SUPERSTRUCTURE

Aggregate

Aggregates is the term used for the sand or stone pieces that can be mixed with cement and water to make concrete or mortar.

Arch

An arrangement of bricks over an opening.

Arris

The sharp edges of a brick.

Bat

A portion of an ordinary brick with the cut made across the width of the brick (½ bat, ¾ bat and bevelled bat).

Beam filling

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 weather tight.

Bed

The lower rectangular surface of a brick when placed in position; usually 222 x 106mm.

Brickforce

Light welded material made up of two hard drawn wires (not less than 2.8mm in diameter, not bigger than 3.55mm in diameter), joined at regular intervals either at right angles (ladder) or diagonally (truss type) cross wires. The most commonly used type is the ladder type.

Bed joints

Mortar joints parallel to the beds of the bricks, and therefore usually horizontal in general walling; thickness from 3 to 12mm.

Brick gauge

The height of a brick course.

Broken bond

The use of part bricks to make a good bonding pattern where dimensions do not allow regularised bond patterns of full bricks.

Bull nose

A bullnose is used for copings, or in such positions where rounded corners are preferred to sharp arrises, e.g. window sills.

Butt-joint

A joint between two square-ended pieces of the same thickness without overlap.

Cavity wall

Wall of two leaves effectively tied together with wall ties, with a space between them, usually at least 50mm wide.

Chases

Recesses cut in walls to accommodate service cables or pipes.

Closer

A portion of an ordinary brick with the cut made longitudinally, and usually having one uncut stretcher face.

Compressive strength

The average value of the crushing strengths of a sample of bricks or concrete, tested to assess load bearing capability.

Control Joint

A joint designed to allow sections of a structure or wall to move in a consistent line without weakening the functional reliability of the structure or wall.

Coping

The materials or masonry units used to form a cap or finish on top of wall, pier, or chimney, to protect the masonry below from water penetration. Commonly extended beyond the wall face and incorporating a drip.

Corbel

A feature, or course, or courses of brick projecting from the face of the wall.

Course

One complete level row of bricks in brickwork.

Damp-proof course (DPC)

A course or layer of impervious material which prevents vertical movement of water.

Datum

A fixed reference point from which levels are set out.

Drawing or plans

A construction drawing showing a view of a building or object in a horizontal plane. A floor plan shows the floor area of the building or object in a horizontal plane.

Dumpy Level

A dumpy level is an instrument used in surveying and building to set horizontal heights/levels. The instrument requires to be set level (using a spirit level) in each quadrant, to ensure it is accurate through a full 360° traverse. As an alternative,
laser levels have been developed to provide the same height transfer purpose.

Durability

The ability of materials to withstand the potentially destructive action of natural conditions and chemical reactions.

Efflorescence

The unsightly chalk-like appearance on a building due to the crystallisation of soluble salts contained in the bricks or mortar.

Expanded Polystyrene (EPS)

EPS is used for thermal insulation in foundation walls and floor slabs (SOG [Slab on ground]) as sheets or boards. Loose beads of EPS can also be used as an aggregate for lightweight concrete, plaster or renderings. EPS can also be used for permanent formwork, prefabricated and foundation walls, under floor heating and drainage boards.

Face work

A surface of a brick, such as the header face and stretcher face. The term is also applied to an exposed surface of a wall, which is built neatly and evenly without an applied finish.

Frog

A shallow, sinking formed on either side or both of the 222 x 106mm faces of a brick. A wire-cut brick has no frogs; a pressed brick has two frogs as a rule. A frog provides a good key for the mortar.

Gables

Portion of wall above eaves level that enclosed the end of a pitched roof.

Gauge rod

Batten marked at intervals for vertical setting-out of brick courses.

Gauge boxes

Boxes of specific volumes to accurately measure the proportions of cement, and sand when preparing to mix mortar.

Header

The end surface of a brick; usually 106 x 73mm

Jointing

The finishing off of joints between courses of masonry units before the mortar has hardened.

Lap

The horizontal distance which one bricks projects beyond a vertical joint in the course immediately above or below it.

Lintel

A formed concrete element (which has tensile wires to give it strength, spanning an opening in a wall (e.g. above a door or window frame) to carry the superimposed load.

Lug

A metal fastener that projects out and has a hole in the end for a screw, nail or other fixing for building in. Usually used for building in a window and door frames.

Mortar (dagga)

A specific mix of sand, cement and water, used for bricklaying and plaster.

Movement joint

A continuous horizontal or vertical joint in brickwork filled with compressible material to accommodate movement due to moisture, thermal or structural effects.

Parapet

A low wall around the perimeter of a building at roof level or around balconies.

Pier

A vertical block of brickwork which may either be isolated or attached to the face of a wall.

(Extract from SABS 1090: Aggregates from natural sources – fine aggregate for plaster and mortar)

Workability

Workability is a property which describes how easily mortar can be spread over the masonry unit and affects the performance and the productivity of the artisan. In almost all cases there is a specific mortar, which will best suit the project and the required workability; for example, the type of masonry unit, degree of exposure, local aggregate, and season, will all affect the workability.

Lime

The use of lime in mortar mixes is optional. Lime imparts the properties of plasticity and water retention to mortar. The latter property is important as it prevents mortar drying out, resulting in the incomplete hydration of the common cement.

Lime used in mortar is hydrated lime (commercial bedding lime) complying with SABS 523:1999; and not quicklime or agricultural lime. Lime gives the best results when used with coarse sands. Lime with clayey sands can make the mortar over-cohesive and difficult to use.

Lime should be used if the sand lacks fine material or is single sized, as such sands tend to produce mortar with poor workability unless lime is included in the mix.

