FAQs- Building With Bricks

How much water can a clay brick safely absorb?

The acceptable water absorption rate for face bricks ranges from 4.5% to a maximum of 12%. 

The acceptable water absorption for clay plaster bricks is between 12% and 20%. If you are using engineering bricks the closer you are to the 12% the better the result will be. When the water absorption rate of a plaster bricks is too low, i.e. below 12%, it may be difficult for plaster to obtain a proper adhesion to the plaster brick. 

Handmade historic bricks; many of which are often found to have an average porosity value of around 35%.

With highly porous bricks there is a danger that they might rapidly absorb moisture from the bedding mortar (particularly in warm weather) causing it to stiffen quickly. This would result in it losing the all-important characteristic of plasticity that would inhibit correct and accurate positioning to line and face-plane and the provision of a secure bedding, leading to poor adhesion with attendant negative consequences on aspects of compressive and flexural strengths of the overall walling. 

It is important not to confuse ‘porosity’ with ‘permeability’, as they are not the same. Porosity is a measure of the available pore space within a brick. Permeability, however, is a measure of the extent to which air, water, or other fluid can pass through a brick, and depends on the pore structure and degree to which these pores constitute a means of transporting from the face to the rear of the brick. A brick can be highly porous, yet impermeable, because if its pores are not interconnected then no water falling on its face can pass through them to the back.

What are the basics of laying bricks?

Are you planning a major project? Our user friendly guide “Bricklaying made Easy” is available at Builders Warehouse, or from the CBA for just R150.

Preparation

  • Plan site layout e.g. position of building, material stores, access etc.
  • Store and protect all materials to minimise saturation and contamination.
  • Control the wetting of bricks in hot, windy weather.
  • Do not lay surface saturated bricks.
  • Set out at ground level to locate all openings before commencing bricklaying.
  • Lay out dry and minimise broken bonds.
  • Prepare and take care of gauge rods – they are important quality control equipment.
  • Work all levels from one datum.

Protection of brickwork

The best treatment is to prevent it from getting dirty in the first place – so protect the wall as work progresses from mortar droppings. After the first course of bricks has been laid – protect the base of the wall by laying sand, straw, sawdust or plastic sheeting along the ground. This minimises mud splashes and damage from mortar droppings.

As clay brickwork should be kept dry as possible during construction, cover the walls at the end of each day’s work and during rain in order to keep brickwork free from mortar stains.

At the end of each working day clean the toe boards closest to the wall and turn the boards back to prevent rainfall from splashing mortar and dirt onto the brickwork.

Process & Techniques

  • Mix small batches of mortar to suit building rate and 20 minute initial set timing.
  • Bed all DPC’s on fresh mortar
  • Blend face bricks from a number of packs to minimise colour bonding.
  • Plumb, level and square brickwork
  • Fill all mortar joints solidly to minimise water penetration.
  • Clean mortar dropping from cavities regularly

Any clay face brick or semi-face (fired) brick can be used for a braai. Facebricks are fired to around 1000 – 1250’C to stabilise their structure, and they have a high thermal mass which helps them insulate for heat. The heat in the fireplace would need to be higher than this to have any effect on the brick.

Concrete bricks or any regular concrete product made with Portland cement cannot stand up to high temperatures and will disintegrate at the temperatures required by a pizza oven or braai.

With excessive heat, cement and mortar between the bricks can crumble. Build the outer skin of the sides of the braai/fireplace with a standard mortar mix (1 bag cement : 3 Barrows Sand) with brickforce and cavity ties. Build the inner skin with a well burnt clay face brick (FBX) using a weaker mix (1 bag : 6 Barrows Sand) – this allows more joint movement and reduces cracking from heating.

The base is normally the area that gets the most heat as the fire is resting on this. Here a clay paver or solid clay brick should be laid on a sand bed. Do not cement bed or grout – it must have some movement to allow for heating and cooling expansion / contraction. The bricks / pavers at the opening to the braai can be grouted in to form an edge restraint. The fire generally is never built right at the opening so they don’t get as much heat. Grouting these prevents the pavers behind from falling out / working loose. It acts like a kerbing.

