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Damp Proofing

Damp in chimney breast

I live in the ground-floor flat in a Victorian terraced house. I've got a problem with damp on a chimney breast in my kitchen. The chimney breast is actually in two rooms – the corner of it is in the bathroom. There's a stud partition wall separating the bathroom and kitchen. In front of the chimney in the kitchen are some units and a sink.

• The chimney hasn't been used for over 40 years.
• It's been removed in the upstairs flat so doesn't go all the way up to our roof. (The roof is in poor condition.)
• The wall where the chimney is backs onto the terrace next door.

I first noticed the damp creeping along the wall in the bathroom. The plaster on the chimney breast behind the kitchen sink next door also felt damp.

At first I thought it was the result of occasional spillages from the sink or the waste plumping, so:

• I used silicon seal around the worktop.
• Made sure all the waste plumbing was sealed. The waste pipe was leaking but I fixed it.
• I had a damp-proofing contractor look at the damp area in the bathroom.
• He hacked off the plaster, coated the chimney breast with slurry and replastered.

It seemed to get better in the bathroom although the plaster behind the sink still seemed a bit damp.

Recently I noticed a damp patch creeping along the partition wall in the kitchen. I thought it might be to do with old pipes that feed the kitchen sink, which were sunk into the concrete. All of the water pipes that serve the kitchen and bathroom had been run through concrete and looked corroded.

• I cut off the water pipes and blew the water out using a rubber tube. (One of the pipes definitely started weeping when I gave it a tug before cutting it off. I don't know if it was already leaking water.)
• I laid new pipes on the surface, threading them behind the kitchen cupboards.

I wanted to replace my kitchen tiles anyway, so I pulled them off the chimney breast above the worktop/sink. The wall underneath was very damp. Since I'd only recently cut off the old pipes, I still thought they might be the cause. So I thought I'd leave the plaster to dry out. That was about two months ago and it's no better now. The patch of damp forms a big semicircle behind the kitchen sink and on the adjacent wall to a height of about 1.5m.

I've checked the pipework around the sink and it seems dry. The waste pipe runs through a hole in the chimney breast, then takes a 90 degree turn and exits the chimney breast in the bathroom. But that feels dry too.

The whole area is very difficult to access because it means getting inside the cupboards under the sink and groping around to get to the plumbing, both behind the unit and inside the chimney breast behind that.

Do I need to remove the sink and units, then get the plaster hacked off and have the chimney breast treated and replastered? Could the problem still be the roof, even though the chimney breast has been removed upstairs?

Any advice would be gratefully received!

6 Answers from MyBuilder Damp Proofing Specialists

Best Answer

Everybody is missing the most common damp problem in chimneys that are out of use and removing them doesn’t help!
Burning coal in oxygen creates I salt called ammonium sulphate, this contaminates the flue ; it’s hygroscopic which means it absorbs moisture from the atmosphere.
There are solutions to this and they’re not dramatic or expensive.


Answered 1st Sep 2019

Ok forget rising damp that doesn't exist.
You must have a leak somewhere. Locate and fix the leak, vent the stack somewhere to get some air into it, let it dry. Repair. Covering this problem with tanking slurry and silicone will not work.
Had a very similar situation with a broken sink waste that was filling a cavity wall every time the sink was emptied (making my own indoor paddling pool!). Wasn't until I demolished the wall 2 years later that the problem was found. A bit of a drastic measure but not even the architect knew what the issue was.


Answered 19th Jun 2019

Make sure any leaks are fixed out of use chimneys are dreadful for creating damp ignore anybody saying rising damp. It doesn't exist.condensation is by far the culprit. if you're replacing any plaster make sure it's replaced with lime mortar Victorian buildings don't sit well with cement and modern plaster get ventilation up graded drafty is better than damp , don't pay any attention to a surveyor with a damp meter trust me he is not qualified to comment good luck and open that window


Answered 5th Jan 2021


Thanks for the post. My initial start point is always from the chimney pots and then work my way down the building (Ridge, Roof, gutters, Walls, Damp Proof Course). If the issue stems from the roof then the floor above should also have the same issue and a good indication that attention is required above this floor. Although the chimney has been taken out in the floor above, has it been properly capped off at chimney level? If not then then this is a good place to start as well as inspecting the chimney stack, ridge, general condition of the roof etc. If the damp is rising through the floor then there is a limitation of 1.3m in height for capillary action from a failed Damp Proof Course. If the damp is a lot higher than 1.3 m then my guess is the water is coming down and not rising up

I hope this may give you a couple of pointers



Answered 8th Feb 2016

Have you got vents in it? When the above was taken down did they backfill yours? That would cause an issue.


Answered 2nd Jan 2020

It smacks of a condensation problem to me. Warm air from all around a possibly cold air ,un vented void in the middle. You would be amazed how much moisture that can create. Please get a surveyor in to map out the remedial works needed and get a reputable builder to do it. The surveyor should be able to help you with that. Hope it goes well.


Answered 9th May 2020

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