Lime also helps the fresh mortar to retain water when it is spread against dry cement bricks or blocks and helps to prevent cracking of the hardened mortar. A maximum of 40ℓ of lime is permitted per 50 kg of cement.

Note: Do not use lime with masonry cement.

Mortar plasticisers

Mortar plasticisers exercise a desirable effect on the workability and plasticity of the mortar in which they are used. Generally, the admixtures have no effect on setting time (they do not accelerate or retard the mortar setting) but may cause air entrainment.

The use of mortar plasticisers is optional. Their effectiveness varies with the quality of sand, the composition of the cement, its fineness, the water-cement ratio, temperature of the mortar, volume of plasticiser and other factors or site conditions.

Modular co-ordination

Modular co-ordination is a method of co-ordinating the dimensions of buildings and building components to reduce the range of sizes required and to enable components to be built in on site without modification. For modular co-ordination, the dimensions of components and the space to be filled by them must be related to a single denominator, the basic module. The South African Bureau of Standards has accepted 100 mm as the basic module for horizontal and vertical dimensions. Buildings should be dimensioned to incorporate controlling dimensions which provide for the necessary co-ordination of dimensions to accommodate all modular size components, assemblies and units.

Setting out is simplified because most dimensions will be multiples of 100mm, though with concrete block masonry a 200mm module is preferable. Furthermore brick and block sizes need to have dimensions that provide the ideal width for the human hand to lift and place with the minimum of strain as well as allowing the bricks and blocks to be bonded in any direction.

The most commonly used and manufactured brick size is the “Imperial Brick”; with the following nominal dimensions – 222 mm long x 106 mm wide x 73 mm high- see figure 13.1. The use of modular size masonry units is essential if buildings are designed to the 100mm standard module – as stated in SANS 993 modular co-ordination in building. Modular planning is based on a nominal joint thickness of 10-12mm. Modular wall thicknesses are 90,106,140 and 190mm. Several sizes of bricks and blocks are made by individual manufacturers.

Various combinations of these dimensions are illustrated in the table on the following page. Non-modular sizes of units are found in practice not to bond well without considerable cutting of the units. English or Flemish bond and construction of square brick piers is not possible as such units deviate from the basic principle of masonry bonding where the length of a unit should be twice its width plus the thickness of the bedding or perpendicular joint. Generally, for easier, cost effective and sound building practice, the unit size should be based on the principles of modular co-ordination as per the table.

Bricks

Most bricks are usually manufactured to the imperial size 222 mm (i.e. 2 modules) horizontal and 106mm (1 module) vertical. There is a rough arithmetical relationship of length to width of 2:1 and length to height of 3:1 in the standard or imperial brick of 222mm long x 106mm wide x 73mm high and when used with a recommend 12mm mortar joint, the following formats can be used:

• The format size becomes 234 x 118 x 85mm.
• The format length (234) is the spacing of stretche perpends.
• The format width (118) is the spacing of header perpends
• The format height (85) is the coursing height.

Blocks

The most popular co-ordinating block dimension is 400 mm (i.e. 4 modules) horizontal and 200 mm (2 modules) vertical. To make up the design lengths and heights it may be necessary to use, other than the basic size block, blocks having co-ordinating lengths of 100, 200 and 300mm and a co-ordinating height of 100mm. These sizes may be achieved by using specific blocks of suitable modular dimensions. If a unit is of modular dimensions, and is so described, it will fit into a modular space on the design grid.

Properties

Size

Size varies depending on category, type and the manufacturing process. When describing the dimensions of a masonry unit, the standard procedure is length x width x height (all in millimetres).

Water absorption

Water absorption is the percentage increase in the weight of a dry masonry unit when it has been saturated. It is one of the parameters for definition of engineering bricks and damp-proof-course bricks. It affects rain penetration through the outer skin of a wall (typically in a cavity wall) and is used to define the flexural strength in lateral load design. The water absorption test requires a masonry unit to be soaked in a bath of water for 24 hours to determine its ability to absorb water. Depending on the type of masonry unit, this will range from 5% to 15%. The more porous the unit, the more water it can absorb.

Water absorption of masonry units is not specified in SANS 1215. It is not regarded as a significant characteristic where weather conditions in South Africa are mild and where freezing and thawing seldom occur. Water absorption is a measure of water absorbed in a masonry unit and does not necessarily measure or describe the porosity or permeability of a unit.

Efflorescence

Efflorescence is harmless and usually temporary. It can be minimized by protecting masonry units from rain at the early stage of construction and normally takes one of three forms: lime bloom; lime weeping; and crystallisation of soluble salts.

Lime bloom

The most common form of efflorescence is lime bloom and it is particularly noticeable on coloured masonry units. It is a white deposit which is apparent either as white patches or as an overall lightening in colour. The latter effect is sometimes mistakenly interpreted as the colour fading or being washed out. The cause of lime bloom lies in the chemical composition of cement. When water is added to cement, a series of chemical reactions take place which result in setting and hardening. One product of these reactions is “lime” in the form of calcium hydroxide. Calcium hydroxide is slightly soluble in water and, under certain conditions, can migrate through damp concrete or mortar to the surface and there react with carbon dioxide from the atmosphere to produce a surface deposit of calcium carbonate crystals.

This surface deposit is similar to a very thin coat of whitewash and gives rise to the white patches or lightening of colour mentioned previously. The surface deposit is normally extremely thin and this thinness is demonstrated by the fact that, when the masonry unit or mortar is wetted, the film of water on the surface usually makes the deposit transparent and the efflorescence seemingly disappears. The occurrence of lime bloom tends to be spasmodic and unpredictable. Nonetheless, an important factor is the weather. Lime bloom forms most readily when masonry units or mortar becomes wet and remains damp for several days, and this is reflected in the fact that is occurs most frequently during the winter months. Extended periods of rain and cold weather in particular are conditions most likely to precipitate a severe manifestation.

