Frequently Asked Questions

The acceptable water absorption for clay bricks are 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 is too low, i.e. below 12%, it may be difficult to obtain a proper bond between the mortar and the bricks.

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...

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It is common to find growths such as algae, lichens, liverworts and moss growing on hard surfaces. Contrary to popular belief, they do not damage what they are growing on, but can cause patios, drives, paths and steps to become slippery.

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...
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Firebricks (or refractory bricks) are totally over-specification in a domestic fireplace or braai. They are also expensive and not easily available. Refractory Bricks are normally rated from around 1600’C upwards - a braai will never reach this heat.

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...

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Full Question

Referring to SANS 1575 Burnt clay paving units Modulus of rupture 7.6.11

c) a mechanism capable of applying a force uniformly along the cylinder and of increasing the stress at a rate of 1MPa +- 0.2MPa per second.

What would be the load rate in Newton's per second for a sample 200mm long x 100mm wide x 50mm thick?

Answer

1 pascal = 1[N/m²] therefore  1Mpa = 1 000 000  [N/m²] or for ease of calculation 1 MPa = 1000[kN/m²]

Martin Hughes
Corobrik

Oil stains

Oil does not penetrate readily into clay pavers, but if oil is spilt on the pavers, the spillage should be removed promptly with an absorbent material, such as paper towels. The oil should not be wiped up; otherwise this will spread the contamination on the surface of the paver.

Steam cleaning can be used on clay pavers to remove such staining, but if this is unsuccessful an emulsifying de-greaser should be employed. Brush with plenty of water to safe disposal. An alternative cleaning method is to brush the area with a strong detergent and hot water. This will not affect the colour of the clay paving.

Bitumen stains

Bitumen does not penetrate readily into clay paving. The best method of removal is to leave the bitumen until it has cooled. A paint scraper or a similar mechanical device can then often remove it. If it is particularly resistant, the use of ice to make the bitumen even more brittle may be required, prior to scraping it from the paving.

Any residue should be removed with a scouring powder and finally the whole area rinsed with clean water. Certain proprietary cleaning agents are available to remove bitumen, but these...

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Please refer to our Technical guides under `SALT ZONES` and salt erosion of clay bricks.

If you have a property situated on the beachfront there is usually some degree of deterioration taking place! All bricks are porous and will absorb salt, and many factors are at play so it is impossible to say how long it will be before deterioration of the façade begins. The softer lime mortar used in external brickwork prior to the 1960's can be substantially affected by salt deterioration. This is more prevalent in the exposed location but  buildings located 2-3 kilometres from the sea can also be affected. The mortar becomes soft and powdery.

More recent Calcium Silicate face bricks can still suffer from surface delamination. This occurs as the salt crystals adhere to the brickwork and are absorbed into the bricks. During rain the crystals will expand and then push the outer surface of the brickwork away. Once the hardened surface of the brickwork is lost, then the rate of deterioration of brickwork will accelerate. It is not possible to prevent the surface delamination of bricks. 

We have however noticed that the higher temperatured bricks like steel blues are...

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Remove large deposits with wooden implements to avoid damaging the paver surface. Following the pre-wetting of the area, treat the residue of mortar by careful application of a dilute hydrochloric acid solution or a proprietary cleaning solution. The application of the acid breaks down the cementitious components but is not damaging to clay pavers.

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.

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...

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A burnt clay facebrick type product is resistant to petrol and diesel. For many years Caltex specified only clay pavers for their garage forecourts for this reason (Tarmac was never used as petrol and diesel attack it) Although petrol can stain bricks, they are easy to clean.

Acid resistant clay tanks are common in industry and these willl also cope best with petrol and diesel. We would suggest a specialized mortar and possibly a lining is used. There are many specialist suppliers – just search the net!

The acid and chemical resistant clay bricks are featured products in various construction and refractory applications and are available in various shapes and types such as Arch Bricks, Tapper Bricks, Sleeves, Tongue & Groove Bricks.

