Penetrating Damp - don't know where to start

[bobblehat]

Hi,

I'd really like some advice please.

We have a top bedroom that has a damp patch on the gable wall. When the weather has been dry for a while, it patch is lighter and seems less obvious. The wall is papered.

The patch takes the shape of the chimney and is in the right place for it to be exactly over the chimney (the fireplace in that room has been taken out however there is still a fireplace in the downstairs lounge - that this chimney is connected to).

Although the house is victorian, the affected gable wall was rebuilt (about 15 yrs ago) when the rest of the terrace was knocked down and a cavity wall was created. This has not been insulated.

We had the roof redone about 3 years ago thinking that the problem was stemming from there. This hasn't altered it.

We also painted over the paper with numerous coats of undercoat before decorating and this kept the stain away for about 1 month.

We had the chimney swept as someone suggested that soot might be holding moisture against the wall but that didn't change anything. The chimney sweep did suggest creating a hatch for the purpose of sweeping the chimney in the affected room (so he could do a better job). We haven't done this yet.

People have suggested re-plastering, but I want to know how to stop the moisture problem before we do this.

Any suggestions?

Many thanks

 

[fidom]

Is the chimney pot open to the elements? If so you should fit a "Chinese Hat" over it. This will also stop any birds falling down the chimney.
http://www.screwfix.com/p/chimney-birdguard-aluminium-stainless-steel-240-x-310mm/50130

 

[bobblehat]

Good questions as I didn't mention this,
there isn't a chimney pot anymore, when the roof was re-done we got them to take it down and slate over the area.

 

[JohnD]

chimneys will suffer internal condensation unless they are ventilated top and bottom. Many chimneys contain an upstairs and a downstairs flue and both must be ventilated. An airbrick or similar is adequate. It is condensation, not penetrating damp.

 

[bobblehat]

Thanks John, we will give that a try.

Once this is done would you recommend painting over the damp mark again with undercoat or will we need to get new plaster?

Thanks

 

[JohnD]

when it is dry, take the paper off and see if there is a yellow or brown stain from the chimney tar.

Tar comes through most things, though you can get a special sealer.

 

[bobblehat]

Great, thanks very much John