For the sides or a raised bed, you can use an air-set refractory cement (as oppose to a fire-set refractory cement), and minimize the joint space between the bricks – use “buttered joints” i.e. have the bricks very close together.

As with all cleaning procedures a rinsing operation should be carried out shortly after  application, and care taken to dispose of run off solutions safely.

If the above method is not successful with coloured mortars, specialist advice from the coloured mortar supplier should be sought.

On the rare occasions when a vanadium efflorescence is present, hydrochloric acid based cleaners must not come into contact with the efflorescence, otherwise a dark stain will result which will become fixed on the surface.

How is brickforce used in unreinforced walling?

Firstly, what is Brickforce?

Brickforce is a British brand consisting of two main parallel wires joined by in-line welded cross wires. Main wires are manufactured to a flattened profile to simplify location into the mortar joint without steel build-up problems at lap positions corners/junctions or when used in conjunction with wall ties.

There are various other materials that can be used for brick reinforcement, e.g. Mild steel reinforcing rods and expanded metal. These products and others suitable as brick reinforcement are obtainable in rolls of varying lengths and widths, from your local hardware shop or builder supplies merchants.

Why use masonry reinforcement?

Masonry has excellent compessive qualities and the majority of buildings constructed using this material last for many years with little maintenance. However, masonry has no significant tensile strength and movement caused by substrata changes, moisture or thermal effects can cause cracking.

The use of masonry reinforcement is a very simple and cost-effective way of greatly enhancing the strength and durability of masonry construction by providing both structural and crack control benefits.

It ties the wall together thus providing stability. Over unsupported openings like windows ,doors etc., Brickforce strengthens the wall. If you are building on unstable ground (i.e. there is movement in the ground) it is always good practice to use brick force thus ensuring a very stable wall.

Various types of alternative masonry reinforcement products are also available including mesh and wire.

Should new clay bricks be left to dry out before use?

Clay bricks expand fractionally after leaving the kiln (primarily due to moisture in the air) and minute increases in height and width (0.006 percent per annum) continue at a decreasing rate for up to 5 years.Fortunately with clay products the majority of this expansion happens almost immediately the product leaves the kiln and is exposed to atmosphere.

Building walls without control joints that exhibit cracking, appeared to have expanded only 2mm to 4mm;

In the good old days all the bricks would be purchased at the beginning of a project and stored for many months before being used. It was thought this gave them an opportunity to harden and “dry out”.  Today, purchases are JIT (just-in-time) and the timing from order email to delivery to use is less than a week. The age of bricks in stock will vary considerably from factory to factory and region. Obviously if product is in high demand they do not stand too long in the yard before delivery.

There are many sources of movement in walling and paving including ambient moisture levels, temperature, loading and creep, chemical action, ground movement and settlement. For more information, please download the “Movement of Brickwork” technical paper.

Mortar: what materials do I need?

The cost and quality of masonry work is significantly  affected  by the mortar used. Mortars may account for as little as 7% of the volume of the walls, but the role it plays and the influence it has on performance are far greater than the proportion indicates. Mortar provides a bed for laying; bond units together to give compressive and flexural  strength  and seals joints against rain penetration.

Four types of building mortar are detailed in SABS 0164.

COMMON CEMENT

Sand

COMMON CEMENT

Lime: sand

COMMON CEMENT

Sand plus mortar plasticizer

MASONRY CEMENT

Sand (common  = Portland)

Approximate proportions for mortar:

MORTAR CLASS

COMMON CEMENT lt

LIME lt

SAND MEASURED LOOSE & DAMP litres mix

MASONRY CEMENT kg

SAND litres

II

50

0-40

200

50

170

III

50

0-80

300

50

200
  • Class II: Normal load  bearing applications, as   well  as  parapets, balustrades, retaining structures, free-standing and garden walls and other walls potentially exposed to severe damp conditions.
  • Class III: Lightly stressed (e.g. single storey) bearing walls where exposure  to dampness  is  not severe but check NBR and NHBRC.

