Selecting 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.

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.