Thermal movement

Bricks expand on being warmed and shrink when cooled. It is the expansion and contraction of the brickwork as a whole and not a single unit that requires consideration when designing a building.

An increase in the temperature of a wall will induce expansion. The degree of movement is equal to the temperature range multiplied by the appropriate coefficient of thermal movements overcoming restraint in the wall itself – see Table (x) below.

A decrease in temperature will result in the shortening of the wall that may induce cracks. However, the movement that actually occurs within a wall after construction depends not only on the range of temperatures, but also on the initial temperatures of the units as laid, their moisture content and the degree of restraint.

To determine the effective free movement that could occur, therefore, some estimation of the initial temperature and temperature range has to be made. The effective free movement that is calculated should still be modified to allow for the effects of restraints.

Durability

The best indicator of a product’s durability performance in any application is at least five years’ satisfactory performance in the application concerned. A single value of compressive strength alone is not an adequate criterion for a product’s likely durability in an exposed application. For example, the present minimum requirement for facing of 17MPa average compressive strength fails to cater for the requirements of more severe exposure.

Currently, a direct determination of durability does not exist in the form of a proven accelerated weathering test or some other performance-based evaluation, although a programme of research and of measuring the performance of products is ongoing. Durability is the ability of a material to withstand the combined effects of the weathering agents of moisture, soluble salts, frost and thermal changes. Exposure is the severity of these weathering actions, varying from mild to severe, and depending on both regional geographic conditions, and micro-climatic conditions with regard to the building’s height and the material’s position within the building. Parapets and copings, for example, are clearly subject to more severe exposure conditions than face brickwork protected by overhanging eaves. Internal face brickwork is not subject to the same degree of exposure as external, unrendered brickwork.

Zone 1 Protected:
All inland areas more than 30 km from the coastline

Zone 2 Moderate:
The 30 km zone along the coast, but excluding the sea spray zone

Zone 3 Severe:
This consists of the following:

• the sea spray zone such as the seaward sides of Durban Bluff and other exposed coastal headland areas;
• the 15 km coastal zone from Mtunzini northwards to the Mozambique border, including Richards Bay; and
• the coastal belt of Namibia

Types

Common or stock bricks In South Africa we use the term stock brick instead of calling them common bricks. The quality of these bricks varies considerably because they are normally cheaper and are suitable for general-purpose use with no special appearance of a facing.

Masonry units – Clay
NFP – Non-Facing Plastered

Clay bricks suitable for general building work and when used externally require being plastered.

NFX – Non-Facing Extra

Clay bricks suitable for use, plastered or un-plastered; for general building work below damp-proof course or under damp conditions or below ground level where durability rather than aesthetics is the criterion for selection; sometimes referred to as footing or foundation bricks.

Masonry units – Concrete

Concrete common bricks can be used externally without further protection (i.e. plastering) and can be adequately durable and frost resistant.

Face bricks

Face bricks are produced to withstand most environmental conditions as well as provide an aesthetic appearance and do not require and further protection.

Facing and engineering bricks are sometimes pressed after being wire cut to provide smoother faces and sharper arises. Holes formed during the extrusion process vary considerably in number and size. Bricks with a total volume of holes less than 25% of volume of the brick are called perforated bricks.

The advantages of perforated bricks include a reduction in process times, reduction in weight and therefore easier handling on site and some increase in thermal value. The perforations do not appear to affect rain penetration through walls. As the holes go right through the bricks when laid vertically, they are vulnerable to saturation from rain during construction. Saturation may increase drying-out time and increase the probability of what is termed construction water or dampness and may therefore inhibit early decoration, such as painting, due to wet walls.

The difference between a brick and a block is a matter of size, not material and blocks are usually hollow. Concrete blocks are used for both internal and external walls. It is often recommend that they are plastered to provide extra protection against moisture. Blocks are generally used in low-cost housing because they are less expensive than normal stock bricks and speed up construction.

The use of concrete and clay masonry units in the same wall

Concrete and burnt clay masonry units respond differently to temperature, moisture and stress. Consequently when used in the same wall distress may occur. It is therefore not recommended that dissimilar materials be used in the same leaf.

Calculating quantities

The table that follows provides the number of masonry units required per m² of wall for the most commonly used masonry units.

A figure of 10% is usually accepted when making allowance for wastage, which also includes for breakages (during offloading and construction). You would usually require 0.60m³ of mortar per 1000 bricks (standard stock brick) and because of bulking and waste, 1,0m³ of sand would be required for every 0,60m³ of mortar, i.e. 1m³ of sand per 1000 bricks.

Note: The table is based on exact sizes of solid masonry units, with 10 mm thick bedding and vertical joints, and no wastage (Quantities are rounded up).

Thermal insulation

The thermal properties of any walling material are determined by how it handles heat, how heat transfers through it and how well it holds or stores heat. Heat always moves from warm to cold, so in summer with the outside temperature warmer than the inside, the heat transfers into the building through the walls from the outside and vice versa in winter. Masonry is naturally thermally efficient and these thermal properties of masonry units differ from type to type depending upon the materials of manufacture, profile, mass and density; and when used in conjunction with cavity wall construction it has the effect of ensuring that buildings stay warmer in winter and cooler in summer, which can be made even more efficient with the installation of an insulation material in the cavity.