 

Cementitious Materials

CEM 1 32.5 (ordinary Portland cement) and CEM 11/A (S,V or W) 32.5 (Portland cement 15) may be used in mortar.

It is not advisable to use CEM 111/A 32.5 (PBFC), unless the mortar sands are good quality.  Mortar  with common cement lacks plasticity, may bleed, and will be harsh to work with. This deficiency may be overcome by using masonry cement. The use of lime in the mortar mix is beneficial  but is difficult to obtain. Masonry cements are readily available.

When sealed in airtight drums, cement remains the same in strength for up to 3 years. When packed in sacks, even under good conditions, deterioration in the strength of the cement will occur, with a prolonged shelf life, for example: 20% loss after 3 months, a 30% loss after 6 months and a 40% loss after 1 year. The arrangements for storing or stocking cement should be such that batches are used in the same order in which they were received. First in – first out.

Sand

Sand for mortar should comply with SABS 1090 and be well graded from 5mm downwards.  Sand should be evenly graded and should not contain an excess of dust or other fine material. The use of fine sands, that are more or less uniform in particle size, may contribute  to workability, but frequently leads to excessive shrinkage and cracking of the joints. Sands containing high percentage of clay, tend to give a conveniently plastic mix, but also leads to undue shrinkage.

Lime

Lime used in mortar is hydrated lime (commercial bedding lime) and not quicklime or agricultural lime. Lime give the best results when used with coarse sands. Lime with clayey sands can make the mortar over-cohesive and difficult to use. Lime should not be used with masonry cement.

The use of limes added to cement mortars is recommended as the improved workability and water retentively will lead to superior brick to mortar adhesion, with improved resistance of the brickwork to rain penetration.

Mortar: what are my mixing quantities?

Mortar must not be used after it has started to set, which usually occurs about two hours after it has been mixed. One man – particularly if he is a weekend builder – can probably lay a little more than 60 bricks an hour. If you are working on your own or with one assistant, it is better to mix a number of small batches as they are required than to mix a one-bag batch. Do not use too thick a layer of mortar between bricks or blocks; this is wasteful and may lead to cracking.

Mortar class

  • Class I:  Highly stressed masonry incorporating high-strength structural units such as might be used in multi-storey load-bearing buildings; reinforced masonry.
  • Class II: Normal loadbearing applications, as well as parapets, balustrades, retaining structures, and freestanding and garden walls, and other walls exposed to possible severe dampness. In practice, Class II mortars are used for most applications.

The amount of water added to a mix must be enough to make the mix workable and plastic

Masonry cement must comply with SANS 50413-1: Strength class 22,5X. The addition of lime to masonry cements is not permitted

MORTAR:

  • For laying bricks and blocks in normal applications (SABS Class II)
  • To lay 1000 bricks = 3 bags cement + 0.6 cu. m. sand
  • 1 Bag of cement to 3 wheelbarrows of building sand

PLASTER:

  • For exterior and interior work
  • To lay 100sq.m. (15mm thick) = 10 bags cement + 2 cu. m. sand
  • 1 Bag of cement to 3 wheelbarrows of plaster sand

What bonds or jointing should I use?

Bonding brickwork means the arrangement in brickwork so that the units are tied together to form a solid mass. The load is then evenly distributed along the length of the wall.
These drawings show what happens to a wall that is not bonded and one that is bonded.

There are two methods of lapping:

  • The half brick lap
  • The quarter-brick lap, also known as the half bond and the quarter bond.

If bricks are so placed that no lap occurs, the cross joints or perpends are directly over each other, and we have what is known as ‘straight joints’, which must be avoided at all costs.

There are basically three types of bonds used in South African construction and examples of all three can be seen in all towns and cities, – the Stretcher Bond, English Bond and Flemish bond.

Stretcher bond
(alternate layers of stretchers)

Consists of bricks laid lengthways along the line and mapped. This is by far the most commonly used bond in South Africa. In cavity wall construction this is the most economical bond to employ.

