saw with a diamond tipped blade.

• All exposed edges must be suitably retained by using edge restraints (as discussed later in this

chapter).

• Compaction of pavers should take place while the bedding sand is still moist.

• Jointing sand (mixture of plaster sand and cement) should be swept into the gaps between the

pavers before compacting, as this will prevent the edges from chipping.

• Sand that complies with sieve analysis as specified by SANS must be used. The jointing sand

must be swept into the joints until they are filled.

• Compaction must take place in such a way that a uniform, even surface is obtained over the

entire paved area.

• This procedure must be repeated until the joints remain full.

• Damage to pavers can be avoided by fixing conveyer belting onto the base of the plate

compactor.

• Check and adjust lines after compaction, using a special alignment tool.

• More sand should be swept into the paving joints after a week has passed.

• Remove all rubble after completion of work.

• Check and adjust lines after compaction, using a special alignment tool.

• More sand should be swept into the paving joints after a week has passed.

• Remove all rubble after completion of work.

Have a look, and copy the advantages and disadvantages table for Dry-laid paving on page

106 into your books

1.6.2) Mortar-set paving:

Mortar-set pavers are permanently fixe in place and require little long-term maintenance.

Follow the step set out for the preparation of the ground.

• Excavate soil to a depth of approximately 150mm where required.

• The area should be graded to achieve the best slope for drainage, having considered the

existing conditions and paving tolerances.

• Wet the area to its optimum moisture level and compact it thoroughly.

• A damp-proof membrane can be laid on the sub-base to prevent plants/weeds from growing

through the paving joints.

• Cover the area with a layer of river sand to provide a smooth surface to receive the concrete

base as well as to avoid soil movement.

• The concrete base is now placed and properly cured for 28 days. In South Africa, it is common

practice to grout paving with cement slurry.

• A thick bed or thin bed method can be used for this application.

• Mortar-set pavers are now permanently fixed in place and require minimum long-term

maintenance.

Look at, and copy into your book, the advantanges and disadvantages of mortar-set paving.

1.7) Paving tips:

• Excavated material needs to be removed from the site.

• If there are any natural depressions in the area to be paved, they have to be filled with special

material. For residential driveways, excavated earth can be used. Bedding sand should never

be used for this purpose.

• Consider the roots of trees that will grow under the paving.

• Consider the underground utilities when excavations are done.

• After excavation, drainage levels should be check and rectified if necessary.

• Bedding sand must laid in advance of the placement of paving only if that area of paving can

be completed on the same day.

• Never compact the bedding sand before the paving blocks are laid. If it is compacted

accidentally before the units are laid, it must be raked and rescreeded in a loose condition.

• Bedding sand must be moist. If it dries out, it must be raked into a heap, moistened and levelled

and screeded again.

• If too little or too dry bedding sand is used:

- the paving surface will be uneven

- pavers will rock (move) and eventually break

- grout will erode

• Lay the paving units on the bedding sand and tap each one firmly into place with a wooden or

rubber mallet.

• In practice, pavers are often laid out, marked for cutting, and then cut on the ground with an

angle grinder. However, the cutting is often not as accurate and neat as required. A masonry

saw or pave cutter should preferably be used.

1.8) Paving failures:

• Paving failures are caused by the penetration of water into the earthworks beneath the paving.

Good drainage will eliminate this problem.

• Make sure there are adequate longitudinal falls/slopes and no furrows to prevent the

infiltration of water into the layers. A minimum fall of 2% in any direction is required.

• Ensure that the paving is laid 5-10mm higher than storm water structures or channels.

• If a high water table exists, subsoil drainage should be installed.

• Drainage channels and underground drainage pipes should be installed in certain areas (e.g.

low points in steep driveways and around downpipes).

• In-situ concrete on edges is not recommended because it normally crumbles after a few months.

1.9) Laying of paving blocks:

• Lines must be set up at right angles to control the placement of the paving blocks.

• Joint widths should be between 2mm and 6mm.

• Nibs on pavers should be between 1mm and 2mm. Use nylon line as guides and leave grouting

gaps larger than paver nibs.

