How this calculator works
Render is a mix of building sand and cement, spread on a wall to a depth of about 15 to 20 mm. The volume of render is the area of the wall times the thickness (in metres), plus your waste allowance. The sand and cement bulk up when they are wetted, so you need about 1.3 times the finished volume of dry materials. A mix of 4 to 1 is four parts of sand to one part of cement by volume, so a fifth of the dry volume is cement. Cement weighs about 1,440 kg per cubic metre, and building sand about 1,600.
Worked example: a wall 8 × 3 m with 4 m² of windows is 20 m² to render. At 20 mm thick with 15% waste that is 0.46 m³ of render. At a 4 to 1 mix you need 172 kg of cement (7 bags of 25 kg) and 0.77 tonnes of building sand. At 15 mm it is 6 bags, and at 25 mm 9 bags. A richer 3 to 1 mix needs 9 bags and a leaner 6 to 1 mix 5. A larger wall of 12 × 5 m needs 20 bags and 2.1 tonnes of sand.
Cement and sand to render a wall (4 : 1 mix, 15% waste, 4 m² of openings)
For 15 mm and 20 mm thick render.
| Wall | Area | Render at 20 mm | Cement bags at 20 mm | Sand at 20 mm | Cement bags at 15 mm |
|---|---|---|---|---|---|
| 4 × 2.4 m | 5.6 m² | 0.13 m³ | 2 | 0.21 t | 2 |
| 6 × 2.4 m | 10.4 m² | 0.24 m³ | 4 | 0.40 t | 3 |
| 8 × 3 m | 20.0 m² | 0.46 m³ | 7 | 0.77 t | 6 |
| 10 × 3 m | 26.0 m² | 0.60 m³ | 9 | 1.00 t | 7 |
| 12 × 5 m | 56.0 m² | 1.29 m³ | 20 | 2.14 t | 15 |
| 15 × 6 m | 86.0 m² | 1.98 m³ | 30 | 3.29 t | 23 |
Tips before you buy
- Clean the wall and remove loose paint, dust and anything that stops the render sticking. Wet a dry, porous wall before you start.
- Render in two coats: score the base coat to give the finish coat something to grip, and let it firm up before the second coat.
- Use a mix that is no stronger than the wall: a rich mix on weak brick or stone can crack and pull the face away.
- Do not render in frost or hot sun, and protect the new render from rain, wind and sun while it cures.
- Use a bonding agent or a primer on smooth or painted surfaces, and beads at the corners and the base.
Tools & materials for this project
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Frequently asked questions
How much sand and cement do I need to render a wall?
For a wall of 20 m² at 20 mm thick, with a 4 to 1 mix and 15% waste, about 7 bags of 25 kg cement and 0.8 tonnes of building sand. That is about 8.6 kg of cement per square metre of wall.
What is the best mix for rendering a wall?
A 4 to 1 mix (four parts of building sand to one of cement) is a general-purpose choice, with a 3 to 1 base coat for exposed walls and a leaner 5 to 1 or 6 to 1 finishing coat. The render should be no stronger than the wall.
How thick should render be?
About 15 to 20 mm in total, applied in two coats: a base coat of 10 to 12 mm and a finishing coat of 6 to 8 mm. Thicker render on a very uneven wall costs more and is harder to apply.
How many bags of cement for 10 square metres of render?
About 4 bags at 20 mm thick and 4 to 1, with 15% waste.
Can I use soft sand or sharp sand for render?
Use building (soft) sand for render and mortar. Sharp (grit) sand is coarser and is used for concrete and screed.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.