Damp on chimney brest

Joined
30 Dec 2012
Messages
222
Reaction score
4
Location
Essex
Country
United Kingdom
I have a 1930 semi, in the lounge we have damp on the chimney breast. The top is capped with a vented cowl. Is the damp coming from the floor? The fire place is not used and has a fake log burner installed. This is an internal wall with the neighbour. I’ve attached an image it is like this on the other side. View attachment 379069
 
Gypsum plaster used where lime plaster should of been used?
That causes damp that's trapped
 
Chimney can get damp though.

Never any damp course under floor there and also condensation from where warm moisture in the air hits cold, you get condensation.

Think you need advice from damp specialist
 
Poster# 2 and #4,
Why would "lime plaster" have been used instead of gypsum - as far as we can see thats not a remedial repair?
Using the term "lime plaster" is also wrong in this context - a mix of "lime render" at 3:1 sand and NH lime is the correct remedial render mix.
 
Last edited:
OP,
Why not post pics of the whole chimney breast?
Does the neighbour have damp issues on the party wall?
Is the floor solid or suspended?
Have you ever had the flue swept?
 
I’ll do some pics of it, floor is solid, neighbour doesn’t have issue. Not had chimney swept as it’s not used. I knocked the breakout out a few years back. Was hoping to sort this summer.
 
Just taken these

IMG_6298.jpeg
IMG_6297.jpeg
IMG_6300.jpeg
 
OP,
Thank you for the pics. Pics of the return wall on the left side of the chimney breast might also have helped?
You need to sweep the chimney flue regardless - people in the 1930's & 1940's & 1950's used solid fuel.
What is the "breakout"?
Does your neighbour have these damp issues?

Its possible that the cause of your rising damp is a soil filled fender wall below where the original concrete hearth was. If you have a suspended floor with an adequate crawl space then any existing fender wall could be examined from below?
Because of the height of the damaged plaster on the LH chimney breast cheek there might also be Hygroscopic chemicals penetrating through the chimney breast brickwork

Why not remove the skirtings on either side of the chimney breast, & hack off to 300mm above & beyond any signs of affected gypsum plaster plus hack sawing off any rusted metal angle bead - replace with a length of plastic angle bead.
You could then hopefully make good with a lime render.
 
The floor is solid, so no crawl space. I’m going to do the room up this summer so will take some plaster etc off to see.
 
It's a fire place. It's 1930's so most likely has had loads of coal fires there over its lifetime. Combustion gases and water down the chimney when the chimney was used, make acids (like acid rain). The acids react with lime based building products and create salt compounds within the bricks and mortar - concentrated around the hearth itself. (just like acid rain and pollution erodes limestone buildings) These salts are hygroscopic and will pull water from the room air and grow crystals.

All the "damp" is most likely coming from the room air (just as it does in our house with the same situation). I have solved this by taking the plaster off, isolating the bricks from the room air first with an SBR slurry and then by overboarding and using foam adhesive (important because water based adhesives will still leach the salts to the surface). Room air can't get to the salts, problem goes away. This isn't theory, it is what I have done in my own house to 100% solve this problem.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Back
Top