Damp bedroom wall - no obvious cause!

[Nimster]

Hi all
We have a damp problem in our bedroom. The back wall (with window) is really damp in the top corner, to the extent that the wall feels sticky - almost as if the wallpaper glue/paste has been reactivated by the damp. We've had the paper stripped off for a year, and the wall dried out in summer but following the recent rain, the damp is back with a vengeance. We've been up and looked at the gutters and roof - both are fine. The window is fitted and sealed properly. The room is well-ventilated, so it's not condensation. The only thing we can think is that the sandstone wall has lost it's outer cortex (is that the word?) and is letting water through - the blocks where the damp is are fairly eroded and seem to hold rainwater longer than the surrounding stone.

So, my question is, how on earth do we treat this? Do we seal the outer stonework with [what?] something? We can't think of any other solutions as everything else seems fine. I'm reluctant to paint the interior (once it's dried) with anti-damp paint as that would just force the damp further across the wall past the paint?

Any suggestions?
Many thanks in advance.

Nimster

ps - I tried doing a search but putting in "sealing stonework" brings up thousands of threads and I don't have time to read them all

 

[Nemesis]

Have you checked the pointing?

If it looks at all dodgy try redoing it with lime.

It takes not a lot of a gap to make the water come in.

No it might not help but worth trying!

 

[Matt Green]

It's on an external wall (cold) and in a corner (little air movement). That's sounding a lot like conensation. Is the room heated? If so, how? Is the heat source near the problem?


Matt.

 

[Nemesis]

One problem damp patch we had was actually caused by rain running down a wall at a particular point as the gutter, which looked fine when it was dry, wasn't able to cope in really wet weather. The water soaked through the mortar and found its way inside.

Another tipped backwards and soaked the wall plate...

 

[Gervase]

Aye, penetrating damp is high on the list of suspects. Guttering is a frequent culprit, but sometimes it can be as banal as rain being constantly blown against a wall with defective pointing. Does this wall/corner, face the prevailing wind?

 

[chuckey]

Sandstone can be really porous so it could be a "bad"stone. You say its at a corner? I had a problem with water running down the top of a rock and rubble wall and materializing on the inside some way away from the leak. It has be re-roofed now.
I also had an occurrence where the rain was blowing in from the SW, but due to turberlences an area about 4 feet round the corner on the east wall was totally drenched.
1. check pointing.
2. check stones, wait for a hot day and spray area with water, after 5 minutes a porous stone should still be wet so darker.
3. Spray wall with silicone or wax based stuff
4. ????
Frank

 

[NT]

Coating the wall with waterproof layer is a good way to stop evaporation and thus make things worse.


NT

 

[andrew gayton]

the 'space' between start of roof covering and gutter is a real weak point; water coming off the roof can be wind-driven onto the wall top and soak th ewalling resulting in your problem.......... best to provide a u.v proof membrane to underside of felt and rested in gutter....... especially a problem on clipped or close eaves. my flint place had same problem but had impacted on all of the rear walling (place had been empty for 2 years before i moved in) resulting in green walling - internally! - had to replace 1/2 of th ewallplate as well. membrane has sorted the safe disposal of roofwater though. i agree with mat however that corners do suffer from condensation......... so, get up the ladder and have a look-see.

 

[Nimster]

Thanks all. It's definitely not condensation - the room is heated (GCH) and the window has been open for months to dry out the wall. The problem only reappeared after the recent heavy rain and looks to be coming from the outside in.

The pointing is also fine - OH has been up on there and checked. I suspect it's either the porous stone or a gutter/wind/rain problem. I'll send OH up there next time it's raining to see if he can work out what the problem is. He'll be delighted. We think the gutters may need replacing but it's potentially a £££ problem involving scaffolding and LBC, so fingers crossed there's an obvious, easily fixed, problem.

Thanks again for all the suggestions.
Nimster