How do I tell if my pointing has failed?

Mortar joints make up roughly a fifth of the surface of a brick wall and they are almost always more porous than the bricks. When the mortar recedes, each joint becomes a small shelf holding rain against the wall instead of shedding it. On a sheltered elevation that is cosmetic for decades; on the weather elevation of an exposed house it is the difference between a dry wall and a wet one.

What you'll need

• An old screwdriver or a key
• Binoculars
• Torch for raking light (optional)

Step by step

1. Look at the elevation in raking light.Early or late sun across a wall shows recessed joints, cracks and repairs far better than flat midday light. Photograph it then.
2. Scrape a representative joint.Firm pressure with a screwdriver. Sound mortar takes a scratch. Failed mortar comes away as sand and gives you a hole. Test in several places on each elevation — walls are rarely uniform.
3. Measure how far back the joints have gone.Recession of a few millimetres is normal weathering on an old wall. Recession of much more starts holding water, and once the arris of the brick is exposed on its face the brick itself begins to suffer.
4. Look for cracked and hollow joints rather than just missing ones.A hard cement repointing on a soft old wall commonly cracks away from the brick without falling out, leaving a hairline gap that takes in water and holds it. Tap along it and listen for hollowness.
5. Concentrate on the weather elevation.The south-west and west faces in most of the UK. That is where the driving rain lands and where failed joints translate into internal damp.
6. Check the parapets, copings and chimney.The most exposed masonry on the building takes weather from several directions and has no wall above it to shelter it. Joints fail there first and they leak into the roof and the top of the walls.
7. Judge the extent honestly.Spot repointing of a few square metres is a sensible morning's work. If a third of an elevation is failing, patching it will look bad and be back within a few years.
8. Match the mortar to the wall.This decides whether the repointing helps or harms. A soft old lime-built wall needs a lime mortar; putting cement into it makes the brick faces spall instead. Get this right before any joint is cut out.

Tips

• Pointing above first floor level is scaffold or tower work. Repointing from a ladder is one of the classic causes of domestic falls.
• If the wall is stone, or the building is listed or in a conservation area, take advice on the mix and the finish before starting — the wrong mortar on a stone wall is expensive to undo.
• A wall that is losing brick faces has usually already been repointed in cement. That is the diagnosis, not just the damage.

Common mistakes

• Repointing an old wall in a strong cement mix because it will last longer — The mortar joint is meant to be the sacrificial, weaker element so that weathering and movement are taken by the mortar rather than the brick. A joint harder than the brick transfers all of it to the brick face, which spalls off and cannot be replaced.
• Pointing over the existing mortar without cutting out — A thin skim of new mortar over old has nothing to key to. It debonds within a couple of winters and, in the meantime, holds water in the joint behind it.

Questions people ask