Getting your mortar mix ratio right is one of the most important factors in a long-lasting brickwork, tiling or render job. Too strong and the mortar can crack or damage the masonry. Too weak and it crumbles. This guide covers the right mix for every common application.
Once you know your ratio, use our free Mortar Calculator to work out exactly how much cement and sand you need.
What Is a Mortar Mix Ratio?
A mortar mix ratio describes the proportion of cement to sand by volume. A 1:4 mix means one part cement to four parts sand. The higher the sand proportion, the weaker and more workable the mix — but also the more likely it is to be flexible, which is actually desirable in some applications such as internal render where movement needs to be accommodated.
Common Mix Ratios and When to Use Them
| Mix Ratio | Strength | Best For |
|---|---|---|
| 1:3 | Very strong | Engineering brickwork, below DPC, copings, pointing in exposed locations |
| 1:4 | Strong | General brickwork, blockwork, bed joints, external applications |
| 1:5 | Medium | External render scratch coat, paving, flooring screeds |
| 1:6 | Weak / flexible | Internal render, lightweight blockwork, internal floor screeds |
Brickwork Mortar
For most standard UK brickwork — garden walls, house extensions, outbuildings — a 1:4 cement:sand mix is the go-to choice. It is strong enough for weather exposure but not so rigid that it cracks under minor settlement.
For brickwork below the damp-proof course (DPC), or in very exposed coastal or upland locations, step up to a 1:3 mix for greater resistance to moisture penetration and freeze-thaw damage.
Avoid using neat cement (no sand) — it shrinks badly as it cures and will crack away from the bricks. Always use the correct sand type: soft (builder’s) sand for general brickwork mortar, and sharp (coarse) sand for floor screeds and render base coats.
Tile Adhesive vs Sand and Cement Mortar
Most modern tiling is done with ready-mixed or powder adhesive rather than traditional sand and cement mortar. However, sand and cement is still widely used for:
- Large format floor tiles — where a thick mortar bed (15–50mm) is needed to level an uneven substrate
- External paving — where a semi-dry mortar bed is the standard method
- Natural stone — where adhesives may not provide sufficient bond strength
For a traditional mortar bed under floor tiles, use a 1:4 or 1:5 mix with sharp sand, applied at 10–15mm depth for an even substrate.
Render Mix Ratios
Wall render is typically applied in two or three coats, with each coat getting slightly weaker than the last to reduce the risk of cracking:
- Scratch coat (first coat): 1:4 cement:sand — applied to the bare masonry, scratched to provide a key
- Float coat (second coat): 1:5 or 1:6 — a flatter, more workable coat that forms the main body of the render
- Finish coat: 1:6 or proprietary finish plaster — the final smooth or textured surface coat
Adding a plasticiser to your render mix improves workability and reduces the water demand, which in turn reduces the risk of shrinkage cracking.
How Much Mortar Do I Need?
Once you have chosen your mix ratio, use our Mortar Calculator to get exact quantities of cement and sand in kilograms and 25kg bags. It covers brickwork, floor tiling, wall render and paving, and includes a wastage allowance to make sure you do not run short on the job.
