how to remove rubble from base of cavity wall?

[maggie73]

My end of terrace whinstone 1870's house is built into a hillside, near the top. The ground floor is completely underground on the northwest side, with a tarmaced road immediately adjacent, and the gable end has a set of public steps running down immediately adjacent. No possibility of lowering ground levels. The house was renovated in the 60's when I assume the cavity brick wall was added on the two walls which are fully/partially underground, and the joists sit on dwarf brick walls on a wooden plinth.
I am experiencing some damp in the corner that is completely underground, some salts are depositing on the internal cement plaster, which seems to attract moisture from cooking etc. joists are good under floor, though ground below is cold/damp to touch in that corner as well, and bricks and wall very cold/damp to touch there also.
having redecorated recently, salts and moisture have damaged wallpaper finish a bit, and will probably have to redecorate in a couple of years, probably replacing cement plaster with lime plaster on those walls. However, I wonder if there is rubble between the solid and cavity walls and causing bridging. (pointing outside on gable end needs redone)How do I investigate this, and if there is rubble, how do i remove it?

 

[Penners]

I'm not arguing with the possibility of damp ingress from outside in some form or another, but your phrase "...from cooking..." could have some significance. I take it that this room is your kitchen?

If so, then condensation shouldn't be ruled out. Yes, there may be some damp in the wall, but condensation could be exacerbating the problem.

If you're not planning to do any redecoration in the room for a couple of years, this gives you a bit of breathing space to do some experiments. If I were you, I think I would first try improving ventilation in the room.

Condensation can be greatly reduced by a combination of warmth and ventilation. Warm air will hold more moisture than cold, and the ventilation will then carry this damp-laden warm air away. I assume that - being a kitchen (if it is!) - the room is already fairly warm. So a well-placed and suitably rated extractor fan could be a good investment at modest cost.

If it has a beneficial effect on the problem, that's great. If not, then an extractor in the kitchen is never a bad idea anyway.

As to the possibility of rubble within the wall cavity, this isn't an easy problem to deal with. Can you gain access to the top of the wall (presumably in your loft) to be able to peer down inside with a torch? If it's a very high wall then you may have trouble being able to see to the bottom, but you could try.

Alternatively, if you're able to do so, try dangling a string with a weight on the end down the cavity, then comparing the length of the string-and-weight with the height of the wall inside the house (remembering that you need to add in the bit below the floorboards, down to the foundation). This latter idea is fraught with problems - string getting caught on cavity ties, errors in establishing wall height, and so on, but it's possibly worth a cautious try.

However... if you are able to establish that there's rubble in the cavity, getting it out could be a considerable problem, short of actually making access holes in the inner or outer wall and hoiking it out through these.

I wonder whether any of the forum's building experts have any better ideas.

 

[maggie73]

the room is actually the livingroom, but the kitchen door leads directly to the livingroom. its a small house and the affected area is only about 3m away from the kitchen door. I have monitored it over the last 6 months or so since i noticed it and when we have periods of dry weather, the area can wet up, but when wet outside, can remain dry. It feels like surface moisture. Undoubtedly we do get condensation in the house, usually only on the sash windows though, and we dont get any mould on the affected wall area, just a very faint tide mark. I read that salts could have risen by capillary action up the wall, deposit on the surface of the plaster/paper and then attract any moisture in the air.
there was no rot on the skirting board when taken off, but some of the plaster immediately above the skirting board crumbled. it is a cold corner, and i just wondered if any rubble was allowing moisture to reach the cavity wall, making it colder and hence attracting condensation? If replastering with lime in a couple of years enables me to manage the moisture i am happy to do that. I was quoted for tanking but having read loads on this site, am not going there.

 

[Penners]

It's interesting that you say there has been no plaster deterioration behind the skirting, but there has above it. To my inexpert mind that seems to support the idea of condensation. If the source of damp was from behind or below the wall, I would expect the area behind the skirting board to be the most severely affected, because it is "stifled" by the skirting. I would also expect the back of the skirting board to be rotting.

You are quite right that any bridging of the cavity could cause the inner wall to be colder than normal, and this would be likely to exacerbate condensation in a warm room.

However, it's impossible to be certain. So I still feel that creating good ventilation in the room is a sensible place to start. But I acknowledge that, as is so often the case with damp problems, you may have to work your way through various solutions before you finally resolve this one.

Anyone else got any thoughts?

 

[maggie73]

thanks for your help. what you say makes sense, that there is some moisture in the wall, being exaberated by condensation.
with regards to the damaged plaster, there was small patches where it fell off behind the skirting as well, but probably aided by the damaged plaster above. the plaster didnt reach the floor: it starts about 3 inches above the floor, with a strip of wood below the bottom of the plaster. this wood was ok as well.
when we moved in about 18 months ago, 'the damp expert' got readings in this corner, and we had the corner replastered with waterproof plaster, above the skirting. i think maybe this waterproof plaster has just pushed the moisture further out of the corner, but interestingly, this new plaster also wets up. its funny how much you learn in a few months, and what a scam the whole damp survey seems to be. If I had known better then, I wouldnt have had the area replastered.

 

[Penners]

The plaster stopping a little above the floor is the correct way to do it.

Yes - waterproof plaster in that corner is undoubtedly a bad thing. You mentioned above that you're planning to remove this and replace it with lime, when you can. Sounds a good plan. But do ventilate too - remember that lime plaster can help dissipate moisture into the air, but you then want to get rid of that moist air.