Mortar Calculator
Calculate sand and cement for bricklaying mortar, repointing and render. All mix ratios with BS EN 998-2 designations, door and window deductions, delivery options and plasticiser. 2026 UK pricing.
Single skin: 102.5mm brick on edge. Standard for garden walls and partition walls.
1:4 (M6) is standard for most brickwork and blockwork. BS EN 998-2.
0.9×2.0m each
1.2×1.0m each
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| Ratio (cement:sand) | BS EN 998-2 Class | Strength (N/mm²) | Typical Application |
|---|---|---|---|
| 1:3 | M12 | ~12 | Engineering brick, foundations below DPC, chimney stacks, copings |
| 1:4 | M6 | ~6 | Standard brickwork and blockwork — most common UK domestic mix |
| 1:5 | M4 | ~4 | Soft stock brick, internal walls, low-stress work |
| 1:6 | M2 | ~2 | Repointing, soft pre-1919 brick (where lime not strictly required) |
| 1:1:6 (cement:lime:sand) | M4 | ~4 | Traditional gauged mortar — better workability and breathability |
| 1:2:9 (cement:lime:sand) | M2 | ~2 | Heritage repointing, soft stock brick |
| NHL 3.5 (lime:sand 1:3) | — | ~3.5 | Pre-1919 solid wall repointing — moderate exposure |
| NHL 2 (lime:sand 1:3) | — | ~2 | Pre-1919 repointing — sheltered/internal only |
| Number of Bricks | Wall Area (single skin) | Mortar Volume | Building Sand | Cement (25kg bags) |
|---|---|---|---|---|
| 100 bricks | ~1.7 m² | 0.07 m³ | 0.09 t | 1 bag |
| 250 bricks | ~4.2 m² | 0.17 m³ | 0.22 t | 2 bags |
| 500 bricks | ~8.4 m² | 0.34 m³ | 0.44 t | 4 bags |
| 1 pack (~400) | ~6.7 m² | 0.28 m³ | 0.35 t | 3 bags |
| 1000 bricks | ~16.8 m² | 0.69 m³ | 0.89 t | 8 bags |
| 1 pallet (~500) | ~8.4 m² | 0.34 m³ | 0.44 t | 4 bags |
| Masonry Unit | Recommended Mix | BS Class | Why |
|---|---|---|---|
| Engineering brick (Class A/B) | 1:3 cement:sand | M12 | Hard, dense brick — strong mortar required to match compressive performance |
| Facing brick (modern fired clay) | 1:4 | M6 | Standard residential brickwork — the default mix |
| Common/concrete brick | 1:4 | M6 | Hidden work, internal walls, foundations above DPC |
| Soft stock brick (pre-1919) | 1:1:6 cement:lime:sand | M4 | Lime softens the mix to match the brick — prevents face spalling |
| Reclaimed handmade brick | NHL 3.5 lime mortar | — | Portland cement is too hard and traps moisture, damaging the brick |
| Concrete block (dense) | 1:4 | M6 | Standard for solid wall and partition blockwork |
| AAC block (Thermalite, Celcon) | 1:1:6 or thin-joint | M4 | Aerated blocks are lightweight — softer mortar avoids cracking |
| Sandstone / limestone | NHL 3.5 lime mortar | — | Stone requires lime mortar for breathability and movement |
Mix Guide
Mortar Mix Ratios & Standards
Mix ratios and BS EN 998-2 designations
Mortar mixes are designated by compressive strength class under BS EN 998-2 (Specification for masonry mortar). The class relates to the minimum compressive strength in N/mm² at 28 days. Common site mixes are approximately: 1:3 → M12 (~12 N/mm²), 1:4 → M6 (~6 N/mm²), 1:5 → M4 (~4 N/mm²), 1:6 → M2 (~2 N/mm²).
General rule: the mortar must always be weaker than the masonry unit. Using a mix that is stronger than the brick causes stresses to concentrate in the brick face rather than the joint, leading to spalling and cracking. For older soft bricks, M2 or M4 is often the maximum appropriate strength.
Repointing — the correct approach
Rake out old mortar to a minimum 20mm depth to ensure adequate bond. Use a cold chisel or mortar raker drill bit — never an angle grinder on old soft brick as it destroys the arrises. Brush out all dust and dampen the joint before applying fresh mortar.
