Mould, condensation & efflorescence on a single skin wall.

Hi,
I have a problem with mould on a single skin wall in a bedroom.
It's a 1930's 3-bed semi with bay windows. Downstairs, in common with the rest of the house, the lower part of the bay is cavity-wall brickwork.
The problem is that upstairs, in the front bedroom, the lower part of the bay is actually a 4-panel single-skin affair. Limited investigation show that it's a wooden framework filled with a mixture of broken brick and mortar, pebbledash-rendered on the outside and plastered on the inside.
The inside surface of this bay gets quickly covered with large patches of black mould. In winter, the surface is visibly damp.
I initially sealed the outside with waterproofer (Thompson's Rainseal or similar) to ensure that no water was coming through from the outside and then covered the inside with a double layer of 2mm polystyrene sheeting to try prevent condensation.
Alas, in a few months, the PVA glue failed and the sheeting peeled away from the wall because it was being lifted off by efflorescence. And, of course, it is all now covered in mould again. :(
Is it possible to /ever/ treat a wall like this to prevent mould occurring or should I simply do what I suspect is the 'proper thing' and erect some kind of inner skin to turn it into a cavity wall?
If I do have to turn it into a cavity wall, what's the best material (and method) to use?
TIA
--
-blj-

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On Sat, 17 Feb 2007 08:40:28 +0000, Brian L Johnson wrote:

===================================It depends on how much work you're prepared to do and the general condition of the bay. If the outer skin is in reasonable condition then the best thing to do is to remove the inner skin, (lath and plaster??) clear out all the rubble, assuming that it's loose enough to remove. Having done this then a membrane can be fitted and the void left by the removed rubble can be filled with insulation. Complete the job with flexible plasterboard.
Before doing any of the above check the state of the 'mixture of broken brick and mortar' infill. It's possible that this is intended to be there as some kind of supporting wall or it may just be builder's rubble. Check to see if it's loose enough to remove by hand or whether it's intentionally mortared together.
Cic.
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Cicero wrote
<snip>

It looks awful. I'll end up doing quite a bit to it, I think. :)

I've had a dig around in one corner. <g>
The outer rendering looks to be in good condition (and, as I said, I've liberally doused it in waterproofing liquid -- whether or not it's effective is anybody's guess) with no pinholes or cracks.
The bay wall itself is made up of 5 fairly flat sections. Each section is a rectangular box of 3" x 3" timber with a single diagonal. Inside this framework is piled a mix of broken brick and mortar. The outside is then mortar rendered and the inside is plastered. (The curved skirting board, instead of being kerfed wood, is actually a moulded plaster sweep across the entire bay!)
I don't think I could remove the bricks etc without disturbing the render on the outside. In reality, I think the infill and the outside render are probably one and the same!
You mention membrane -- what sort of membrane? PVC sheeting? Butyl?

--
-blj-

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On Sat, 17 Feb 2007 23:32:35 +0000, Brian L Johnson wrote:

===============================I think you've established that it isn't just rubble filling the void so the next step is to discover what exactly this hybrid wall (timber / rough brickwork) is supporting. Obviously it's supporting the window frame but you really need to discover how much support it's giving to the roof of the bay. It would be sensible to ask a local builder for an inspection to decide this. Depending on what you find it may be a quite straightforward job (but messy) of removing the whole of the existing wall and replacing with a new wooden structure (with insulating infill) covered on the outward side with a membrane.
This kind of replacement can be done piecemeal without disturbing either upper or lower window frame provided that adequate support can be provided whilst the job is in progress. The structure of the bay roof is the important thing to be sure about.
As far as the membrane is concerned heavy duty polythene sheet is used but a visit to your local builders' merchant should show you if there's anything more modern.
Cic.
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Cicero wrote

Good points. I'll have one of the local builders (my brother-in-law has just used a good one) to check out the situation with the bay roof.
Apparently the old wooden windows were replaced with the current PVC ones about 8 years ago. I imagine that they're much heavier than the originals -- which means that it's more important than ever to determine the state of the wall's internal wooden framework.

Ah, I see now where you're meaning the membrane to be used. Yes, I'll have a look to see what's available.
Thanks for the advice. :)
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On Mon, 19 Feb 2007 08:13:40 +0000, Brian L Johnson wrote:

==============================Just a small but obvious point; if you do replace the wall you can use almost any kind of exterior cladding as an outer shell. Tiles are commonplace, uPVC is clean and durable - the possibilities are almost endless.
Cic.
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On Mon, 19 Feb 2007 08:13:40 -0000, Brian L Johnson

PVC windows need to have the cills carefully sealed where they touch the wall reveals. There also needs to be an expansion gap there. If these gaps are not sealed then water could enter the fabric of the building. Possibly any screws used to attach the cill to the bay could allow water through.
Maybe go up a ladder and see if there is anything that looks like it could do with sealing with frame sealant.
Another thing , look under the cill and see how it is sealed. Look at your neigbours houses maybe there should there be flashings there and the fitters didn't bother refitting them?
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Sounds like youre going the wrong way about this, http://periodpropertyshop.co.uk/phpBB2/viewforum.php?f=1
Whatever you do, batten/insulate is surely needed with 4" walls, theyre expensively conductive.
NT
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"" wrote

I can't quite find a topic there that directly pertains to my problem. Is there something there that I missed?

Very true!
My worry, though, is that battening on to this wall will just rot because it will get soaked. Is that not the case?
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First read would be the damp FAQ, search for that thread. Then describe and ask them about your situation.

You've got 2 prolems to solve. Of course the damp issue needs solving as well, otherwise as you say it'd rot. Insulation needs to be part of the eventual solution though, otherwise condensation is going to be hard to stop, and you'll be wasting much money on heating.
NT
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"" wrote

Okay, so there're not in favour of tanking, and it looks like I should be stripping off the outside rendering and replacing it with a lime- based render to allow the water to escape.
That'll be tricky because taking off the existing render will expose the broken brick and mortar-mix interior and, in that case, I may as well rebuild the wall entirely.
Which may not be a bad idea.

I suppose that until I've sorted the problem, it's hard to tell how much money I was wasting on heating!
Anyway, until winter has finished, I think I've just improve ventilation around the wall and tackle the job during the summer months. :)
--
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its one option anyway

might help to calculate it & multiply by how many years you'll be there.

NT
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