How Much Sand and Cement to Render a Wall? Bags and Tonnes (UK)
Rendering a wall of 20 m² at 20 mm thick with a 4 : 1 mix takes 7 bags of 25 kg cement and 0.8 tonnes of building sand, with 15% waste. That is about 8.6 kg of cement for every square metre. The render calculator works it out for your own wall, thickness and mix.
Sand and cement for common walls
With a 4 : 1 mix and 15% waste, for no openings, at two thicknesses:
| Wall | Area | Render at 20 mm | Materials at 20 mm | Materials at 15 mm |
|---|---|---|---|---|
| 4 × 2.4 m | 9.6 m² | 0.22 m³ | 4 bags and 0.37 t sand | 3 bags and 0.28 t sand |
| 6 × 2.4 m | 14.4 m² | 0.33 m³ | 5 bags and 0.55 t sand | 4 bags and 0.41 t sand |
| 8 × 3 m | 24.0 m² | 0.55 m³ | 9 bags and 0.92 t sand | 7 bags and 0.69 t sand |
| 10 × 3 m | 30.0 m² | 0.69 m³ | 11 bags and 1.15 t sand | 8 bags and 0.86 t sand |
| 12 × 5 m | 60.0 m² | 1.38 m³ | 21 bags and 2.30 t sand | 16 bags and 1.72 t sand |
| 15 × 6 m | 90.0 m² | 2.07 m³ | 32 bags and 3.44 t sand | 24 bags and 2.58 t sand |
How thickness changes the amount
For a wall of 20 m² (8 × 3 m less 4 m² of openings) at 4 : 1:
| Thickness | Render | Cement bags | Building sand | Cement per m² |
|---|---|---|---|---|
| 10 mm | 0.23 m³ | 4 | 0.38 t | 4.3 kg |
| 15 mm | 0.35 m³ | 6 | 0.57 t | 6.5 kg |
| 20 mm | 0.46 m³ | 7 | 0.77 t | 8.6 kg |
| 25 mm | 0.58 m³ | 9 | 0.96 t | 10.8 kg |
Which mix?
The amount of cement for the same wall, by mix:
| Mix (sand : cement) | Use | Cement | Building sand |
|---|---|---|---|
| 3 : 1 | A rich mix for a base coat on an exposed wall | 9 bags (215 kg) | 0.72 t |
| 4 : 1 | General purpose, and the usual base coat | 7 bags (172 kg) | 0.77 t |
| 5 : 1 | A finishing coat | 6 bags (144 kg) | 0.80 t |
| 6 : 1 | A sheltered or internal wall | 5 bags (123 kg) | 0.82 t |
A richer mix is stronger and less porous, but shrinks and cracks more and can pull the face off a weak wall. Match the render to the wall: a strong mix on old soft brick or stone is a mistake.
How to render a wall
- Prepare the wall. Remove loose paint, dust and crumbling material, repair holes, and fix beads at the corners and the base. Dampen a dry wall.
- Mix the render in small batches by volume: use a bucket as one part. Mix the dry sand and cement first, then add water and plasticiser until it is a stiff, buttery mix.
- Apply the base coat about 10 to 12 mm thick, level it with a straight edge, and score the surface for the next coat.
- Let it firm up for a day or so, and keep it damp.
- Apply the finishing coat about 6 to 8 mm thick with a leaner mix, and finish it with a float or a sponge, or leave it textured.
- Cure it: keep it damp for several days and protect it from frost, strong sun and rain.
Before you start
- Check the weather. Do not render in frost, hot sun or rain.
- On a damp or very old wall, ask a builder: the damp must be dealt with first.
- Buy the sand and cement together, with a little extra: the bags are cheap and a short supply is a nuisance.
- Use a render that is made for the wall. For very rough or painted walls, a sand and cement render needs a bonding coat.
See the sand and cement mix ratios guide for concrete, screed and mortar, and the brick calculator for the mortar for a wall. Estimates only: confirm quantities with your supplier.
Frequently asked questions
How much sand and cement do I need to render a wall?
For 20 m² at 20 mm thick with a 4 : 1 mix and 15% waste, about 7 bags of 25 kg cement and 0.8 tonnes of building sand: about 8.6 kg of cement for each square metre of wall.
How many bags of cement to render 10 square metres?
About 4 bags at 20 mm thick and 4 : 1, with 15% waste, and 0.38 tonnes of building sand.
What is the best sand and cement mix for rendering?
A 4 : 1 mix of building sand to cement is a good general-purpose choice. Use 3 : 1 for a strong base coat on an exposed wall and 5 : 1 or 6 : 1 for the finishing coat. It should be no stronger than the wall.
How thick should render be?
About 15 to 20 mm in total on most walls, put on in two coats: a base coat of 10 to 12 mm, then a finishing coat of 6 to 8 mm.
What sand do I use for render?
Building (soft) sand, which is finer than the sharp (grit) sand used for concrete and screed. A plasticiser makes the mix easier to work.
More guides
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.