Plaster Calculator — South Africa
Calculate cement bags and plaster sand for any SA wall. Covers scratch and finish coats with standard 1:4 and 1:6 mix ratios.
⚠️ For planning purposes only. Allow new plaster a minimum of 28 days before painting.
Plastering in South Africa — The Complete Guide
Plastering is the process of applying a cement-sand mortar to masonry walls to create a smooth, even surface ready for painting or tiling. In South Africa, the standard approach is a two-coat plaster system — a scratch coat (render) for evenness and bonding, followed by a finish coat for the final smooth surface. Understanding the materials required before starting ensures you can order correctly and avoid project delays.
SA Standard Plaster Mix Ratios
| Coat | Thickness | Mix Ratio | Cement / 10m² | Sand / 10m² |
|---|---|---|---|---|
| Scratch coat | 12mm | 1:4 cement:plaster sand | ~1.4 bags (50kg) | ~0.07 m³ |
| Finish coat | 6mm | 1:6 cement:plaster sand | ~0.4 bags (50kg) | ~0.04 m³ |
| Total (two-coat) | 18mm | Combined | ~1.8 bags | ~0.11 m³ |
| Single coat (exposed) | 15mm | 1:3 cement:sand | ~1.8 bags | ~0.07 m³ |
Plaster Calculator Formula
Net wall area (m²) = (Length × Height) − Openings
Volume per coat (m³) = Net area × Coat thickness (m)
Cement bags = Volume ÷ (ratio + 1) ÷ 0.033 m³/bag
Sand (m³) = Volume × ratio ÷ (ratio + 1)
All quantities × wastage factor (1.10 standard)
Plaster Sand vs Building Sand — The Critical Difference
Always use plaster sand for plastering in South Africa — not coarse building sand (used for mortar and concrete). Plaster sand has a finer grading (typically passing a 2mm sieve) that produces a workable, smooth mix. Coarse building sand is too angular and produces a rough, unworkable plaster that is difficult to trowel smooth. In some SA regions, plaster sand is sold as "pit sand" or "fine sand" — confirm with your supplier that it is suitable for plastering before ordering.
Bonding Agents and Surface Preparation
On very smooth concrete or low-absorption masonry, a bonding agent (such as Cemplus, Sika Bond or a PVA-cement slurry) should be applied before plastering to improve adhesion. On normal fired brick or block masonry, wetting the surface thoroughly before applying the scratch coat is sufficient. Do not plaster onto surfaces with active damp, contamination (oil, paint, efflorescence) or loose material — these must be remedied first or the plaster will delaminate.