New member - apologies, but another post about damp

[rubble2]

I have just joined the forum and have read the Damp FAQ section but I wondered if anyone could shed any light on the particular problem we are experiencing?

Our property is a semi detached house built about 1914 - Solid walls, wooden floors. The front wall is rendered and painted, we have a problem with damp under the window on the front downstairs bay. The bay is contructed of wooden window frames set into sandstone mullions and a stone cill. The damp appears directly under the window frame in one of the front corners of the bay and extends about 3 or 4 feet along the bay and down to a maximum of 9-12 inches down the wall. The damp is most apparant 2 or 3 days after rainfall and fades after a reasonable dry spell. I have checked the render and the condition of the window frames, all seems good. I have resealed the joint between the window frame and the cill with sealent but the damp persists. Another factor which may be relevant is that a number of weeks after painting the stone mullions and cill (good qulaity masonary paint) brown stains appear at random points on the stonework as if caused by damp in the stone, is it possible for the stone to become porous despite being painted? and does anyone know the best way forward to resolve this problem please?

Thanks

Roger

 

[Pford75]

Welcome to the forum. Hopefully some of the resident damp experts will be along shortly....but in the meantime here are my amateur ramblings.

1. What is the wall rendered with? Is it cement or lime? Is it painted also? How recently was all the painting done? The reason I ask is that if the cill/wall etc have been painted recently, it could be that moisture is no longer able to evaporate readily outwards from the wall and now comes inside

2. If the cill has recently been painted, is there a possibility of water 'tracking' back underneath the cill? Some wooden cills have drip grooves to prevent this happening....perhaps a coat of paint on the cill has made it easier for water to track back towards the wall (hence why you get damp underneath the window)

3. What is the ground covered with outside the window? Is there a possibility of splash-back from rainfall?

4. Finally, I'm sure others may suggest this also...masonry paint is not breathable and can trap moisture inside the wall. A better option would have been limewash.

 

[DaveBrigg]

Hi and Welcome
A bit difficult to diagnose without seeing it, but it sounds like you have got a pretty good idea i.e. it is caused by rain getting through the render, possibly at a joint with the cill. Be aware that damp can travel through walls in any direction, so the source may not be where the most obvious damp patch appears. In an earlier house we had dampo in the same place because the air brick in the window bay was blocked. In your case, try looking at the underside of the cill. There should be a groove to stop the water running off and along the underneath of the cill. As a last resort, try testing this with a watering can to see where the water runs.

Beaten by Pford! I think his point 2 is what I was trying to say.

 

[rubble2]

Thanks for the responses, The cill is stone but it does have a grip groove (not particularly well defined in places) I have considered taking an angle grinder to the underside of the cill in order to recut the groove but haven't worked up the courage yet. There is a lot of build up of old paint on the cill, anyone any suggestions as to the best way of removing masonry paint? would ordinary paint stripper be effective or would it attack the stone? Take onboard the suggestion about lime wash but the masonry paint was already on the house when we bought it.

 

[Feltwell]

Have a look at this website, they sell products to strip pretty much anything from anything and are very highly rated - just don't bother with Klingstrip on softwood!

http://www.stripperspaintremovers.com/

 

[Lime]

If the damp patch is appearing directly under the sill it has to be water running back to the wall somehow.
If the drip edge is vague in places it may be running back there.
On the otherhand you need to look at the sill when it is raining to see exactly what is happening.
almost certainly water will run to the damp end of the sill and run/trickle/soak on to the wall somehow.
I don't think any sort of masonary paint can stop water penetration at junctions and joins particularly under the sill.
Once water is behind the paint it will direct and hold the water in the wall and down.
The slow appearance of the damp after rain is probably the slow penetration of water through and into the paint as a whole.
The wall will be wet behind it before it shows through.
Same with the damp random patches elsewhere, probably caused by small holes in the paint.

 

[rubble2]

Thanks everyone for the useful suggestions, plenty to try so I will press on and let you know when (if) I get the problem resolved