Chimney Repairs South Wales › Cardiff › Guide
Damp on a chimney breast worries people because it often appears upstairs, in a bedroom, where the stack passes through. In Cardiff's older terraces and villas, there are several possible causes, and some are simple to put right. This guide runs through them and what we check before recommending anything.
Rain coming down the flue
A cracked pot, missing cowl or worn flaunching at the top lets rain run into the flue and soak the brickwork inside. The water finds its way into the breast, and shows as a patch that gets worse after heavy rain. If the patch darkens after a downpour and fades in dry spells, this is the first thing to suspect.
Condensation and salts
An unused flue with no air moving through it can stay cold and damp, and moisture inside the brickwork carries salts to the plaster surface. Those salts attract moisture from the air and leave a brown, crusty or powdery patch. This kind of damp tends to hang around in all weathers rather than following the rain.
What you can check yourself
Stay inside and on the ground. Note where the patch is, whether it changes after rain and whether there is a musty smell. A loft check from the hatch, with a torch, may show wet brickwork or stained timber near the stack. Please do not climb onto the roof, and do not light a fire in a fireplace that you suspect is damaged.
- Does the patch grow after rain?
- Is it stronger on the upstairs breast than below?
- Is plaster flaking or powdery?
- Any staining on loft timbers near the stack?
What we look at on a visit
We inspect the stack from the roofline, checking pots, cowls and the bed they sit in. We then look at the flue top and the brickwork below, and compare what we find with the pattern of damp inside. If the fault is at the top of the stack, that is where the repair goes. If it appears to be inside, we tell you plainly rather than guessing.
Putting it right
Most rain-related patches are cured by renewing the flaunching, replacing a pot or fitting a cowl. Flashing and repointing have their own pages, so we mention them only where they are plainly involved. Plaster is left to dry out before redecorating. Where the flue is unused, a capped and ventilated arrangement often stops the condensation side of the problem.
- Renew flaunching and secure pots
- Fit a cowl to keep rain out
- Cap and ventilate an unused flue
- Leave the plaster to dry before redecorating
Need a chimney looked at in Cardiff? See chimney repairs in Cardiff, or for the lead and mortar side of it, chimney flashing repairs and chimney repointing and repairs.
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Common Questions
Does a damp chimney breast always mean a roof leak?
No. Rain through the stack is one cause, but condensation in an unused flue and salts in old brickwork are also common. We check the top of the stack and the pattern of damp inside before telling you which it is likely to be.
Can I just repaint over the patch?
It will probably come back, and salts can push the paint off. Find and fix the source first, then let the wall dry before redecorating. Painting over damp only hides it for a while.
Is it safe to use the fireplace with a damp breast?
We would not use it until the cause is found. A damaged flue or stack can be unsafe. Get the chimney looked at first, and use a qualified person for any appliance or flue question.
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