Mortar Mix Ratio & Quantity Calculator
Calculate the exact quantities of cement, sand, and water for any mortar mix — bricklaying, pointing, rendering, or plastering — at any mix ratio.
Mortar Mix Guide
Mortar Mix Ratios by Application
Mortar strength must match the application. Too strong a mortar damages softer masonry by trapping moisture. Bricklaying (internal): 1 cement: 5 sand. Bricklaying (external): 1 cement: 4 sand. Repointing (hard brick): 1 cement: 3 sand. Repointing (soft brick or stone): 1 lime: 2.5 sand (softer, sacrificial — protects the masonry). External rendering: 1 cement: 4 sand (scratch coat), 1 cement: 5 sand (finish coat). Paving bedding mortar: 1 cement: 4 sharp sand. Floor screed: 1 cement: 4 sharp san
Mixing Technique
Always mix dry materials first before adding water. Measure by volume using a bucket, not by weight on site. Mix to an even colour before adding water — incomplete dry mixing produces weak spots. Water addition: add approximately 80% of the expected water and mix thoroughly, then add remainder to achieve the right consistency. Correct consistency: mortar should hold its shape when squeezed in the hand but not stick to clean surfaces. Too wet: runs off the trowel, poor adhesion, shrinkage crackin
Ready-Mixed vs Site-Mixed Mortar
Ready-mixed mortar (tub, dry bags, or pre-batched wet): convenient, consistent, no mixing equipment needed. Dry bag mortar (just add water): good for small jobs. Pre-batched wet mortar in tubs: includes a retarder that keeps mortar workable for up to 36 hours — excellent for larger jobs. Site mixing: economical for large quantities (1 tonne of bricklaying mortar costs approximately £35 mixed vs £80-120 pre-mixed). For repointing: always use a pre-mixed repointing mortar or mix carefully to match
Lime Mortar vs Cement Mortar
Traditional lime mortar (NHL 3.5 or NHL 5 natural hydraulic lime + sand) should be used for repointing all pre-1920 brick and stone buildings and any soft brick regardless of age. Cement mortar is too rigid and too impermeable for soft or historic masonry — it traps moisture and causes spalling (surface crumbling). Lime mortar is sacrificial — it slowly wears away and can be repointed rather than damaging the surrounding masonry. If you see crumbling, spalling, or blown brickwork, suspect incorr
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