English bond
Consists of alternate courses of headers and stretchers. This bond is believed to be the strongest bond because of the header across bonding. It is usually employed in foundation walling behind the half-brick outer skin, and for retaining walls

Flemish bond
Consists of headers and stretchers in the same course.

Mortar class

  • Class I:  Highly stressed masonry incorporating high-strength structural units such as might be used in multi-storey load-bearing buildings; reinforced masonry.
  • Class II: Normal loadbearing applications, as well as parapets, balustrades, retaining structures, and freestanding and garden walls, and other walls exposed to possible severe dampness. In practice, Class II mortars are used for most applications.

The amount of water added to a mix must be enough to make the mix workable and plastic

Masonry cement must comply with SANS 50413-1: Strength class 22,5X. The addition of lime to masonry cements is not permitted

MORTAR:

  • For laying bricks and blocks in normal applications (SABS Class II)
  • To lay 1000 bricks = 3 bags cement + 0.6 cu. m. sand
  • 1 Bag of cement to 3 wheelbarrows of building sand

PLASTER:

  • For exterior and interior work
  • To lay 100sq.m. (15mm thick) = 10 bags cement + 2 cu. m. sand
  • 1 Bag of cement to 3 wheelbarrows of plaster sand

What should I know about buying bricks?

When ordering or specifying clay bricks, ensure the following points are discussed and made known to the suppliers:

  • Expected sizes. Not all bricks are manufactured to the standard imperial size of 222mm long x 106mm wide x 73mm high
  • The required application e.g. type of building, finish etc.
  • The degree of exposure to weather conditions, closeness to the seas etc.
  • The track record of the preferred brick in the area where you are building
  • An undertaking or warranty from the brick supplier that the bricks delivered will be fit for purpose
  • Colour expectations in the case of face bricks or exposed brick areas
  • The acceptable levels of breakage during delivery to site
  • The the brick manufacturer registered with the Clay Brick Association of SA.

To avoid colour banding it is highly recommended that face bricks are taken from a number of different packs and carefully blended during building operations.

 Properties that require consideration when buying or specifying clay brick are:

  • Compressive strength (varies from 7MPa to 50MPa)
  • Water absorption (face brick up to 10%, NFP up to 16%)
  • Modulus of rupture – strength in bending
  • Moisture expansion – important when detailing long walls
  • Initial rate of absorption: This affects the development of bond between the mortar and the brick. Bricks with high rates of absorption (often lower quality) may require pre-wetting well before laying to prevent absorbing excessive water from the mortar mix. Trial and error experiments when bricks arrive on site will determine the need to pre-wet bricks.

Moss, lichens and algae should not grow on clay bricks unless the area is heavily shaded, is under trees, or is not laid to an adequate fall. If such growth does occur and is considered undesirable then the area should be treated with a proprietary moss killer used in accordance with the manufacturer’s instructions.Such products take some days to be effective and work best when applied during a spell of dry weather. Any thick growths should be scraped off first and the chemical treatment well brushed in.

Some treatments leave a residue to discourage the re-growth of the moss and algae, but this will only be of limited value if the paving remains damp and in shade.

Non-chemical control

  • Dislodge moss from between paving by running a sharp knife along the cracks. Alternatively, use a block paving brush with a long handle, narrow head and wire bristles for effective cleaning without stooping
  • A pressure washer will remove moss and algae effectively.  However, use this method with care in areas where drainage is unsatisfactory as the extra water could exacerbate damp problems. Always wear goggles when using a pressure washer.
  • Brush hard surfaces with a stiff broom on a regular basis to help prevent growths from taking hold. Raking loose surfaces such as gravel helps to keep these areas free of both moss and weeds
  • Prune overhanging plants to improve air flow – this will allow the drying effects of sun and wind to reach the site
  • Ensure surfaces slope slightly to prevent standing water
  • Improving drainage in the surrounding area will also help to deter growths. Dig out shallow channels along the edges of paths, patios and drives and fill with coarse gravel to absorb run off water
  • Fork over beds close to damp surfaces to maximise drainage and water absorption
  • Only pave areas essential for access. Choose permeable paving when constructing new hard surfaces and keep drains clear of leaves and debris
  • Surface finishes that are raised to give grip in wet weather are ideal for shady spots. Spreading coarse sand over garden steps is another simple anti-slip solution

What are the standard sizes of clay bricks?

