Rendering Calculator — Sand, Cement & Render Materials

The standard mix for external rendering in the UK is 1:5 (1 part cement to 5 parts sharp sand) for a general-purpose render. A stronger 1:4 mix is used for the scratch coat or in exposed locations. Always use sharp sand (not building sand) and add plasticiser to improve workability.

Traditional sand and cement rendering typically requires 2 coats: a scratch coat (8-10mm) and a top coat (6-8mm), giving a total thickness of around 15-20mm. Monocouche (one-coat) render is applied in a single 20-25mm coat. Silicone and acrylic renders are usually applied in 1-2 thin coats (1.5-2mm each) over a base coat system.

It depends on the coat thickness. For a typical sand and cement render with a 10mm scratch coat + 7mm float coat (17mm total), you need approximately 27 kg of sharp sand per m² (1 m² × 0.017 m × 1600 kg/m³). So 1 tonne of sharp sand covers roughly 37 m² for a typical 2-coat job. That's about 63 m² at 10mm scratch alone (1000 kg ÷ 16 kg/m²) and 89 m² at 7mm float alone (1000 kg ÷ 11.2 kg/m²). Set each coat's thickness in the calculator independently: scratch coats are usually 10-12mm and float coats 6-8mm.

For traditional sand and cement: scratch coat 8-12mm (10mm typical, slightly stronger 1:4 mix for keying), float (top) coat 6-8mm (7mm typical, 1:5 mix), giving 14-20mm total. Single thick coats are 12-15mm. Heavy renders for uneven substrates can go up to 25mm total over 2-3 coats. Monocouche is applied in one 18-22mm coat. Silicone and acrylic thin-coat renders are 1.5-3mm depending on the product: TC15 is 1.5mm, TC30 is 3mm. Heritage lime renders are 8-12mm per coat over 2-3 coats. The calculator now takes a separate thickness for each coat so you can mix scratch + float thicknesses accurately.

That's correct and intentional: the sand quantity for a given mortar volume is independent of the cement:sand ratio. This is the standard yield method used across UK construction (per BRE Digest 362, NHBC Standards 6.11.6 (Render: Mixes), BS EN 998-1 and Hanson Cement's published rates). When you mix cement and sand together with water, the cement particles fill the voids between the sand grains rather than adding extra volume to the finished mortar. So 1 m³ of finished mortar always needs roughly 1.6 tonnes of sharp sand (or 1.5 t of building sand) regardless of whether you mix at 1:4, 1:5 or 1:6. What changes is the cement bag count. Stronger mix (1:4) needs more cement (~14 bags/m³); standard (1:5) needs less (~12 bags/m³); weaker sheltered (1:6) needs even less (~10 bags/m³).

Monocouche (meaning 'one coat' in French) is a factory-made render that combines cement, aggregates, and additives. It is applied in a single 20-25mm coat, saving time compared to traditional 2-coat rendering. Popular UK brands include Weber, K Rend, and Parex. It comes pre-coloured, so no painting is needed. Use our Monocouche Render Calculator for quantities, or our K Rend Render Calculator for K Rend specifically.

Sand and cement render should be kept damp for the first 2-3 days to prevent cracking, then allowed to dry for at least 7 days before the next coat. Monocouche render typically needs 24-48 hours before it can be finished. Full curing takes 28 days for cement-based renders. Do not render in freezing conditions. For internal plaster drying, see our Plaster Drying Time Estimator.