Spalling brickwork

Why are my chimney bricks crumbling or spalling?

When the face of a brick flakes away, it tells you something about the stack. Here is what spalling is, what the survey traces, and what the repair involves.

The short answer

Spalling is the face of a brick flaking or breaking away, and on a chimney it points to wet brickwork, so the repair starts with finding where the wet comes from. A few damaged bricks can be cut out and replaced with the pointing renewed. Where whole faces are going, the top of the stack may need rebuilding.

4 min read · Part of Chimney repairs

Lead flashing stepped up the side of a brick chimney on a clay-tiled roof — Flaking brick faces near the top of a stack

What spalling looks like on a stack

A spalled brick has lost its hard outer skin. The face comes away in flakes or small plates, and what is left underneath is softer, rougher and sometimes a different colour. On a chimney you may be able to see it from the garden, and the flakes can turn up in the garden, a downpipe hopper or a porch roof below.

Crumbling is not always spalling, so the survey separates the cases.

Signs on the brickwork and what we note
What you see	What we note
Brick faces flaking off in plates	Spalling: how far down each brick it runs
Sandy dust coming off the mortar	Pointing past its best, which is a mortar fault
White powder on the surface	Moisture in the brick: noted with the search for where it enters
Cracks running through bricks	Movement: a separate check on the stack

Keep a few of the flakes in a bag and photograph the worst bricks, with a coin or a tape beside them for scale. They show the surveyor how deep the loss goes, and whether the bricks are soft all the way through or only at the face. Do not scrape at them or pull loose pieces away yourself from a ladder.

Tracing where the wet comes from

A stack stands in the open on every side, so its brickwork takes whatever the weather brings. Spalling tells you the bricks are getting wet and staying wet, and the survey looks for the reason, because new bricks set in the same conditions would suffer in the same way, and the repair would not last.

From the roof, the survey looks at:

the pointing between the bricks, for open or crumbling joints
the flaunching, the sloping mortar round the pot, for cracks that let water down into the stack
the lead where the stack meets the slope, for lifted edges or gaps
the pots and any cowl, for cracks or missing pieces
the cap or top courses, for loose or missing bricks

Inside the house, damp on the chimney breast or a stain on the ceiling beneath points to the same cause. A stain from the room side is traced separately from the roof. Spalling that sits only on one face may mean the weather arrives from one side, and the survey notes the direction.

Replace the bricks, repoint, or rebuild the top

The survey sets out which route the stack needs, and none is chosen before we have looked at the brickwork close up, from the roof, with a camera.

Brickwork condition and the repair route
Condition of the stack	Work it leads to
A few bricks spalled, the rest sound	Cut out and replace those bricks, then repoint
Pointing failed across the stack	Repoint the stack, with spalled bricks replaced
Top courses crumbling right through	Rebuild the top of the stack
Bricks failing the full height	Rebuild the stack from the roofline

Painting or coating a spalled brick does not give it its face back, and it can hide the problem from the next inspection, so the cause is dealt with before the finish. A repair that skips the cause can look right at first and then fail again. New bricks are chosen to match the old ones in size, colour and texture as closely as the supply allows. Our guides on chimney repointing and stack rebuilds explain the two bigger routes.

Listed homes, access and the written price

On a listed home, consent is required for any work that alters its character, and swapping a brick for a different one can do that, so the council is asked before bricks are matched or replaced, and the answer is kept with your papers. Altering or replacing a chimney is outside the permitted development rule for roof alterations, Class C, and a conservation area can add an Article 4 direction. Ask the council before any brick is changed on a listed home or one in a conservation area, and send it the survey photographs so that it can see what is meant.

Brickwork at the head of a stack is worked on from scaffold or an equivalent platform. Scaffold that overhangs the highway is licensed by the county, and we arrange the licence with our scaffolder. Our page on scaffolding for chimney repairs gives the fees and periods for Kent and East Sussex.

You get one written total price after the survey, with the scaffold in it, and it states whether bricks are to be replaced singly or the top rebuilt. Everything we do on stacks starts from the chimney repairs page.