Lime mortar is a mortar in which lime is the binder, mixed with sand and water. It is used for masonry and plastering. Lime mortar is softer, more flexible and more vapour-open than cement mortar, and hardens more slowly. This makes it especially suited to historic and listed work with soft bricks.
Properties
- Vapour-open — moisture can escape from the wall through the joints and plaster, preventing damp build-up
- Soft and flexible — small movements of the masonry are taken up by the mortar rather than the brick; air-lime mortar has a mild self-healing action on hairline cracks
- Slow hardening — air-lime mortar hardens by absorbing carbon dioxide (carbonation) and so needs time and air
- Lower strength — lime mortar is weaker than cement mortar and, when young, still vulnerable to frost
Application
Lime mortar is the logical choice when restoring or repointing old walls: it is softer than the brick, so the joint, not the stone, takes up the stresses. Cement mortar is too hard for this and can make soft, historic bricks crumble.
Points to note
- Do not work lime mortar in frost
- Keep it moist while it sets and let it harden slowly
Related terms
- Lime
- Lime putty
- Mortar
- Masonry
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.