Brick & Plaster Calculators

For a standard modular brick (190 × 90 × 90 mm with 10 mm mortar joints), a 4.5-inch (half-brick) wall requires about 5.6 bricks per square foot, and a 9-inch (full-brick) wall requires about 11.2 bricks per square foot. These numbers include mortar joints but not breakage — add 3–5 % for handling and cutting waste. Non-modular or regional brick sizes will differ, so always measure the actual brick dimensions on your site.

For load-bearing walls, a 1:4 or 1:5 cement-to-sand ratio is standard. For non-load-bearing partition walls, 1:6 is common and more economical. In heritage or lime-mortar construction, ratios like 1:1:6 (cement : lime : sand) give better workability and flexibility. The mortar should be used within 30–45 minutes of mixing to maintain bond strength — do not re-temper mortar that has started to set.

Internal walls typically receive 12 mm of plaster in a single coat, while external walls get 18–20 mm applied in two coats (a 12 mm base coat and a 6–8 mm finishing coat). Ceilings usually get a thinner 6–8 mm coat because excess thickness risks sagging. If the wall surface is very uneven, a thicker scratch coat may be needed first, but avoid exceeding 25 mm in a single application to prevent cracking.

A 9-inch wall (one full brick length) is used for external walls and load-bearing walls that carry slab and beam loads. A 4.5-inch wall (half-brick) is used for internal partition walls that only support their own weight. Building codes in most regions require external walls of habitable rooms to be at least 9 inches thick for structural stability and weather resistance. Using 4.5-inch walls where 9-inch is required is a serious structural risk — always follow the approved drawings.