Drawing of a brick wall in stretcher bond with hatched cut bricks at the ends and setting-out lines — Stretcher bond set out, with the cut bricks at each end hatched and the setting-out lines marked through the middle.

Repointing a short run of brickwork

18 June 2009 · album: Yard and Porch · permalink

Raking out is most of the work, and the depth it is raked to decides whether the repair lasts.

New mortar pressed into a shallow scrape has almost no key and falls out within a season or two. The rule of thumb is to rake back to roughly twice the joint width, so the new material has depth to grip, and to rake square rather than to a feathered edge.

Do it with hand tools on a small run. Power tools cut fast and cut the brick arrises just as fast, and a wall with nibbled brick edges looks worse repointed than it did decayed. A plugging chisel and patience beat a grinder on anything under a few square metres.

Brush the joints out and damp them down before filling. Dry brick pulls water out of fresh mortar so quickly that the mix never hydrates properly, which produces a joint that looks right and crumbles under a thumbnail a month later.

Mix softer than the brick, not harder. A hard cement-rich mortar in a soft old wall moves the stress into the brick faces, and the faces spall off instead of the joint wearing. This is the single most common and most damaging mistake in repointing older brickwork.

Fill in layers on deep joints, letting each firm up before the next. A single deep fill shrinks unevenly and cracks along its length. Two passes take a few minutes longer and behave properly.

Finish when the mortar has gone from wet to what is often described as thumbprint-firm. Too early and the tool drags the mix out; too late and the surface will not compact, leaving a rough joint that holds water.

Match the existing profile rather than choosing a favourite. A weathered joint on a wall of flush joints, or the reverse, marks the repair out from across the street even when the colour is a perfect match.