What is mortar made from?

Mortar is made from a binder mixed with sand and water. The most common binders are Portland cement, hydraulic lime, or a combination of both. The mix ratio determines the strength: a 1:3 cement:sand mortar is strong and used in exposed or structural applications; a 1:1:6 cement:lime:sand is weaker and more flexible, suitable for standard brickwork; a pure lime mortar (1:2.5 lime:sand) is used for historic masonry.

What mortar mix should I use for brickwork?

The mix depends on the exposure and the brick type. A 1:1:6 (cement:lime:sand) or 1:4 (masonry cement:sand) mix suits most standard external brickwork. More exposed positions such as coping and chimney stacks use a 1:0.5:4.5 or 1:3 mix. Soft or handmade bricks and all work to pre-1919 buildings require a lime-based mortar - never a strong cement mix, which causes brick face spalling.

What is the difference between lime mortar and cement mortar?

Cement mortar is strong and rigid, setting quickly and permanently. Lime mortar is softer, more flexible, and breathable - it allows moisture to evaporate from the wall and sacrificially erodes before the masonry units do. Historic buildings require lime mortar because the softer bricks cannot tolerate the rigid constraint of cement mortar, which traps moisture and causes spalling and structural cracking.

Mortar - Construction Glossary

Definition

Mortar is a workable paste made from a binder - cement, hydraulic lime, or a combination of both - mixed with sand and water. In masonry construction it is used to bond bricks, blocks, or stone together, fill the bed and perpend joints between units, and distribute load evenly across the wall. Once set, it provides structural continuity and weatherproofing to the masonry assembly.

In practice

Mortar strength must be matched to the masonry units. The critical rule is that mortar must never be stronger than the bricks or stone it bonds - a stronger mortar will cause the masonry units to crack or spall as the wall moves rather than allowing the mortar joints to flex and erode sacrificially. Common mixes: 1:3 cement:sand for exposed locations and engineering bricks; 1:1:6 cement:lime:sand for standard facing brickwork; 1:2.5 hydraulic lime:sand for pre-1919 or soft brick.

Mortar has a working life (pot life) of around 1-2 hours after mixing - after this it begins to stiffen and should not be retempered with additional water. In cold weather (below 3°C), bricklaying should stop or frost protection be provided as freezing before the mortar has set will destroy the bond. Ready-mixed retarded mortar (silo mortar) is widely used on larger sites, with a working life of several days.

Building Regulations

StandardBS EN 998-2 - Specification for masonry mortar

Lime mortar standardBS EN 459 - Building lime

Cold weather workingBelow 3°C - protect or suspend bricklaying

Mortar specification forms part of the structural design for masonry walls under Approved Document A. BS EN 998-2 classifies mortars by designation (M2 to M20) rather than the traditional ratio system. For listed buildings, mortar specification must be agreed with the local planning authority's conservation officer before works begin.

Full Building Regulations guidance

Related Calculators

Masonry Mortar Calculator Brick Calculator

Mortar

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