To better understand the thermal properties of walling it is necessary to know the following:

• Thermal transmittance, (U value) is measured in Watts (W) per square metre (m2) per degree Celsius, W/m2 °C as the rate of heat flow through an element e.g. a wall. The lower the U value, the better the insulation properties of the wall: it has a greater resistance to the flow of heat. The U value not only takes into account the resistance offered by the wall, but also the outside and inside surface resistance. Since the U value notionally provides a measure of the heat flow through a wall, it is the figure used to compare the performance of different constructions and to make energy-use calculations.
• Thermal capacity is measured in Joules (J) per square metre (m2) per degree Celsius, J/m2 °C, and is a measure of the degree of heat that can be stored by a wall. Clay brick walls, with their high thermal capacity, have the ability to store heat during the day and release this heat at night (commonly referred to as thermal mass). In climatic regions where there are high temperatures during the day and low temperatures at night, this results in thermally comfortable dwellings with a reduction in energy consumption to cool or heat the buildings.

All the materials of a wall, including any window openings, and even the spaces between layers of the materials (cavities), contribute to its thermal performance. The contribution of the different elements is assessed by testing (more especially for commercial buildings), but for many purposes values are rounded to standardised published values which are used in calculations e.g. for determining heat loads for air-conditioning systems.

Fire resistance

Fire resistance rating is a measure of the length of time a walling element will resist a fully developed fire. Failure occurs in an element when its resistance is overcome in a defined way. Firstly, if it collapses or its structural ability is impaired, it is said to have failed at the time of collapse. Secondly, a wall can fail if it develops cracks and fissures through which hot gas or flame can pass and, thirdly, an element can fail if the temperature on the side away from the fire exceeds a certain level.

The fire resistance rating of masonry walls depends on whether the wall is load-bearing or not, whether solid or hollow masonry units are used and on the geological type of the aggregates used in the manufacture of the units.

Note: Plastering the wall improves the fire resistance rating.

The National Building Regulations requirements for walls are covered in SANS 10400-K. The fire resistance ratings of masonry walls are given in SANS 10145.

Different criteria apply to different building types, heights of walls and the relative position of the wall within the building and to the boundary of the site. Both the resistance to the spread of fire within the building and to adjacent buildings, and the ability of the wall to withstand fire are covered in the supporting documents of the national building regulations. All external walls must be fire-resisting to some degree, which may limit options particularly in respect of openings and their construction, but residential buildings are allowed different limits from other building types.

Retaining walls

Retaining walls are required where there is a difference in levels. The retaining wall is positioned between the two different levels and retains the soil below the higher level. The wall can be constructed of reinforced concrete or brickwork or a combination of the two.

Free-standing retaining walls should be designed and constructed so that:

• the height of fill retained by free-standing retaining walls (see figure 13.16) does not exceed the values given in table 13.14, provided, however, that where x (see figure 13.13) exceeds 0,3 m, the height retained is reduced by the difference between x and 0,3 m,
• piers, where required in terms of table 13.16, project on the opposite side of the wall to the fill that is being retained, • control joints are located at intervals that do not exceed 10 m,
• no surcharge of fill is placed within a distance equal to the height of the amount of fill being retained, and
• Subsoil drainage is provided behind the wall by providing weep-holes formed by building into the wall, 50 mm diameter plastic pipes, with the non-exposed end cut into the perforated pipe installed behind the retaining wall at the bottom of the filling covered with geo-fabric and coarse aggregate, at a height that does not exceed 300 mm above the lower ground level, at centres that do not exceed 1,5 m. Allowing water to pass through the aggregate and geo-fabric, and into the pipes that will exit on the exterior of the wall. The purpose of the agricultural/subsoil drain is to reduce as much water pressure as possible behind the retaining wall.

Brickwork

Damp proof courses

Damp proof courses (DPC) need to be installed to prevent moisture and water seepage through walls etc. DPC is a sheeting of impervious material; Mastic asphalt, bitumen polymer and fibre felt or embossed polyethylene pre-manufactured in rolls, to suit the different widths of brickwork, also available in different thicknesses known as microns (μm) with the most common being 375 μm.

The three basic methods of protection in which DPC courses are used, are:

1. To prevent moisture penetration from below (rising damp)
2. . To prevent moisture penetration from above
3. To prevent moisture penetration from the side (horizontal entry)

Standards

Extracts from SANS 10400: Part K

Any wall or sleeper pier of a building shall be provided with damp proofing and vapour barrier installations in such positions and to an extent that will reliably protect the wall against rising damp and
the interior of the building against ingress of moisture from abutting ground. Any material used as a damp-proof course shall comply with the relevant requirements contained in SANS 248, SANS 298, or SANS 952, or be the subject of an Agrément certificate. In a masonry wall, a damp-proof course shall be installed:

• a) at the level of the top of a concrete floor slab resting \ on the ground; or
• b) Where applicable, below any ground floor timber beam or joist.

Bonds

The reasons for different bonds are firstly structural; bonding is required to strengthen and stabilize and form a monolithic wall, which will enable it to carry vertical and horizontal loads, for example English bond. Then economics (the most cost effective method of laying) and the wastage attributed to different bonds used, especially in blocks.

Note: When Broken Bonding occurs where the length of a brick wall is not equal to brick format sizes, which means that a cut brick must be inserted. The cut brick should not be less than a half brick.

There are two known practical bond methods, that is, the quarter brick lap called the quarter bond, or the half brick lap called the half bond.If the lap is smaller or bigger, both the appearance and the strength of the bond are affected. The term used when no laps occur is the straight joint, which should be avoided in structural walls.

Different bonds

Stretcher bond

This is one of the few bonds, which can be used for half brick walling (single brick). On the face of the wall we see only the long stretcher face of the brick, except at corners, stopped ends and at cross walls. To ensure maximum strength the half bond must be maintained. At the junction of two walls a quarter bond is necessary but by inserting a three-quarter, the half bond is continued.

This consists of alternate courses of headers and stretchers. Because we use a header course this bond is only suitable for walls from one full masonry unit and more i.e. a format of length to width of 2:1. This is a very strong bond because no straight joints appear. It is therefore ideally suited for walls where strength is important like retaining walls.

