Mortar Mix Ratio: The Right Sand and Cement Mix for UK Bricklaying

Mortar is measured as cement to sand by volume, sometimes with lime added. Here's what's actually used on UK sites:

1:3 — Below DPC, chimneys, copings, retaining walls. Strongest, least forgiving.

1:4 — Exposed façades, parapets, coastal/severe weather. Durable general external.

1:5 — Most house brickwork above DPC. The everyday all-rounder.

1:6 — Internal walls, sheltered blockwork. Weaker, very workable.

1:1:6 (cement:lime:sand) — Soft or historic brick, breathable walls. Traditional, flexible.

If you build nothing but house extensions, you'll spend most of your life in 1:5 and 1:6, dropping to 1:3 or 1:4 for anything below ground or badly exposed. These map onto the older BS 5628 mortar designations (i) to (v) and the current BS EN 998-2 masonry mortar standard.

This is the one that separates a wall that lasts from one that cracks. Mortar should always be weaker than the bricks it joins.

Walls move — thermal expansion, ground settlement, moisture. In a well-built wall, that movement is absorbed by the soft mortar joints, which is why old lime-mortar walls can flex for centuries without a crack. Put a rock-hard 1:3 mortar around ordinary facing bricks and the movement has nowhere soft to go, so it cracks straight through the bricks instead. A cracked brick is a far bigger problem than a cracked joint: you can rake out and repoint a joint, but a spalled brick face means replacing the unit.

So when you're tempted to "go a bit stronger to be safe", don't. Match the mix to the masonry.

Traditional mortar used lime for workability and flexibility. Modern mortar mostly uses a liquid plasticiser added to the gauging water, which entrains tiny air bubbles and makes the mix buttery without needing lime.

For everyday cement:sand brickwork, plasticiser is fine and it's what most gangs use. But lime still wins on two jobs: soft or historic bricks, where a rigid cement mortar would damage the masonry, and any wall you want to stay breathable so trapped moisture can escape. A 1:1:6 cement:lime:sand mix is the classic choice there. For genuine conservation work on pre-1919 buildings, you may need a pure lime mortar with no cement at all, which is a specialist area.

Bricklaying mortar traditionally uses soft building sand (also called bricklaying sand), because its fine, rounded grains make a smooth, workable mix that tools nicely. Sharp sand gives a stronger, coarser mortar and is used for below-ground work, screeds and where extra strength matters. Plenty of bricklayers blend the two, or use a ready-blended bricklaying sand from a merchant like Travis Perkins or Jewson.

Whatever you pick, keep it consistent across the job. Switching sand halfway changes the mortar colour, and on a face wall that shows.

The ratio tells you the proportions; the wall size tells you the amount.

A single-skin brick wall needs about 0.03 m³ of mortar per m² (roughly 60 bricks). A one-brick wall needs about 0.055 m³ per m². Add 15% wastage — bricklaying is messy. At 1:5, that works out to roughly 8 bags of cement and a tonne of sand per 1,000 bricks.

Worked example — a 10 m² single-skin garden wall at 1:5 with 15% wastage: bricks 10 × 60 = 600; mortar 10 × 0.03 = 0.30 m³, +15% = 0.35 m³; cement about 5 × 25 kg bags; soft sand about 0.6 tonnes (one bulk bag). At 2026 merchant prices, that's roughly £30 of cement and £52 of sand, plus a tub of plasticiser.