Professional mortar mix calculator for bricklaying and construction projects. Calculate cement, sand, lime and water quantities based on UK standards BS EN 998-2.
Mortar is the bonding agent used between bricks, blocks, and stones in construction. In the UK, mortar specifications follow BS EN 998-2 standards, which classify mortar by compressive strength and composition. Getting the mix ratio right is critical for structural integrity, weather resistance, and longevity.
| Type | Mix Ratio (Cement:Lime:Sand) | Strength | Applications |
|---|---|---|---|
| Type I | 1:0.25:3 or 1:3 | Very High (M12) | Engineering work, manholes, retaining walls, below DPC |
| Type II | 1:0.5:4 to 4.5 | High (M6-M12) | External walls above DPC, exposed locations, loadbearing walls |
| Type III | 1:1:5 to 6 | Medium (M4-M6) | General purpose brickwork, most common mix, internal/external |
| Type IV | 1:2:8 to 9 | Low (M2.5-M4) | Internal walls, weak or historic bricks, low-rise buildings |
| Type V | 1:3:10 to 12 | Very Low (M1-M2.5) | Conservation work, soft heritage bricks, breathable walls |
When you see a ratio like 1:1:6, this represents:
Parts are measured by volume, not weight. Typically, one "part" equals one bucket or shovel.
| Material | Quantity | Coverage (Approximate) |
|---|---|---|
| Standard Brick (215x102.5x65mm) | 1 m² | 60 bricks with 10mm joints |
| Mortar for Brickwork | 1 m³ | Approximately 1,000 bricks |
| Cement (25kg bag) | 1 bag in 1:4 mix | 0.10-0.12 m³ mortar (~100 bricks) |
| Sand (tonne bag) | 1 tonne | Approximately 0.65-0.70 m³ |
| Concrete Block (440x215x100mm) | 1 m² | 10 blocks with 10mm joints |
| Mortar for Blockwork | 25kg cement bag | 12-15 standard blocks |
Our calculator uses industry-standard formulas:
This European standard, adopted in the UK, classifies mortar by compressive strength (M designation) and designates two types:
| Class | Compressive Strength (N/mm²) | Typical Use |
|---|---|---|
| M1 | 1.0 | Very weak, conservation only |
| M2.5 | 2.5 | Weak bricks, internal walls |
| M4 | 4.0 | General purpose, most common |
| M6 | 6.0 | External walls, higher strength |
| M12 | 12.0 | Engineering applications |
Lime has been used in mortar for thousands of years and remains crucial in modern construction:
Types of lime used in UK construction:
Sharp sand (concreting sand) is preferred for mortar strength. Building sand (soft sand) is finer and used with lime mixes. Never use beach sand - salt content destroys mortar.
Dry mix cement, lime and sand for at least 2 minutes before adding water. This ensures even distribution and consistent color. Under-mixing causes weak spots.
Too much water drastically reduces strength and causes shrinkage cracks. Add water slowly until achieving a smooth, buttery consistency that holds its shape.
Cement absorbs moisture from air and loses strength. Use within 3 months of manufacture. Store in dry conditions off the ground. Hardened lumps indicate degraded cement.
Mortar should be slightly weaker than bricks to absorb movement and prevent brick damage. Strong mortar with weak bricks causes the bricks to crack.
Do not work below 3°C or above 30°C. Use frost proofer additives in winter. In hot weather, dampen bricks first and cover finished work to prevent rapid drying.
Use the same measuring method throughout the project for consistent color and strength. Variations in mix ratio create visible color differences in finished work.
Use mortar within 2 hours of mixing (1.5 hours in hot weather). Do not re-temper by adding water - this weakens the mix. Mix small batches frequently.
Creates overly strong mortar that's more rigid than bricks, causing brick damage and cracking. Use correct ratios - more cement is not better. Follow Type III (1:1:6) for general work.
Weakens mortar dramatically, causes shrinkage cracks, and creates color variations. Water/cement ratio should be 0.45-0.55. Add water gradually until achieving proper consistency.
Mortar freezes before curing, destroying bond strength. Water expansion damages mortar structure. Do not work below 3°C. Use frost proofer additives when temperature drops to 5°C.
Creates weak spots, inconsistent color, and poor workability. Dry mix for 2+ minutes before adding water. Ensure thorough mixing to uniform color and texture.
Adding water to hardening mortar severely weakens it. Initial hydration has begun - adding water disrupts chemical process. Mix fresh batches instead of trying to revive old mortar.
Clay, silt, or organic matter in sand reduces strength and increases shrinkage. Always use clean, sharp sand from reputable suppliers. Rinse if contamination suspected.
