Damp/condensation on chimney breast

asxx

I live in a mid terraced house and have damp / condensation problems on the chimney breast in the upstairs room at the back of the house. The problem does not appear after rain but when the relative humidity of the atmosphere is high and it is dependant on the weather. When the relative humidity of the outside atmosphere is high we notice the problem.

I think that it is condensation of moisture onto the plaster which is possibly contaminated with hygroscopic salts. The wall above the fireplace is soaking wet under certain conditions but then when the relative humidity drops it dries out fairly quickly. The plaster also has a mottled appearance.

Could anyone give me some advice on how to rectify this?

dampdaveski

Hi asxx,
It does indeed sound like hygroscopic salt contamination of the plaster, probably sulphates from when there was a coal fire.
Assuming you've discounted lead flashings / roof problems
You probably need to strip the plaster off and install a cavity membrane with mesh on it, then plaster on top of it
http://filesdown.esecure.co.uk/wykamol/5._Kontract_Mesh.pdf_05102009-1713-10.pdf
This is off the wykamol website, but you can get this type of membrane from loads of places, you just need to do a bit of research for the cheapest.
If the problem isn't too bad you could try painting a stain blocker on, though this might not be very effective.
Alternatively try a contractor who is a PCA member www.property-care.org they are used to dealing with this kind of problem

hope this helps
DD

asxx

Hi dampdaveski,

Thanks for the advice. I'll get a few quotes from local contractors on the link you sent. Do you have any ideas on how much it is likely to cost? - the affected area is about 110cm wide and the floor to ceiling height is about 250cm which includes the fireplace.

Thanks

asxx

dampdaveski

Hi asxx,
always difficult without seeing it, and it might be worth doing both of the sides too, but I imagine it will be around the £400-£600 mark depending on where you are in the country, could be a lot less, but shouldn't be any more
hope this helps
DD

MX5huggy

Are you using the chimney?

asxx

Hi MX5huggy,

No the chimney is not in use.

Mr_Warren_2

Is the chimney blanked off and the exit flue on the roof capped?

asxx

Hi Mr Warren,

From looking at the chimney from ground level it is capped with what looks like an insert for venting the chimney.


asxx

asxx

Hi Mr Warren,

and the chimney has the original Victorian fireplace with a vent that can be opened or closed.

Mr_Warren_2

It could well be that as your chimney duct is not vented enough and condensation inside is ripe, droplets depositing on the inside of the brick work and penetrating into the room onto your plaster wall.

You could get the top exit re-opened in order to allow a greater flow of air that would allow your plaster to dry.

dampdaveski

Mr_Warren wrote: »

It could well be that as your chimney duct is not vented enough and condensation inside is ripe, droplets depositing on the inside of the brick work and penetrating into the room onto your plaster wall.

You could get the top exit re-opened in order to allow a greater flow of air that would allow your plaster to dry.

It's not a bad idea at all to get the 'stack' reopened, however the plaster is now contaminated with sulphate salts, during decent weather the patches will shrink or even disappear, but as soon as it rains or the humidity levels (ie condensation in the room) rise it is likely they will reappear with annoying regularity.
DD