This method consists of alternate headers and stretchers in the same course. This bond is also reasonably strong because of the header bricks, which tie the two half brick stretcher skins together. This bond is usually used for aesthetics. In order to maintain the bond and avoid straight joints, the header brick in each course must be positioned exactly in the centre of the stretcher brick.

In practice, to maintain proper bonding, the cutting of masonry units to avoid straight joints is unavoidable; however, if the building is designed to standard masonry modules and correctly set out, the cutting of masonry units can be kept to a minimum. See figures 10.30 and 10.31.

Toothing and racking back

Toothing

A full or half brick is removed or a half brick projects from alternative courses of a wall in order to provide adequate bond if the wall is to be joined or connected at a later stage – see figure below. (Toothing is not usually permitted by many local authorities)

The stepped arrangement formed during the construction of a wall when one portion is built to a greater height than an adjoining wall. It is recommended that no part of a wall during its construction should rise more than 900mm above another wall at one lift, if unequal settlement is to be avoided – see figure 13.33.

Jointing and Pointing

The reasons for jointing and pointing are firstly to prevent the penetration of water into the walls and secondly to provide a neat aesthetically pleasing finish, especially when using face bricks. Various tools are used to produce a smooth outer edge to the joints in order to allow water to run off without obstruction and thus prevent it from soaking into the brickwork by means of capillary actio.

Jointing is the process of finishing the face of the joint as the work proceeds. The actual mortar (Dagha) in which the bricks are laid is smoothed by means of the brick trowel or jointing tool; typically done when using stock bricks. Pointing is the process of raking out the joints as the work proceeds and at a later stage, filling and finishing them with specially prepared mortar; typically done on fair-face or face brickwork.

Raked out joints are done with the point of a trowel, a piece of hoop-iron or a nail head projecting from a piece of wood. In some cases raked out joints are left as is – but this is not recommended externally.

Cavity walls

Cavity wall construction should be used in coastal areas, or where exposure conditions are severe, and in high rainfall regions where the external walls do not have a chance to dry out properly. Keeping in mind that single-leaf walls are more vulnerable to moisture penetration than cavity walls in these circumstances.

A cavity wall basically comprises two single brick walls (skins – as it is also known) separated by a cavity of approximately 50mm, where the air space provides an excellent barrier against the passage of moisture. The two skins are tied together using wall ties

. It is very common to find that bricklaying mortar falls into the cavity and collects on wall ties, cavity trays and at the base of the cavity during the building process; resulting in potential bridging of cavities, leading to penetrating damp.

The removal of such mortar droppings from the cavity is critical and can be removed by providing temporary openings at the bottom of the cavity, which can be closed after the bricklaying process is complete and can also be used to form the weepholes.

Narrow cavity widths (less than 50 mm) increase the risk of rain penetration, as do wall ties, which slope downwards towards the inner leaf of the wall, recessed pointing, and inadequate projection of sills, copings, verges or eaves.

NB: Workmanship is particularly important in the construction of the outer skin of a cavity wall, so as to reduce the quantity of water passing into the cavity, and in keeping the cavity clear of obstructions and other faults, which can lead water across. If cavity insulation is to be used, good workmanship is also important for the installation of the insulation, either during construction (for built-in board or batt materials) or after construction (for blown-in or injected fills) – See installing thermal insulation later in this section

Note: In certain areas of the country, the cavity has been replaced effectively by a bitumen layer painted on the outside face of the inner leaf of a double skin wall.

Weepholes

Weepholes should be provided in the external leaf (skin) to prevent the build-up of water or moisture and are usually located in the first course above any damp-proof course membrane, and spaced approximately 900mm apart; and are typically formed as enlarged perpend joints of approximately 20mm wide. In hollow masonry unit walls, the weepholes should be of the same thickness as the bedding course thickness, of approximately 30mm wide and located in the bedding course beneath the hollow masonry unit cores.

Polystyrene boards are the more common choice of cavity wall insulation; cavity fill (loose fill or injected foams) can be used; however, various issues associated with the use of cavity fill insulation have to be considered. Cavity fill is mainly used to insulate existing cavity brick walls. Check that local building regulations allow for the use of cavity fill or ask the manufacturer for a certificate of approval. Cavity fill must be treated to be water repellent. The reduction of heat flow inwards when a cavity wall is insulated using a 30mm polystyrene board compared to uninsulated cavity wall is as high a 64%.

• Brick or block gauges are to be set such that cavity ties occur at 600mm vertical centres to coincide with the
  horizontal joints of the wall insulation.
• Cavity ties must be embedded to a depth of at least 50mm in the mortar joints of each leaf and spaced in the cavity as described above in accordance with SABS 0164, with holding back ties in between, to be embedded as per building standards (see detail A & B figure 13.35, 13,36).
• Boards must be secured against the inner leaf of the wall with the shiplap arranged to shed water away from the inner leaf, or with tongue facing upwards and secured with the holding back ties (see fig 13.3)
• Board support ties to be 2mm galvanised wire with fishtail ends.

Brick reinforcement

Definitions

Reinforced Brickwork – Brickwork incorporating steel wire or rods to enhance its resistance to loads Reinforcing – Metal that is built into brickwork, e.g. reinforcing bars, brickforce.

Brickforce

Brickforce is used to reinforce brickwork especially in foundation brickwork and above the lintels of openings to windows and doors, and should provide a continuous band, particularly in the case of walls less than 190 mm thick, to form a lintel or “ring” beam. It is laid horizontally in the bed joints (the mortar joints) between brick courses and can be placed in every course above lintel height if specified or normally in every third to fourth course or at vertical centres that do not exceed 400mm. Brickforce is a light welded steel fabric made of two hard-drawn wires of diameter not less than 2.8mm and not greater than 3.55mm held apart by either perpendicular (ladder type) or diagonal (truss type) cross wires; perpendicular being the most common.