For post-1919 hard engineering bricks, a 1:4 or 1:5 mix is appropriate. For pre-1919 soft stock brick, use NHL (natural hydraulic lime) 3.5 or 2 as the binder instead of Portland cement. Do not use cement-based mortar on lime-based original jointing — the differential movement will crack the brickwork.
| Sand Type | BS Reference | Use For | Do Not Use For |
|---|---|---|---|
| Building sand (soft sand) | BS EN 13139 | Bricklaying mortar, repointing, render scratch coat | Concrete, floor screed |
| Sharp sand (concreting sand) | BS EN 12620 | Concrete, floor screed, rough cast render mix | Bricklaying mortar (too harsh, unworkable) |
| Plastering sand (washed) | BS EN 13139 | Render finish coats, fine pointing | Structural concrete |
| Kiln-dried sand | BS EN 13139 | Block paving joints only | Any wet mortar mix |
| Silver sand | BS EN 13139 | Coloured/decorative mortar, fine pointing | Structural brickwork |
Sand types — building sand vs sharp sand
Building sand (soft sand, BS EN 13139) has rounded grains that give mortar its workable, 'fatty' consistency. It is the correct sand for bricklaying mortar, repointing and most render mixes. Sharp sand (BS EN 12620) has angular grains intended for concrete and floor screeds — it produces a harsh, unworkable mortar that is very difficult to tool.
Exception: some rough cast and pebbledash render mixes use a blend of building sand and sharp sand (typically 2:1) for additional texture. Fine sharp sand is also sometimes used for pointing dense engineering brickwork where extra durability is required.
Plasticiser — why and how much
Plasticiser (air-entraining admixture) improves mortar workability by introducing tiny air bubbles that lubricate the mix. The result is a smoother, more consistent mortar that is easier to spread, less likely to crack from frost action, and has better water repellence when cured. Approximately 1 litre covers 5–6 tonnes of sand.
Do not use washing-up liquid as a plasticiser substitute — it produces an unstable foam that collapses on drying, leaving voids in the mortar bed and dramatically reducing strength. Always use a purpose-made mortar plasticiser such as Febmix or equivalent.
FAQ
Common Questions
For most domestic brickwork, a 1:4 cement:building sand mix (BS EN 998-2 class M6) is standard. Use 1:3 (M12) for structural or exposed work below the DPC, chimney stacks or engineering brickwork. Use 1:5 or 1:6 (M2–M4) for softer bricks or repointing where the mortar must be weaker than the masonry unit.
For single-skin brickwork (102.5mm) with 10mm joints: approximately 0.022 m³ of mortar per m² of wall face (0.024 m³ with 10% wastage). For double-skin brickwork: approximately 0.044 m³/m². For 100mm blockwork: approximately 0.013 m³/m². These are the figures used by our calculator.
Yes — pre-1919 brick and stone buildings were built with lime mortar. Repointing with Portland cement traps moisture in the wall and causes the brick face to spall. Use NHL (natural hydraulic lime) 2 or 3.5 instead. For listed buildings, check with your local authority as specific mortar specifications may be required.
Yes — mortar plasticiser improves workability, frost resistance and reduces water permeability. Add approximately 60–90ml per 25kg bag of cement. Do not use washing-up liquid as a substitute — it creates unstable voids that weaken the mortar. Purpose-made plasticisers such as Febmix or Cementone are the correct product.
Use building sand (also called soft sand, BS EN 13139) for all bricklaying, blockwork and repointing mortar. Building sand has rounded grains that produce a smooth, workable, "fatty" mortar. Never use sharp sand (BS EN 12620) for mortar — its angular grains produce a harsh, unworkable mix that cannot be tooled cleanly. Sharp sand is for concrete and floor screed only.
For 500 standard UK bricks (215×102.5×65mm) with 10mm joints, you need approximately 0.34 m³ of mortar — about 0.44 tonnes of building sand and 4 × 25kg bags of cement at a 1:4 mix, including 10% wastage. For 1000 bricks, double these figures.
Engineering bricks (Class A and Class B to BS EN 771-1) are denser and stronger than facing brick, so they need a stronger mortar to perform as designed. Use a 1:3 cement:building sand mix (BS EN 998-2 class M12) for engineering brick used structurally, below DPC, in chimney stacks or in coping courses. For engineering brick in general above-ground walling, 1:4 (M6) is acceptable but 1:3 is preferred.
Cracking usually indicates one of four issues: (1) the mortar is stronger than the brick — common when using 1:3 on soft stock or pre-1919 brick; (2) retempering — adding water to mortar that has started to set, which destroys the cement bond; (3) drying too quickly in hot or windy weather — dampen the bricks before laying and keep new work shaded; (4) frost damage during the first 48 hours — never lay mortar when temperatures will fall below 3°C overnight. Always match mortar strength to the masonry, and never mix on a hot day without protecting the work.