Repointing calculator: mortar for pointing
The calculator needs JavaScript. The worked example, formula and figures below show exactly how it works, so you can do the sum yourself. A guide, not advice. Check your supplier's or maker's figures before ordering.
Short answer
Worked example
| You enter | Value |
|---|---|
| What are you repointing? | Brickwork |
| Area to repoint | rectangle 5 m × 2 m |
| Brick or slab length | 215 mm |
| Brick height or slab width | 65 mm |
| Joint width | 10 mm |
| Depth raked out | 15 mm |
| Binder | Cement |
| Parts sand to 1 part binder | 5 parts |
| Waste allowance | 0% |
| Dry-volume factor | 1.3 × |
| Binder density | 1,440 kg/m³ |
| Sand density | 1.5 t/m³ |
| Binder bag size | 25 kg |
Order: 1 × bags of binder and 42 kg of sand
| Result | Value |
|---|---|
| Binder bags | 1 |
| Binder (cement or lime) | 8 kg |
| Sand | 41.9 kg |
| Mortar (wet volume, with waste) | 0.026 m³ |
| Joints as a share of the face | 17.19% |
| Joint length | 177.78 m |
| Area | 10 m² |
Show the working
- Joint share: ((0.215 + 0.01) × (0.065 + 0.01) − 0.215 × 0.065) ÷ ((0.215 + 0.01) × (0.065 + 0.01)) = 0.171852
- Wet mortar: 10 m² × 0.171852 × 15 mm × 1 (0% waste) = 0.025778 m³
- Joint length: 10 × (1 ÷ 0.225 + 1 ÷ 0.075) = 177.8 m
- Dry volume: 0.025778 × 1.3 = 0.033511 m³
- Binder: 0.033511 ÷ (1 + 5) × 1,440 kg/m³ = 8 kg
- Sand: 0.033511 × 5 ÷ (1 + 5) × 1.5 t/m³ = 42 kg
- Binder bags: 8 kg ÷ 25 kg, rounded up = 1
How it works
- Joint share of the face = ((L + j)(H + j) − L·H) ÷ ((L + j)(H + j))
- Wet mortar (m³) = area × joint share × depth raked out × (1 + waste); dry = wet × dry-volume factor
- Binder (kg) = dry ÷ (1 + r) × binder density; sand (kg) = dry × r ÷ (1 + r) × sand density × 1,000
- Joint length (m) = area × (1 ÷ (L + j) + 1 ÷ (H + j))
Raking out and cutting mortar makes silica dust: see the silica exposure calculator.
Lime mixes are labelled for older solid walls; ask a conservation specialist for listed buildings.
Our default (adjustable)
These are typical planning figures and our own allowances, not facts about your product. Change any of them in the calculator to match your bag, pack or tin.
| Figure | Our default (adjustable) | Kind | Source |
|---|---|---|---|
| Brick or slab length: Brickwork | 215 mm | Common UK size Not yet checked against the source | From your product UK standard brick (work size). |
| Brick height or slab width: Brickwork | 65 mm | Common UK size Not yet checked against the source | From your product UK standard brick (work size). |
| Brick or slab length: Patio joints | 600 mm | Common UK size Not yet checked against the source | From your product brief v2 L1 (PA1: 600 × 600 slab). Slabs vary; check the product. |
| Brick height or slab width: Patio joints | 600 mm | Common UK size Not yet checked against the source | From your product brief v2 L1 (PA1: 600 × 600 slab). Slabs vary; check the product. |
| Joint width | 10 mm | Common UK size Not yet checked against the source | From your product Standard UK mortar joint. |
| Parts sand to 1 part binder: Cement | 5 parts sand to 1 cement | Our assumption Not yet checked against the source | Our choice: change it to suit your job Check your maker's or builder's spec; the right ratio depends on the job. |
| Binder density: Cement | 1440 kg/m3 | Our assumption Not yet checked against the source | Our choice: change it to suit your job Typical planning figure with no source yet. Researcher to source it and reclassify as typical. |
| Binder bag size: Cement | 25 kg | Common UK size Not yet checked against the source | From your product Common UK cement bag. |
| Parts sand to 1 part binder: NHL 3.5 lime | Enter from the bag, pack or tin | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 B3: lime ratios from SPAB / Historic England guidance (Researcher). |
| Binder density: NHL 3.5 lime | Enter from the bag, pack or tin | Typical value Not yet checked against the source | From your product brief v2 B3: NHL lime bulk density. Researcher to source (lime maker's data). |
| Binder bag size: NHL 3.5 lime | Enter from the bag, pack or tin | Common UK size Not yet checked against the source | From your product brief v2 B3: NHL bag size, from the bag. |
| Parts sand to 1 part binder: NHL 5 lime | Enter from the bag, pack or tin | Our assumption Not yet checked against the source | Our choice: change it to suit your job brief v2 B3: lime ratios from SPAB / Historic England guidance (Researcher). |
| Waste allowance | 10 % | Our assumption Not yet checked against the source | Our choice: change it to suit your job Droppings and mixing loss. |
| Dry-volume factor | 1.3 × | Our assumption Not yet checked against the source | Our choice: change it to suit your job Dry materials shrink when mixed with water. Researcher to check against cement makers' guidance. |
| Sand density | 1.5 t/m3 Sources range 1.4–1.6 t/m3 | Typical value Not yet checked against the source | aggregatecalculator.co.uk aggregate density table (checked 19 October 2026) |