Chimney wall sweating

[alucard]

HI,
I live in an end terrance house and the upstairs chimney wall is "sweating". I've had builders out to the roof before who resealed the lead flashing, reseated some tiles, repointed the chimney but I still get the problem.

The problem is in one of my bedrooms which has thw chimney on one of the external walls. The ceiling gets a damp patch (but never drips) and the wall fells damp to touch. Been up in the loft and the same wall up their is again damp to touch but no drops running down the call. Looked at the edge where the roof sits on the walls but their doesn't seem to be any water running in.

Anyone got any ideas how I can stop this.
Thanks in Advance
Terry

 

[noseall]

you seem to have a classic case of hygroscopic salts migrating to the surface.

these salts attract moisture from the air and give the impression of damp ingress from an external source and are prevalent within chimney breast masonry.

stripping the plaster from the area, down to the bare brick and treating the brick with an sbr cement slurry will help provide a suitable barrier from the effect of the salts.

 

[alucard]

I'v already done that once, I took all the plaster off in the affected area, painted some damp proof paint (from B&Q i think it was), let that dry, then replasterd.

this only seems to happen when it rains.

 

[mattylad]

You still have a leak.

Are you able to get up there & look yourself?
Could be that the builders did not do as good a job as they said they did.

 

[alucard]

I've been in the loft and cannot see any drips coming from the roof.

I'll be getting some long ladders so I can look then but not for a while. The builders should have capped the chimney and repointed it. But we shall see.

 

[confidentincompetent]

A shot in the dark: Is there a possability of an old aluminium flue being left in the chimney? Does the damp still occur on just cold days? Just a thought

 

[sootylum]

Is the fireplace still in position or has it been taken away and boarded over ?. If it has ensure that a small vent has been fitted where the fire used to be and the chimney pot fitted with a blank cap.
This sounds like one of two things I have come across before, 1. Chimney pot is open and rain is entering the flue running down to the first bend and soaking in through the brickwork. 2. The pot is open and there is a birds nest in the flue which is acting like a sponge absorbing water with the resultant damp patch just at ceiling and wall junction.
Call a chimney sweep out to have a look he/she will be able to help you out. Try the National Association of Chimney Sweeps for one in your area.
Good luck.