Selecting bricks

How many types of clay brick are there?

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 designated by the addition of the letter E followed by a number equal to the nominal compressive strength in megapascals eg FBSE21.

PA – CLAY PAVERS (1:1, 2:1 OR 3:1)
Clay pavers that are selected or produced for their durability and for a high degree of uniformity in size and shape, and that have dimensions such that the ratio of work size length to work size is approximately 1:1, 2:1 or 3:1.

PB – CLAY PAVERS
Clay pavers that are selected or produced for their durability and for their uniformity in size and shape.

Do I need Fire bricks for a fireplace or braai?

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 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 do I calculate load rate for SANS 1575?

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

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

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