BS EN 998-2 — Masonry Mortar

What BS EN 998-2 covers

It governs masonry mortars by performance, not just a recipe — the key shift the standard introduced. A 'designed' mortar is factory-made and the manufacturer guarantees the strength class (e.g. certified M6); a 'prescribed' mortar is a site-mixed recipe (e.g. 1:4 cement:sand) where the strength is assumed from the proportions rather than tested.

For commercial or structural work a designed mortar is often specified, because site-mixed prescribed mortars vary with sand quality, moisture and batching accuracy — the same nominal 1:4 mix can drift in strength depending on how the sand is gauged (sand 'bulks' when damp).

Mortar should be the sacrificial element of the wall — weaker than the masonry units, not stronger. In the UK freeze–thaw climate, moisture must be able to escape through the joints; if the mortar is harder than the brick, moisture is trapped in the brick face and the face spalls (chips off) when it freezes. A correctly specified joint is designed to be repointed periodically rather than allowing the bricks themselves to fail.

Pre-1919 solid-wall buildings generally need a softer lime mortar (NHL) rather than a cement mortar, to stay weaker and more breathable than the historic brick and allow movement.

For exposed or severe-exposure masonry, air-entrained (plasticised) mortar is generally specified — the entrained air gives the set mortar room to accommodate frost expansion and improves freeze–thaw durability.

BS EN 998-2 also requires manufacturers to declare the mortar's workable life (how long it stays usable after mixing) — a practical site-management detail when planning a day's bricklaying.

The standards page covers how mortar is classified and why it behaves as it does; the quantity maths stays on the tool — use the mortar calculator to work out sand and cement for your wall area and mix.