Why has my new pointing crumbled or fallen out?
Seven reasons fresh pointing fails within a year or two, how to tell them apart from the way it failed, and what has to be done differently on the second attempt.
- Difficulty
- intermediate
- Time
- 25 min
- Read
- 4 min
Short answer
Nearly always one of: not raked out deep enough, the joint was dusty or dry when filled, the mix was too dry or too wet, it was not compacted into the joint, it dried too fast, or it froze. Scrape the failed area — if the mortar is thin and the old surface behind it is smooth, the depth was the problem, which is the commonest cause by far.
Pointing that fails quickly is demoralising and it is almost always a preparation failure rather than a materials one. New mortar needs three things to stay in a joint: enough depth to have some mechanical grip, a clean damp surface to bond to, and enough moisture retained long enough to hydrate. Take away any one and it drops out, usually after the first winter.
Step by step
- Establish how deep the failed mortar went.Pull some out and measure it. Anything under about 10mm was never going to stay in. The joint should have been raked back to at least twice its width.
- Look at the surface it was sitting on.A smooth, dusty, unraked surface behind the failed mortar tells you immediately what happened. A square, clean, freshly cut recess means the depth was right and something else went wrong.
- Check what mortar the wall wants.Before redoing it, establish whether the wall is lime or cement. Repointing an old soft-brick wall in cement will fail again, and it will damage the bricks in the process.
- Rake out properly this time.To at least twice the joint width, square, with clean vertical arrises against the bricks. Use a plugging chisel and a lump hammer by hand rather than a grinder, which cuts brick arrises as easily as mortar.
- Brush and dampen before filling.Brush every joint out with a stiff brush, then wet the brickwork thoroughly and let the surface water go. A dry absorbent brick sucks the water straight out of the mortar and the mortar never hydrates.
- Mix pointing mortar stiff.Considerably drier than mortar for laying — it should hold together when squeezed and not slump on the hawk. A wet pointing mix shrinks and stains the brick face.
- Fill in layers and compress each one.For a deep joint, fill in two or three passes, pressing each hard into the back of the joint with a pointing iron and letting it stiffen before the next. This is what makes the joint solid rather than a shell.
- Tool at thumbprint firmness.Wait until the mortar takes a print and holds it, then tool the profile firmly to compress the surface. This closes the pores and is a large part of what makes a joint weather-resistant.
- Protect it while it cures.Damp hessian under polythene, held clear of the face on battens, for several days on a cement mortar and weeks on lime. Keep it out of direct sun, wind, heavy rain and any frost.
- Work in the right season.Mild, damp, still and frost-free. Not a hot July afternoon in full sun, and not October if you are working in lime.
If it doesn't work
The new mortar comes out as a thin flake, and the joint behind it is smooth
Cause: Not raked out deeply enough — the mortar had no thickness and nothing to grip — Fix: Rake out to at least twice the joint width, square, and refill in layers. This is the commonest cause of failed pointing and it cannot be corrected without redoing the work.
It crumbles to sand between the fingers
Cause: Too little cement or binder, or the mix dried out before it could hydrate — Fix: Rake out, gauge the mix strictly by bucket, dampen the joints before filling, and protect the work for several days after.
It is hard but has shrunk away from the brick on both sides
Cause: Too wet a mix, so it shrank as it dried, or the joint was dry and sucked the water out of the mortar instantly — Fix: Mix stiffer — pointing mortar should be much drier than laying mortar — and dampen the brickwork before filling so it does not rob the mix.
It fell out after a hard frost, in patches
Cause: The mortar froze before it had gained strength — Fix: Redo in the right season. Cement pointing should not go on if a frost is forecast within the first days; lime pointing needs weeks of frost-free weather.
It failed only on one elevation
Cause: That elevation takes the weather, or it was in full sun and dried too fast while the others did not — Fix: Protect while curing — damp hessian under polythene held clear on battens — and work in the shade, following the sun round the building.
It looks dense but sounds hollow when tapped
Cause: Pressed in but never compacted, so there are voids behind the face — Fix: Fill in layers, pressing each one hard into the joint with a pointing iron before adding the next. Do not fill a deep joint in a single push.
Hard cement pointing on an old soft-brick wall is coming off in sheets
Cause: The mortar is stronger than the brick, so it has failed at the interface and taken brick face with it — Fix: Remove the cement carefully, by hand, and repoint in lime. This is not a workmanship failure but a materials mismatch, and forcing it will damage the wall further.