The mortar should always be softer and more permeable than the bricks or stone it sits between. On older solid-walled houses built in lime, that usually means repointing in lime mortar, because hard cement pointing can trap moisture and damage the faces of soft bricks and stone.
Pointing is the mortar in the joints you see on the face of the wall. It’s there to keep the weather out and to let the wall breathe. Get it right and it’ll protect the wall for decades. Get it wrong and it can cause damp and damage the bricks.
The golden rule
Mortar should be the sacrificial part of the wall. It should be slightly softer and more permeable than the masonry, so that moisture and salts move out through the joints and, if something has to wear, it’s the mortar that you can rake out and replace, not the bricks.
What goes wrong with cement on old walls
- Moisture gets trapped. Hard cement pointing is much less permeable than soft bricks and stone, so moisture in the wall tries to escape through the masonry instead of the joints.
- The bricks get damaged. As that moisture evaporates or freezes at the brick face, the faces can crumble and flake off, a problem called spalling. You’ll often see bricks eroding while the cement pointing stands proud.
- It cracks away. Rigid cement doesn’t move with the wall, so fine cracks open up along the joint edges and let rain in behind it.
On older houses originally built with lime mortar, which is most houses before roughly the early to mid twentieth century, lime is usually the right choice for repointing. On more modern cavity walls built with cement-based mortar and harder bricks, a suitable cement-based mortar is normal.
Signs your pointing needs attention
- Mortar recessed deep into the joints or crumbling out.
- Cracks along the joint edges.
- Hard cement pointing on soft, eroding bricks or stone.
- Damp patches on the inside of the wall that worsen after rain.
Doing it properly
- Rake out to a sensible depth, not just a skim on the surface.
- Match the mortar to the masonry, both in strength and look.
- Don’t use power tools that damage the arrises, the edges of the bricks.
- Protect fresh lime mortar from frost, rain and fast drying while it cures.
If a wall has had damp from failed pointing, allow plenty of drying time after repointing before deciding whether any internal work is needed.
When to call a specialist
If you have damp on an older wall and aren't sure whether the pointing is to blame, get the wall looked at before choosing a mortar or a treatment. Book a survey with All Dry on 01226 287181 or email info@alldrydampproofing.com.
Frequently asked questions
Can bad pointing cause damp?
Yes, eroded or cracked pointing can let rain into the wall.
Why are my bricks crumbling next to cement pointing?
Hard pointing can force moisture out through the brick faces, causing them to spall.
Is lime pointing more expensive?
It can take more care to apply and cure, but on older walls it usually protects the masonry better.