The standard imperial size is 222mm long x 106mm wide x 73mm high with a mass of between 3.0kg and 3.5kg.

Two important criteria determine this size. First, it is the ideal width for the human hand to lift and place in position with minimum strain and secondly, it satisfies the need for bricks to be modular in terms of BOND patterns. Thus there is an approximate arithmetic relationship of length to width of 2:1 and in length to height of 3:1, which allows for bonding in any direction.

However every manufacturer can offer and range of sizes and dimensions to suit different applications.

Common brick sizes

LENGTH (mm)

222

222

222

222

222

190

190

290

290

390

WIDTH (mm)

90

40

90

140

110

90

106

90

150

190

HEIGHT (mm)

73

73

114

114

73

90

90

90

190

90

Superbricks & Maxis

“Superbricks” come in a range of non-standard, large sizes that lower material costs, use less mortar and have fewer joins per square metre. With 140mm wide bricks, one can build a single leaf wall that meets SABS10400XA for a single leaf wall.

For winter rainfall coastal regions, manufacturers have developed brick formats that are narrower and taller than the imperial brick to reduce labour and costs of double skin cavity wall construction.

Fewer bricks per m² afford savings in mortar and accelerate the speed of construction consequent to fewer bricks per m² laid. But as this is still a double leaf wall, the property owner still enjoys all the benefits of double leaf cavity clay brick walling

Special Shapes

A range of special shapes are available to enhance the aesthetic detailing of buildings and landscaped areas. The most common specials available are the cants and the bullnose bricks although special shapes can also be manufactured to specification. It is advisable to discuss your requirements with your supplier.

What is the white, powdery substance on my bricks?

Efflorescence is a powdery deposit of salts which forms on the surface of bricks and paving. It is usually white but efflorescence can be yellow, green or brown.

Efflorescence does not in any way influence the structural strength of clay bricks or pavers. Roman buildings that have been standing for 2 000 years can show efflorescence

A temporary efflorescence is particularly common on new brickwork and paving as soluble salts are dissolved and transported to the surface of the brickwork and paving by water. The efflorescence on new well fired brickwork and paving may be unsightly, but it will not cause damage unless the brickwork and paving are under-fired or soft-fired, in which case serious efflorescence can cause flaking of the surface of the brick or paver.

Efflorescence can occur from a variety of sources. Besides the brickwork, soluble salts can originate from the sand, mortar and the water used. Ground waters that are naturally salt-bearing can be drawn into the base of the brickwork and paving.

Remedies

The best removal method is simply to brush off the deposit with a stiff dry bristle brush after the wall has dried out. Collect the removed salts with a dust pan or a vacuum cleaner to prevent the salts re-entering the brickwork. Wetting the wall by methods such as hosing usually dissolves efflorescence back into the brickwork, allowing it to reappear again when the wall dries out.

Acid or alkaline treatments are not recommended as they do more harm than good because they add to the total salt content.

High pressure washers can remove the surface of the brick, resulting in serious deterioration in the long term.

Dries V of Cermalab

What brick do I use to build a fire wall?

Question continues: “The walls are 3m high by 4.5m wide by 0.2m thick, and supported at each end of the 4.5m  I believe this will have a fire rating of 240 minutes?  How do I support the wall for strength against wind? Are steel wire wall ties sufficient? “

ANSWER

You do not need a special type of brick such as a fire brick. I suggest a double skin masonry wall in standard imperial clay brick, with each leaf 106 mm in thickness. This will yield an overall wall thickness (unplastered) of 212 mm which will have a nominal fire rating of 240 minutes.

I would recommend supporting each 4 meter length of wall with a 340 x340mm brick pillar at each end, as well as using wire ties (brickforce) as suggested.

Chris Dickinson
Corobrik