Joints too thick waste mortar and reduce strength. Too thin creates weak bond. Standard UK joint is 10mm. Consistent joint thickness is crucial for appearance and structural performance.
Newly laid brickwork needs protection from rain, frost, and rapid drying. Cover with plastic sheeting or hessian. Keep slightly damp for first 3-7 days for optimal strength development.
Cement degrades rapidly when exposed to moisture. Lumpy cement has already begun hydrating and has lost strength. Store properly and use within 3 months of manufacture.
Strong mortar with soft heritage bricks causes brick spalling. Weak mortar with engineering bricks creates inadequate strength. Match mortar strength to brick type and exposure conditions.
| Additive | Purpose | When to Use |
|---|---|---|
| Plasticizer | Improves workability, reduces water need | General use, alternative to lime in cement-only mixes |
| Frost Proofer | Lowers freezing point, accelerates setting | Winter work when temperature drops below 5°C |
| Waterproofer | Reduces water penetration | Retaining walls, exposed locations, below DPC |
| Air Entrainer | Creates tiny air bubbles for freeze-thaw resistance | Exposed masonry in harsh climates |
| Coloring Pigments | Changes mortar color to match or contrast with bricks | Aesthetic requirements, heritage matching |
| Accelerator | Speeds up setting time | Cold weather, quick turnaround projects |
| Retarder | Slows setting in hot weather | Summer work, large batches, extended workability |
| Material | Unit | Price Range |
|---|---|---|
| Portland Cement | 25kg bag | £5.50 - £7.50 |
| Sharp Sand (Bulk) | Per tonne | £30 - £50 |
| Sharp Sand (Bagged) | 25kg bag | £3.50 - £5.00 |
| Building Sand (Bulk) | Per tonne | £28 - £45 |
| Hydrated Lime | 25kg bag | £8.00 - £12.00 |
| Ready-Mix Mortar | 25kg bag | £4.50 - £7.00 |
| Plasticizer | 1 litre | £5.00 - £8.00 |
| Frost Proofer | 5 litre | £15.00 - £25.00 |
Note: Prices vary by region, supplier, and quantity. Bulk purchases and trade accounts offer significant savings. Always get quotes from multiple suppliers.
For a typical 10m long × 2.4m high half-brick wall using Type III mortar (1:1:6):
Total material cost: £4×£6.50 + £4×£10 + £40 = £106 approximately
This professional mortar calculator helps UK builders, contractors and DIY enthusiasts accurately calculate cement, sand, lime and water quantities for construction projects. All calculations comply with BS EN 998-2 standards and UK building regulations.
Type I mortar with 1:3 cement:sand ratio (or 1:0.25:3 with lime) is the strongest, achieving M12 compressive strength. However, stronger is not always better - mortar should be slightly weaker than the masonry units to allow flexibility and prevent brick damage.
No. Once mixed, mortar begins the hydration process and must be used within 2 hours (1.5 hours in hot weather). Do not add water to re-temper hardening mortar as this severely weakens it. Mix fresh batches instead and avoid over-mixing large quantities.
Common causes include: excessive water content causing shrinkage, working in hot weather causing rapid drying, insufficient curing protection, using too much cement creating rigid mix, applying to dry bricks that absorb water too quickly, or frost damage during curing.
While not always essential, lime significantly improves workability, water retention, and breathability. It's particularly important for heritage buildings, and creates a more forgiving mix. Modern practice typically uses 1:1:6 (cement:lime:sand) for general purpose work.
Sharp sand (concreting sand) has larger, angular particles providing better strength for mortar and concrete. Building sand (soft sand) is finer with rounded particles, better for bricklaying where workability is important. Many builders use a mix of both for optimal results.
Mortar reaches initial set in 24-48 hours but continues curing for 28 days to reach full strength. Protect new work for minimum 7 days from rain, frost and rapid drying. Avoid loading or stressing new brickwork for at least 3 days.
No. PVA is a bonding agent, not a plasticizer. While PVA can be used as a bonding aid when applied to surfaces before rendering, it should not be added to mortar mix as a plasticizer substitute. Use proper mortar plasticizer or lime for workability.
Light rain after 6+ hours usually causes no harm, but heavy rain on fresh mortar (under 6 hours old) can wash out cement, weaken joints, and cause staining. Always cover new work with plastic sheeting if rain is forecast within 24 hours.
Expert Reviewed — This calculator is reviewed by our team of financial experts and updated regularly with the latest UK tax rates and regulations. Last verified: January 2026.
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