Where required in terms of the specification data, brickforce should be manufactured from pre-galvanized wire, galvanized in accordance with the requirements of SANS 935 for a grade 2 coating or be made of stainless steel wire.

Rod reinforcement

Reinforcing steel including bed reinforcement shall comply with SANS 920 and SANS 1024. Reinforcement in a bed joint should comprise of hard-drawn pre-straightened deformed steel wire or rod wires that have a proof stress of 485 MPa and a
diameter of not less than 4,0mm and not greater than 6,0mm.

Mild steel has the disadvantage of being difficult to maintain in a straight position and because of its lower yield stress (250 MPa) it is required in larger quantities. At splices in the reinforcement the lap length of 280, 370, 460, 560, and 740mm are required for bar diameters of 6, 8, 10, 12, and 16 mm respectively.

Lintels

Outline

A lintel can be best described as a small beam used over openings, windows, and doors, carrying the wall load only or a superimposed load like a roof. A lintel acts as a permanent shutter allowing bricklaying to continue almost unhindered. However, lintels on their own provide little compressive and tensile strength and only when combined with a number of brick courses, reinforcement and adequate bearing does a lintel then act as a beam, which can carry a load. Precast lintels must meet the following requirements:

• They must contain sufficient steel to carry the load once built in.
• They must be as light, and therefore slender, as possible.
• They must not crack easily when lifted or handled.

It has been found that the last two requirements can be met only if the concrete is pre-stressed, i.e. the concrete is “precompressed” so that it will not crack.

Prestressing is basically done, as follows:

Steel moulds, long enough to make several lintels end to end are placed side by side on a concrete bed. The ends of the moulds have holes in them; the hole diameter is slightly bigger than that of the prestressing wire. Movable stop-end plates, with holes in them, are placed in the moulds to divide the length into individual lintels. After the mould has been treated with release agent to prevent the concrete from sticking to it, the wires are threaded through these holes so that they protrude from each end of the mould. The wires are anchored at one end and connected to a powerful, usually hydraulic, jack at the other end. By activating the jack, the wires are stretched to the required extent and held in this state.

Standards

Guidance on the design of lintels over openings is given in appendix G of the Joint Structural Division of the South African Institution of Civil Engineering and the Institution of Structural Engineers’ Code of practice for foundations and superstructures for single-storey residential buildings of masonry construction. However, The National Building Regulations SANS 10400: Part K provides comprehensive guidelines for the installation of lintels, supporting tiled and sheeted roofs. Lintels which support concrete floors and roofs and timber floors fall outside the scope of this part of SANS 10400 and as such should be designed in accordance with the provisions of SANS 10400-B.

Secondary reinforcement in accordance with table 13.20 shall be provided in the uppermost bed joint. Where the width of piers between openings is less than 750 mm, primary reinforcement in accordance with tables 13.17 to 10.19 as relevant, shall be provided in the uppermost bed joint, in accordance with the requirements of figure 13.37.

Lintels shall be set in mortar and have a minimum bearing of:

Lintel that supports masonry only: 150 mm

Lintel that supports roof trusses

• span less than or equal to 1,5 m: 150 mm
• span between 1,5 m and 2,5 m: 250 mm
• span greater than or equal to 2,5 m: 350 mm

Double garage openings

Lintels over double garage openings, which do not exceed 5,0 m, shall be reinforced in accordance with the provisions of figures 13.41 and 13.42 and table 13.24. Cores and cavities shall be filled with grade 25-infill concrete. Lintels shall be adequately supported for a period of not less than 7 days after completion.

Roof anchoring (ties)

Window sills

A window sill can be best described as the horizontal ledge below a window. An external sill should be weathered outwards (have a fall) and should have a drip underneath to protect the top of the wall against rainwater and to prevent staining (water marks) from occurring on the wall below the sill. In brickwork walls, an external window sill can be of standard imperial bricks laid on edge or special bricks laid on edge, left exposed in the case of face bricks or plastered in the case of plaster (stock) bricks. See figure 13.45 – Typical window sill details on the next page.

Sills manufactured of various other materials like clay or ceramic tiles, precast concrete, fibre cement, and plastics or composites, can be used externally and internally and for obvious reasons timber sills can only be used internally.

Brickwork Movement

Outline

All structures are subjected to varying degrees of dimensional change after construction. Determination of movement in response to the environment is a complex problem and not merely a summation or subtraction of extreme or individual values of thermal and moisture movement, but the response of the masonry to these movements must be considered. It is also, often found that the orientation will induce different movements in various parts of the walls due to the incidence of radiation heat or prevailing rain. That is why one must make allowance for movement joints (which some call expansion, control or soft joints), in the design of buildings. An estimation of potential movement in a masonry element must rely to a great extent on engineering judgment. Many factors, such as temperature and moisture content of masonry units and mortar at the time of construction, the exposure to weather conditions and degree of restraint imposed on elements subject to movement are unpredictable.

In general, it is more simple to adopt empirical rules rather than try to estimate movement in a structure from first principles. Stresses in masonry that are sufficient to cause cracks may be controlled to some extent or reduced by the use of control joints or reinforcement and by the degree of restraint inherent in the masonry and the supporting structure, namely the foundations, beams, slabs, etc. Not all movements are reversible. When the stimulus to movement is removed, for example when severe contractions cause cracks in perpend joints, or when the bond strength between the masonry unit and mortar is exceeded, the crack may not be able to close again due to mechanical interlocking, friction or insufficient force in the opposite direction. With repeated expansion and shrinkage movement, cracks can become filled with debris, resulting in a ratchet effect which results in a continuous increase in length of the masonry. Recommendations for the size and spacing of control joints to accommodate movement are given in SANS 10249 and joint spacing recommendations associated with quantities of reinforcement are given in SANS 10145. Guidelines of spacing between vertical control joint in walls is given in SANS 10400: Part K – see extracts from this standard in standards that follow.

