Mortar Mix Ratio Calculator (Sand:Cement)

Mortar Mix Guide (UK)

What's the difference between Mortar and Concrete?

Mortar bonds masonry units (bricks, blocks, stone). Concrete forms structural elements (foundations, slabs). Key differences: mortar uses fine aggregate (sand) only — no coarse aggregate. Concrete uses both sand and gravel. Mortar must be workable (spread cleanly with a trowel, support a brick without slumping) but firm enough to support load above. Cement-only mortars (1:3 cement:sand without lime) are too brittle — crack as walls move slightly. Always include lime or plasticiser for workability and flexibility in mortar — a rigid, cement-only mix will crack as the wall naturally moves slightly over time.

What's the difference between Lime and Plasticiser?

Traditional mortars use hydrated lime as the third component. Lime adds: workability (mortar spreads cleanly). Plasticity (forgiving during laying, slow setting). Crack tolerance (some flex through seasonal movement). Bond improvement to absorbent units. Modern mortars often substitute plasticiser (Feb-Mix, Sika-Air) for lime: cheaper. Faster to mix (no slaking time). Same workability benefits. Substitute ratio: typically 50-100ml plasticiser per 25kg cement. Lime mortar specifics: hydrated lime, typically CL90 grade, is the standard choice for most traditional masonry repair and repointing work.

What do I need to know about Workability and Mixing?

Good mortar should: hold a sharp edge when trowelled. Spread cleanly without dragging. Support a brick without slumping. Stiffen progressively as it sets (workable 1-2 hours from mixing). Common DIY mistakes: too much water (drops strength dramatically). Mixing too large a batch (sets before fully used). Using wrong sand (soft/plastering sand for brickwork makes weak mortar — use sharp/building sand). Sand quality: building sand (sharp sand): for brickwork mortar. Sharp particles bond strongly with cement, giving a stronger, more durable mortar than soft or rounded sand grains would produce.

What's the key thing to understand about Coverage and Quantity?

Approximate mortar usage per m² of wall: standard 215×65mm brick wall, 10mm joints: 0.025 m³ mortar per m² (half-brick wall). Or about 60 bricks/m². Solid 215mm wall: 0.045 m³ per m². 100mm block wall: 0.015 m³ per m². 140mm or 215mm block wall: 0.020-0.025 m³ per m². Working ratios: 1m³ mortar contains approximately: 1.6 tonnes sharp sand. 250kg cement (1:6 mix with plasticiser) OR 200kg cement + 50kg hydrated lime (1:0.5:4.5 with lime). ~150 litres water. Practical batching: a typical 1m³ wheelbarrow batch will produce enough mortar for a substantial day's bricklaying, though exact coverage varies with joint thickness and brick size.