Chemical resistant clay bricks are used in following application areas:

  • Chemical plants: Dyes, Intermediates, Acids and Alkalies
  • Fertilizer Plants
  • Thermal power plants for chimney construction
  • Petrochemicals and refineries
  • Pharmaceuticals etc
  • Galvanizing Plants

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...

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Brick is porous, so paint sinks into all the grooves on the surface. It is impossible to scrape like wood, and interior walls cannot easily be water- or sand-blasted. Chemical and gel masonry strippers are the solution for inside walls; and while the process of stripping the brick is not complicated, it involves multiple applications of stripper and lots of scrubbing, making it a time-consuming project.

Fresh wet paint should be soaked up with an absorbent material without wiping the paint, as this will spread the stain. It should then be treated with a suitable solvent, such as white spirit, and then the area washed with a de-greasing agent taking care in the disposal of the run-off material.

With dried paint, the paint should be scraped off as far as possible and then a paint remover to BS3761 (4) should be applied.

  1. Put on safety goggles, a face mask and work gloves to avoid coming into contact with the stripper chemicals or fumes.
  2. Brush the masonry paint stripper generously over the brick wall with the brush, starting with one corner and working outward and downward. Reposition the ladder to work on the top of the wall first all the way...
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To avoid confusion and to standardize, the following terminology was introduced and is currently used by the industry.

FBS - FACE BRICK STANDARD
Clay bricks that are selected or produced for their durability and uniformity of size and shape.

NFP - NON-FACING PLASTERED
Clay bricks suitable for general building work that is to be plastered

FBX - FACE BRICK EXTRA
Clay bricks that are selected or produced for their durability and high degree of uniformity of size, shape and colour

NFX - NON-FACING EXTRA
Clay bricks suitable for use, plastered or unplastered, for general building work where durability rather than aesthetics is the key selection criteria: below damp-proof course or under damp conditions or below ground level

FBA - FACE BRICK AESTHETIC
Clay bricks that are selected or produced for their durability and aesthetic effect deriving from non-uniformity of size, shape or colour.

...E - ENGINEERING UNITS
Masonry units produced for structural or load-bearing purposes in face or non-face work, where the manufacturer suppliers clay bricks to an agreed compressive strength. An engineering unit is...

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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 "...

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A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency. Usually dense firebricks are used in applications with extreme mechanical, chemical, or thermal stresses, such as the inside of a kiln or a furnace, which is subject to abrasion from wood, fluxing from ash or slag, and high temperatures.

In the making of firebrick, fireclay is fired in the kiln until it is partly vitrified, and for special purposes may also be glazed.

High-grade fire clays can withstand temperatures of 1775 °C (3227 °F), but to be referred to as a "fire clay" the material must withstand a minimum temperature of 1,515 °C (2,759 °F). Therefore Fire bricks are not needed in braai or fireplaces - a good quality FBX brick will be more than sufficient for the bed of the fireplace, while a standard FBA or NFP brick is sufficient for the sides.

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%,...
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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

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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...

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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:

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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...

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Well-made clay bricks should never require wetting before laying except (rarely) under extremely hot and windy conditions.

Pressed or extruded bricks of low porosity should never be wetted prior to bricklaying as they naturally have a significantly reduced water uptake (and almost zero with a Class A engineering brick) that, if wetted, would result in the brick retaining a thin film of water on all its surfaces and this would cause it to ‘swim’ on the bedding mortar; and that invariably leads to it both sliding out of face line and sinking out of level. If this happens adjust the water content of the mortar so that it is used as stiff as possible.

Clay bricks purchased from non-accredited sources could have unacceptably high porosity and water absorption rates and might need to be soaked on site with water before being used.

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...

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economical

Economical & Practical

energy savings

Energy Efficient & Sustainable

value

Desirable & Stylish