Cutting Out and Replacing Spalled Bricks in a Stack

When single-brick replacement is the right repair

Cutting out individual bricks suits a stack that is sound overall but has a few faces that have spalled badly. It keeps as much original masonry as possible, avoids the disruption of a rebuild, and leaves the stack looking like itself. The condition is that the surrounding brickwork is strong enough to carry the load while a brick is out of it. That is a judgement made on the spot, brick by brick, and it is why a quotation for this work rests on a close look rather than a count from the ground.

It is the right answer when the damage is scattered or confined to a few courses. It is the wrong one when most bricks on a face have lost their skins, when whole courses are soft, or when the stack is leaning or cracked through. Replacing a dozen bricks in a stack where the rest are about to follow is money spent on a patchwork. The comparison between patching and rebuilding is set out in Repoint, Rebuild or Remove? How the Decision Gets Made.

Position counts as well. A brick low in a stack, with plenty of sound masonry above and around it, is a far easier candidate than one in the top courses, where there is little weight holding things together and the head may already be loose. Bricks right under the projecting courses at the top are often best dealt with as part of a larger repair to the head, not as isolated replacements.

Choosing a brick that will live alongside the old ones

Colour is the part everybody notices, but it is not the most important. A replacement that is much harder or denser than the old bricks will take in very little water, which sounds good but pushes the moisture and salt into the softer bricks around it, so the neighbours decay faster. A replacement that is much softer will fail first itself. The aim is a brick of similar size, similar absorbency and similar strength to the ones around it, and that is usually found among reclaimed bricks of the same period rather than modern ones.

Size matters for the courses. Older bricks vary a little and are often slightly smaller than modern standard sizes, so a new brick can leave the bed joints too thick or thin and break the line of the courses. Texture and the face of the brick also differ between machine-made and hand-made types. Expect to look at samples against the existing stack in daylight, and expect that a perfect match is not always available. On a coastal stack such as those covered for chimney repairs in Hoylake, where the pressed red brick is a feature of the street, we would sooner say so plainly than pretend.

How a brick comes out

The old pointing around the brick is raked out first, using hand tools or a carefully controlled cutter, keeping clear of the arrises of the bricks that are staying. The aim is to free the brick without shaking its neighbours. Where it is bonded firmly, it is broken out in small pieces rather than levered, because pulling against a sound joint can crack the brick next to it. Dust and debris are cleared from the hole, and the surfaces on all sides are inspected, since they show whether the surrounding bricks are fit to stay.

Order matters. In a stack that is taking load from above, bricks are generally removed one at a time and replaced before the next comes out, rather than opening several holes in the same course. At the very top, the work is planned so that the head is never left without support. Anything that looks unsound on inspection is raised there and then, rather than closed over.

Bedding the new brick and bonding it in

The new brick is dampened so that it does not pull the water out of the mortar, bedded on a full bed and buttered on its sides, then pressed into place so that mortar is squeezed out evenly from all joints. The bond pattern is kept exactly as it was, with headers and stretchers where they were, because a brick laid the wrong way in a bonded stack is a weakness as well as an eyesore. The mortar is mixed to suit the old bricks, not to be as strong as possible, and the reasoning is the same as in our guide to Repointing a Chimney: Why the Mortar Mix Matters More Than the Finish.

Joints are finished to match the profile around them, and the work is protected while it cures: out of rain, out of drying winds and away from frost. On an exposed frontage that protection is a real part of the job, and a spell of poor weather means the work waits.

Once the new bricks are in, the surrounding joints are checked and any that have been disturbed are repointed so that the repair does not leave a trail of open joints around it. That final pass is what makes the stack watertight again, and it is the part most easily skipped by someone in a hurry. You should not see mortar smeared across the faces or bricks sitting proud of the line of the wall.

Turning a brick, and the limits of the method

Sometimes a spalled brick is sound at the back. Where it is, it can occasionally be taken out, reversed and set back with its good face outwards. It saves a match problem, but only works when the brick is thick enough and the back is clean and undamaged, and an old brick that has been salt-laden through its whole body will simply spall on the other side. It is something to be judged brick by brick, not promised in advance.

There are limits beyond that. Replacing individual bricks cannot cure a stack that is damp throughout, wrongly pointed, or failing at the head. If the cause is water getting in from above, the cause must be dealt with first, and our guide to What Should Be on a Chimney Repair Quotation? lists what a sensible written quotation should say on this. Roofline Solutions is fully insured, gives free written quotations, and will tell you if a stack is past patching.