In clay brick walls

Typically, movements can be as much as 5 mm in 7.5 m of wall. Provision is usually taken to be 1 mm per metre to cope with a combination of irreversible moisture expansion, and reversible thermal and moisture movements. The recommendations of SANS 10249 for unreinforced masonry are not concerned exclusively with temperature size changes.

The primary object of control joints is to divide the wall into separate panels in such a way that stresses along its length produced by differential movement and changes in volume of masonry units are relieved.

The design and positioning of control joints should accommodate movements but should not impair the stability of the wall or any of its functions, i.e. impermeability, sound insulation and fire resistance. Vertical control joints should be butt joints and the gap between adjacent surfaces should not exceed 12 mm.

Erecting free-standing columns

Pre-cast concrete columns

• The columns are to stand on properly prepared and designed concrete foundations. The design of the foundation should take into account the size and weight of the column itself, any anticipated external forces, and the nature of the soil conditions. Typically, a freestanding column foundation would have proportions of approx. 400 x 400 x 200 mm.
• Assuming adequate foundations have been prepared, the next step is to drill into the foundation and epoxy in one or more steel rods (diameter approx. 10 mm). These rods are to be positioned so that they correspond with the hole in the centre of the precast base, and should be as near to the sides of the hole so as not to clash with the reinforcing of the shaft. Alternatively, these rods could be positioned at the time of casting the foundation.
• The precast base (if being used) is then positioned over these rods and is bedded down using a strong mortar. Care is to be taken to ensure that the hole in the precast base is not filled. The bases are then left for at least 24 hours, before positioning the column shafts.

Hollow fibre cement building columns

• Building columns are to stand on properly prepared and designed concrete foundations. The design of the foundation should take into account the size and weight of the column including the concrete when filled and any anticipated external forces, and the nature of the soil conditions. Typically, a free-standing column foundation would have proportions of approx. 400 x 400 x 200 mm.
• Assuming adequate foundations have been prepared, the next step is to drill into the foundation and epoxy in one or more steel rods (diameter approx. 10 mm). These rods are to be positioned so that they correspond with the inside diameter of the hollow building column, and should not to clash with the reinforcing of the building column where required. Alternatively, these rods could be positioned at the time of casting the foundation.
• Determine whether any cut-outs in the column are required for services, water outlets, bolts etc. and cut out before the column is placed in position.

Note: Where building columns are designed as load bearing elements in buildings, they should be considered as permanent shuttering only and the reinforced concrete core requires professional expertise and should be designed by a professional engineer.

Bases

Moulded bases are normally used for decorative purposes and to facilitate setting out and are usually manufactured from pre-cast concrete; see example below.

Freestanding walls

Outline

Freestanding walls can be defined as walls not forming part of the building, and are generally used for boundary demarcation, landscaping, screening, security, and noise barriers. By their nature they are exposed to the elements and to wind loadings on both faces and need to be designed to ensure that local wind loadings are taken into consideration. Most freestanding walls are constructed using bricks or blocks and can be finished in either face-brick, semi face, fair face or plastered and painted. Depending upon the height, freestanding walls are usually subject to plan approval by the local authority/municipality.

Walls are normally formed in brickwork, and usually will be reinforced when over 2500mm in height. In sheltered areas, where wind speeds are low, they may be unreinforced up to 3000mm in height, while in areas with high wind speeds lower heights may require reinforcement. As a general rule, walls exceeding a height of 2500mm require that the wall be designed by a structural engineer or other suitably qualified professional.

The minimum requirements of wall thickness and heights are given in the tables below, under standards – Extracts from SANS 10400 Part K. The wall height is measured from the lowest ground level to the top of the wall, capping or coping. For ground slopes of between 1 in 10 and 1 in 20 wall heights should be reduced by 15%. Formal design procedures should be adopted for sites with steeper slopes. Diaphragm wall construction can be used as an alternative to using reinforcement, but is unlikely to be economical. Piers will be needed where gates are to be hung, the design depending on the circumstances.

Foundations

For walls not exceeding 2500mm in height a foundation depth of 500mm is normally adequate in good ground. For higher walls in solid soils the foundation depth should be 750mm minimum. Generally, it should be possible to found a freestanding wall at half the depth recommended for residential buildings (See Foundations). However, where walls are to be founded on highly shrinkable soils (clay) or close to large trees (or where large trees have been removed) foundation depths and details should be based on the recommendations of a structural engineer or that of a suitably qualified professional.

Balustrade and parapet walls shall not be less than 1,0 m inheight unless unauthorized access of persons to the edge of a flat roof or similar structure is excluded by a physical barrier properly erected and monitored. Free-standing balustrade and parapet walls shall have a thickness of not less than the height of the wall above the base divided by:

• a) Solid units:
  1. no DPC at base: 5,0
  2. DPC at base: 4,5.
• b) Hollow units that have cores filled with infill concrete:
  1. no DPC at base: 4,0
  2. DPC at base: 4,0.

Balustrades and parapet walls that have returns which continue for a distance of at least 0,75m from the external face of such walls or are fixed to columns at centres that do not exceed 3,5 m, shall have a thickness of not less than:

• solid units 110 mm
• hollow units 140 mm

A coping is a cover fitted to the tops of freestanding (boundary), parapet and balustrade walls, and to brick piers, also referred to as caps. The primary function of a coping is to prevent moisture from penetrating the tops of walls and also helps reduce streaks being visible on the wall below, because they are usually weathered away at a slope and have drips. Copings advance the long term durability and stability of walls and also provide an aesthetically pleasing finish to walls.

