Clay Brick and Facing Brick

Solid pressed brick, typically 55 x 105 x 220 mm, remains the standard masonry unit and serves partition and perimeter walls in framed buildings. Perforated clay units of 200 x 200 x 100 or 200 x 200 x 150 mm are lighter and speed up construction, though their compressive strength is lower. Facing brick is produced in thinner formats and in yellow, red and buff tones, and should be selected for frost durability and resistance to efflorescence rather than colour alone.

Firing quality can be judged by sound: a well-fired brick rings clearly, while an underfired one sounds dull. Underfired brick is lighter in colour, absorbs more water and spalls under rain and frost. Suitable absorption for masonry brick generally falls between 8 and 20 per cent by weight. Higher values mean a thirsty brick that dries the mortar; much lower values mean weak mortar bond.

The most common site error is laying dry brick. A thirsty unit pulls water out of the mortar, the cement cannot hydrate and the joint turns powdery and weak. Brick should be dampened before laying, but not soaked. The second error is leaving perpend joints unfilled, which cuts both shear strength and acoustic performance. The third, specific to brick facades, is pointing with an over-rich cement mortar, which produces cracking and white efflorescence.

Efflorescence, the white bloom on brickwork, comes from soluble salts in the brick or mortar carried to the surface by moisture. It is controlled by choosing low-salt brick, waterproofing the wall head and preventing moisture entering from behind the facade, not by repeatedly washing the surface.