• In South Africa, brick pavers are joined with nibs touching adjacent pavers.

• Pavers from different packs should be mixed when installation takes place.

• Pavers must be transported in a paving cart or wheelbarrow lined with blankets.

• Avoid throwing pavers into wheelbarrows and frontend loaders, as this will damage the pavers.

1.10) Retaining edges:

Retaining edges are necessary for the maintenance of the paved area.

If edging is not installed, the pavers will move around and separate.

Severe weather conditions and heavy traffic along with no edge restraints will ruin the paved

surface.

Edge restraints (finishing):

• Earth preparation should extend to the rear face (back edge) of the edge limits.

• Edge restraints consisting of kerbs and channels have to be constructed on the sub-base before

the paving blocks are laid. In residential applications, an edge restraint is constructed by laying

the paving blocks along the edge in a concrete bed (header course is generally used.)

• The best edge restraints are kerbs. For residential and pedestrian applications, garden kerbs

are good enough.

• Large paved areas as well as the paving of steep sloped may require restraints in the form of

edge beams.

The purpose of a retaining edge is to withstand the lateral pressures applied by the paving as

well as any traffic.

There are different ways to achieve this, but the most commonly used method is a mass concrete

bed and haunch (concrete edge).

The concrete bed will keep the edge unit in place and maintain a level surface.

It also adds weight to the retaining structure.

The haunch (concrete side) will keep the edge units in position, in terms of the lateral movement of

the pavers, and will also add weight to the retaining structure.

The bedding for the edge course must not be less than 75mm.

This can be reduced when the edge course is not a retaining edge.

Where the edge course carries heavy traffic or vehicles (public footpath, highway or entrance to a

garage), the recommended bedding should not be less than 100mm.

The haunch must not be less than 75mm wide and should extend to 15-25mm from the top surface.

Please look carefully at Figures 7.7 – 7.13 on pages 109-110.

1.11) Reasons for construction failure:

The structure does not comply with the specifications set out by SANS when:

• The concrete haunch is too thin to support itself and cracks or crumbles under pressure.

• There is too little weight to retain the structure and keep the paving in place.

• The bond between the haunch and the edge units is weak and will easily crumble.

• The sub-base is not contained and will be washed out by groundwater.

1.12) Please have a look at the two main different paving patterns mostly used in South Africa

illustrated in Figures 7.14 & 7.15 on page 111.

Then, do activity 7.2 on page 111

2) Beam filling:

Beam filling is a filling of brick between the roof timber, from wall plate to roof covering, to

prevent the entry of birds and vermin and to render the wall watertight.

Beam filling refers to the brickwork that is used on the exterior half of the external wall of a

building when the final height has been reached. This brickwork is laid between the lower sides of

the roof trusses up to the roof covering. It covers the joints between the roof trusses and the wall

finish as well as the spaces between the rafters.

2.1) Purpose of beam filling:

The purpose of beam filling is to fill the spaces between the roofing rafters or joists from the wall

plate to the roof covering with brickwork. This is done for the following reasons:

• Keep out insects,

• Prevent wind from blowing in under the roof.

• Prevent birds from nesting/perching in the roof.

• Improve the stability of the roofing rafters.

Copy the advantages and disadvantages table for beam filling on page 112 into your books.

2.2) Construction detail:

Beam filling refers to brickwork that is used on the exterior half of the external wall of a building

when the final wall height has been reached. This brickwork is laid between the lowersides of the

roof trusses and the roof covering.

• Beam filling is used between the rafters and roof trusses.

• The construction takes place after the roof trusses have been placed in position.

• The brickwork is the same height as the roof batten.

• It is usually a half-brick wall (110mm).

• The height of the beam filling is indicated by the number of brick courses: e.g. two, three, ect., or

by the height – 75mm (height of one brick), 150mm (two bricks) and 225mm (three brick

courses)

Have a look at Figures 7.16, 7.17 and 7.18 on pages 113 and 114.

Thereafter, please do activity 7.3 on page114.