Repointing: lime or cement?

Mortar is meant to be the weakest part of a wall. When it wears out, you rake it out and replace it. When the brick wears out, you have a much bigger job. Choosing the right mortar when you repoint is what keeps it that way round.

What repointing involves

Repointing means raking out the old, failing mortar to an even depth, usually 15 to 20 mm, and packing new mortar back into the joints. Done well, the wall looks as if it was always that way. Done badly, mortar smears across the faces and traps water where it can do damage.

Why lime for old walls

Most Melbourne houses built before the 1940s were laid in lime mortar. Lime is softer than the brick, flexible enough to move with the seasons and porous enough to let moisture escape through the joints.

Repoint those walls in hard cement and the moisture has nowhere to go but through the brick. Salts build up behind the face, and after a few winters the faces start to flake. We see it most on Victorian and Edwardian fronts that were patched in the 1970s and 80s.

Why cement for new work

Modern bricks are fired harder and are much denser, and a cement-based mortar suits them. It is stronger, sets faster and matches the way the wall was designed to work. A soft lime mix on a modern wall would simply wear out sooner.

How to tell which your wall needs

Age is a good clue, but it isn’t the whole story. We look at four things:

• Age: a house built before the Second World War was almost certainly laid in lime

• Scratch test: lime mortar crumbles to a sandy powder under a key, cement resists it

• Colour: original lime joints tend to be soft cream or grey, not hard and bright

• Where the damage is: crumbling brick beside hard joints usually means cement on a lime wall

We check the brick, the existing mortar and where the damage is before we recommend either, and we trial a small panel so you can approve the colour before we start.

Matching the colour

New mortar always looks brighter for the first few months. We blend sand and lime, or sand and cement, until a cured sample sits with the original joints, and we tool each joint to the same profile. Struck, weathered, flush and tuck-pointed joints all look very different from the street.

What it costs

Repointing is priced per square metre of wall, from about $90 per m² for straightforward work. Heritage walls in lime, high walls that need scaffold and tuck-pointing all take longer, and a good quote will say so.