Scaffolding

Scaffolding is a temporary platform carried by a framework erected on site, to give access for trades like (bricklaying, plastering, and painting) and to carry materials. It is usually a modular frame system of metal or aluminium, although it could be made out of other materials.

Scaffold staging or tower scaffolds are usually of steel or aluminium, either of a prefabricated frame type that clip together or of a tubular type joined with fittings, for example a putlog coupler.

Scaffold boards or planks which form the working deck or platform of a scaffold, must be strong enough to carry the materials and workers. They are either wooden planks and should be at least 228mm wide and 50mm thick and not be longer than approximately 4,8m with a maximum support distance of 2,2m; or steel planks which clip into the framework and are typically 228mm wide.

Scaffolds are rarely independent structures. To ensure a constant and workable space between the structure and the scaffold, ties are used to link the two, which also ensures the scaffold remains sturdy.

Scaffolding can be categorised in the following forms
• Steel builders trestles
• Scaffold frames
• Independent (purposely erected) scaffolding
• Mobile scaffolding

Steel builders trestles

A standard steel builders trestle can be used for almost every type of interior and external building activity up to about 2,4m (single storey buildings). It usually accommodates a four board working platform of approx. 1,0m wide, and is easily handled by one person and folds away for quick storage and transport.

Trestles are usually available in the following heights:

• 800 – 1000mm extending to approx. 1.800mm (Ideal for fitting, plastering and painting ceilings)
• 1200 – 1400mm extending to approx. 2.000 – 2400mm (Ideal for brickwork and plastering)

Building up walls

The first thing to do is to lay the damp-proof courses (DPC’s), which must be positioned to cover the full width of the wall including the plaster thickness (if plastering is specified), and should protrude 10 mm from the exterior face of the wall and be turned downwards. The DPC shall be laid with mortar above and below the membrane.

Start at the corners, by firstly positioning the corner profiles and then build up a number courses at each corner, and then lay masonry units between the corners. Keep checking the brick or block gauge and remember to move the gauge line up the corner profiles as the brick or block courses rise.

Where an internal wall is marked, lay one brick or block horizontally along the marking. Then lay the commencing courses with a step at the end of the wall, usually half the horizontal size of the masonry unit being used; the internal wall will then rise in height as the external wall rises in height. This raking back as it is known should not be raised above the level of the external or surrounding brickwork and by not more than 900mm at one lift. Although some of the following factors have been discussed previously, it is important we highlight their importance once again.

Masonry units shall be laid on a bed of mortar in proportions as described under mortars (Dagha) and or as specified on the drawings. All perpend and bed joints shall have a nominal thickness of 10 mm Mortar should not be spread so far ahead of actual laying that it stiffens and loses its plasticity, as this results in poor bonding and weatherproofness.

Note: The consistency of the mortar should be adjusted to suit the degree of suction of the masonry units (IRA) instead of the units being wetted to suit the mortar.

Damp proofing

Damp proof courses shall be installed in accordance with the best practice as described under brickwork and not forgetting the significance of installing vertical damp proof membranes where any changes in floor level occur.

Bonding

Unless otherwise stated or specified, masonry units shall be laid in stretcher bond. Masonry units of dissimilar materials shall not be built into the same wall as described under brick properties and types.

Brick or bed reinforcement

Brickforce or bed reinforcement should be installed in accordance with what was discussed under brickwork – Brick reinforcement and Lintels.

Positioning Windows

When drawing an elevation, one will measure a window from lintel height down. Practically, when building, the wall into which a window is being built will be built from the bottom up. In order to build to an accurate height, measure to lintel height, subtract the specified window height and build up to that point; but remember to leave space for the window sill, which is usually installed after the brickwork has been completed or before the plastering begins.

Once again, when fitting a window frame (for steel or wooden frames), ensure that the frame is at right angles, plumb, and level on top. As with door frames, use a board(s) fixed to the top of the fame and secured with bricks at surface bed level, to keep the frame in place while building the walls up around the frame continues.

See figure 13.66

Note: Windows are generally fitted in the middle of the wall.

Steel window frames come with lugs factory fitted; while in the case of wooden window frames, lugs (usually 150mm wire nails) are fitted on site as building commences, or the wooden frame can be fitted later and then screwed into the wall.

Lintels

Pre-stressed concrete lintels are commonly used in stock brick applications above openings, windows, and doors. While in face brick applications, the brick-on-edge method is often used, where no concrete lintel is fitted, although in some cases a lintel is fitted on the inside skin, above the brick on edge.

We have covered lintels extensively under brickwork mainly because this is one element that is often installed with little consideration of their structural value and long-term safety, leading to widespread and serious long-term consequences.

Arches

The theory of building arches is covered under brickwork; here we only illustrate the basic steps involved in the building of arches.

Note: Mortar for arches should be mixed separately and made stronger (more cement and the addition of a little riversand).

Building in roof anchors

Building in roof anchors to secure roof trusses, rafters, or beams shall be anchored into the wall with a galvanised steel strap or wire to extend into the wall as described under brickwork.

Chasing for services

Horizontal chasing of walls should be avoided where possible. Where chases, holes, and recesses are so made, ensure they do not to impair the strength or stability of the wall. Vertical chases in solid units should not exceed one third of the wall/leaf thickness and horizontal chases should not exceed one sixth of the wall/leaf thickness. Walls constructed of hollow units should not be chased at all and services should be located in the unit cores. Where chasing in these blocks is unavoidable, it should be no deeper than 15mm.