Porous masonry / damp diagnosis

[jajaja393939]

Hello all, and Merry Christmas

Need some help please diagnosing damp problem. Damp patch is where wall mee= ts ceiling in ground floor room, and gets worse after rain. Room above has no sign of damp, but does have window directly above problem= spot. The house is victorian and the window looks ok, but the ledge is mas= onry, one lump of I think sandstone. This masonry is a bit like sodden oasi= s to touch but not crumbly or cracked, and does not slope away from the hou= se as i suppose it should.

My theory is that the masonry has become porous, collects plenty of water (= south west facing), which reappears as a problem patch downstairs. Can masonry really be that porous?

Am thinking of sealing with some kind of silicone sealant wash - any advice= out there please

Much obliged

[The Medway Handyman]

ceiling in ground floor room, and gets worse after rain.

spot. The house is victorian and the window looks ok, but the ledge is masonry, one lump of I think sandstone. This masonry is a bit like sodden oasis to touch but not crumbly or cracked, and does not slope away from the house as i suppose it should.

(south west facing), which reappears as a problem patch downstairs.

out there please

Worth trying a couple of coats of Thompson's Water Seal

[Brian Gaff]

Some years ago I had something similar, turned out that the wallcote material on the wall had been breached by some work I'd had done on an upstairs window and the damp got behind the coating, blew the render and got in that way. Once I had the stuff fixed and rerendered and coated the issue went away. Of course this hous has single walls, no cavity.

Brian

[stuart noble]

Two part wood hardener (aka polyester resin) is quite good for sealing sandstone. You really do need dry weather though

[harry]

eets ceiling in ground floor room, and gets worse after rain.

em spot. The house is victorian and the window looks ok, but the ledge is m= asonry, one lump of I think sandstone. This masonry is a bit like sodden oa= sis to touch but not crumbly or cracked, and does not slope away from the h= ouse as i suppose it should.

(south west facing), which reappears as a problem patch downstairs.

ce out there please

Yes it can. But bad pointing can cause this too. Even hairline cracks in the pointing. If so it will need repointing.

You need to find out if you have cavity walls or not.

Also check round the window frame above that the sealant is intact. This is quite a likely one.

Sometimes these water repellent washes work, sometimes not. If there are cracks, they won't work. The problem with the silicon ones is that if it fails to work the next solution is cement render or masonry paint which adheres poorly to the walls when they have been siliconed.

[Dave Liquorice]

I wouldn't any moisture in the stone will be trapped and at this time of year likely to freeze...

As others have said check the pointing don't forget under the cill projection, does the cill have a drip groove? Is it clear of full of spiders web? Check the window frame seal (all the way round).

Is there a radiator or other pipe work near the damp patch, though as you say it gets worse with rain. How long after?

[meow2222]

eets ceiling in ground floor room, and gets worse after rain.

em spot. The house is victorian and the window looks ok, but the ledge is m= asonry, one lump of I think sandstone. This masonry is a bit like sodden oa= sis to touch but not crumbly or cracked, and does not slope away from the h= ouse as i suppose it should.

(south west facing), which reappears as a problem patch downstairs.

ce out there please

Sandstone is inherently porous. A flat porous surface sounds like faulty de= sign, but I know some are that way. Since they're going to let water into t= he wall, you need maximum bare evaporation area and a cavity wall to handle= that. Another approach is to paint the top and sides but leave the undersi= de bare. Another is to put a slope on the stone top.

NT

[stuart noble]

+1

[stuart noble]

Good luck with that, as they say

[harry]

Can be done with an angle grinder on say the cill if the slope is the wrong way.

[jajaja393939]

Thanks, this is the bit that bothers me, the lack of slope, I'm now thinking it might never really get fixed until that gets sorted - somehow.

Thanks a lot for responses, to reply to some of the other points:

The thompson water seal - can anyone advise - i can't work out whether it is designed to be impermeable therefore not breathable or whether it does breathe. The can doesn't say.

[harry]

ing it might never really get fixed until that gets sorted - somehow.

is designed to be impermeable therefore not breathable or whether it does = breathe. The can doesn't say.

Dunno. But I have used it successfully in the past

A couple of other points.

Check the gutter is clear/not overflowing in rain and not leaking.

Check there are no missing/broken roof slate/tiles above where the leak is. You may need to give them a tug, the break may be concealed.

[meow2222]

Are you suggesting stonemasons are less than reliable?

NT

[stuart noble]

I've done this a few times over the years with varying success. You need something that sets reliably in very thin layers and can be "feathered" at the edges. Two pack latex floor screed would do it but AFAIK only comes in 25 kgs. SBR mixed with cement is almost as good. I might also try the new type of ready mixed fillers in tubs, which are very far removed from the traditional Polyfilla type of product. Their main advantage is speed of setting, which may well, be a benefit in this case. Then of course there's car body filler, which is very fast setting but not easy to apply as a skim coat.

[The Medway Handyman]

it might never really get fixed until that gets sorted - somehow.

designed to be impermeable therefore not breathable or whether it does breathe. The can doesn't say.

It breathes.

[stuart noble]

+1 AIUI it, it doesn't form a film, but is more like groups of molecules. Rather like the stuff they inject I imagine