Brickwork Repairs and Repointing in South London

These are the jobs too small to interest a builder and too specific for a handyman. If it involves brick, mortar, render or plaster, and it is letting water in or looking wrong, it belongs here.

Mortar is meant to be the weak part of the wall. It takes the movement and the weather so the bricks do not have to. A wall breathes: rain gets into the face and should come back out through the joints, carrying salts with it. That is why old mortar goes crumbly near the top of a wall and under the windows — those parts take the most rain. The joint is doing its job by wearing out.

The damage gets done when someone repoints in a hard sand-and-cement mix. Cement mortar is stronger and far less permeable than a London stock brick. Water still gets in, but it can no longer leave through the joint, so it leaves through the brick face. The first frost turns that trapped water to ice and takes the front off the brick. You end up with crisp new pointing standing proud between a hundred spalled bricks.

So the mix matters more than the neatness. Soft London stocks and anything Victorian usually want a natural hydraulic lime mortar — NHL 2 or NHL 3.5, depending on how exposed the wall is. Harder machine-made brick from the 1930s on is normally fine in a gauged cement, lime and sand mix. Either way the joints get raked back to about two and a half times their width, roughly 20 to 25 mm on a standard joint, with a proper mortar rake and never an angle grinder skidding across soft brick.

Most cracks in a South London house are not structural. Brickwork moves with heat and damp, plaster shrinks, and a settlement crack that opened forty years ago and stopped is just a line in a wall. The useful test is width and behaviour, not how alarming it looks.

Surveyors classify cracks on the BRE's scale. Hairline up to about 1 mm is category 0 or 1 — decoration. Up to 5 mm is category 2, cosmetic damage, and normally a rake-out and repoint. From 5 to 15 mm you are into category 3, where doors and windows start to stick and the repair means cutting out and replacing brickwork. Above 15 mm it stops being a bricklaying job.

So does anything still moving. Diagonal stepped cracking near a corner, a crack that has visibly opened since you first noticed it, or one running through bricks rather than around them can mean subsidence, a failed lintel, or a tree drawing water out of London clay. Those need a structural engineer, and we will not repoint over one — filling a live crack hides the evidence the engineer needs, and it comes straight back through the new mortar.

Render fails from behind. Tap along it with a knuckle: sound render gives a dull thud, failed render rings hollow. That hollow patch has let go of the brick and is holding water against it, so skimming over the top does nothing. We cut back to a solid edge, key the brickwork, mesh across the joint and build the coats back — which is why a render patch takes half a day, not an hour.

Hard sand-and-cement render on a solid nine-inch wall causes the same trouble as hard pointing, for the same reason. It cracks, water gets in behind it, and the render then stops the wall drying out. If a whole elevation is crazed and drumming, patching is money down the drain — that is a strip and start again, a bigger job than this page, and we will say so rather than sell you eight patches.

Inside, plaster that keeps failing is a symptom. Blown plaster low on a wall with a tide mark and white salty bloom is water arriving from somewhere, and re-skimming buries the problem for about a year. Before we replaster we want to know the source — a blocked gutter, a cracked downpipe, ground built up above the damp-proof course, a failed flashing. Fix that, let the wall dry, then make good. That order is not us being difficult; it is the only order that works.

Garden walls fail at the top and the bottom. At the top, a missing or cracked coping lets rain straight into the middle of the wall, where it freezes and pushes the courses apart. At the bottom, most old boundary walls sit on a shallow footing or none at all, and the clay under South London shrinks and swells with the seasons — worse where there is a tree nearby. That is what makes a wall lean rather than crack.

So a leaning wall is rarely fixed by pointing it. Once it has gone past the vertical it needs taking down to a sound course and rebuilding, which is often cheaper than it sounds because the bricks clean up and go back. We will tell you how far down it has to come before we quote, and we will say when only a few courses need to move.

Outbuildings are their own trade. A brick garage or a Victorian coal store usually leaks at the wall-to-roof junction rather than through either one, and that wants lead or a proper flashing detail rather than a tube of mastic. One warning worth having: a garage or shed roof from before 2000 may be asbestos cement. It is safe intact and dangerous broken up, so if we suspect it we stop and it gets tested before anyone touches it.

Half of what we do is roofing, and the two trades overlap constantly. A wet wall on a chimney breast is usually a flashing or flaunching fault, not a pointing fault. A green stain down a rear elevation is a leaking gutter joint. A damp patch under a bay is often the little flat roof above it. If we are already on the roof, the pointing on the stack and the parapet gets looked at on the same visit, because the scaffold is the expensive part and it is already there.

There is work we do not do, and it is worth saying plainly. We do not design structural repairs — anything needing a beam calculation, underpinning or a subsidence claim goes to a structural engineer first, and we work to their drawing or not at all. We do not inject chemical damp-proof courses or sell damp guarantees. We do not remove asbestos. And a full re-render of a house is not a small repair, whatever it is called on the quote.

What we will do is look, tell you which list your job is on, and put a written price on the part we can genuinely fix. If two things on your list are worth doing and two are not, you will hear that.