Damp on chimney wall - hydroscopic salts
Discussion
I've done a lot of reading on this but not sure if on right path. We have a bricked up chimney in our bedroom. Spots on the wall keep getting damp.
There has been historic water ingress but fairly sure all fixed now. We added a vent where there was none too and have had chimney and pointing all checked and re-checked. Even though wall was skimmed nothing was done at the time to seal it - so new plaster has been damaged I think.
From what I can work out "hydroscopic salts" can be the problem. i.e. condensation in the room sticks to old salts in new and old plaster. We used just standard plasters back when this work was done.
I've read about various tanking methods and membranes that can be used to fix what seems to be a common issue. The idea is we should hack off all the plaster, fit plastic membrane and board/plaster over it.
My problem is that we have no depth to install all this (because of plaster cornice). The plaster itself is actually totally sound - really rock solid.
I'm thinking I could strip any paint off. Treat the exposed plaster with salt neutraliser. Use a cement slurry (looked at Sika waterproofer) over the whole lot - which should seal the wall. Then leave that for a few months to see if it stays dry before finishing and painting etc.
The wall itself seems dry except where old water damage was - the plasterer used bonding to patch areas too which I think was an error as that seems to act like a sponge for water. We do get a lot of condensation from shower etc. so it seems to add up. Sand and cement with SBR seems to be best.
Anyone any experience? Seems a swine of a problem!
There has been historic water ingress but fairly sure all fixed now. We added a vent where there was none too and have had chimney and pointing all checked and re-checked. Even though wall was skimmed nothing was done at the time to seal it - so new plaster has been damaged I think.
From what I can work out "hydroscopic salts" can be the problem. i.e. condensation in the room sticks to old salts in new and old plaster. We used just standard plasters back when this work was done.
I've read about various tanking methods and membranes that can be used to fix what seems to be a common issue. The idea is we should hack off all the plaster, fit plastic membrane and board/plaster over it.
My problem is that we have no depth to install all this (because of plaster cornice). The plaster itself is actually totally sound - really rock solid.
I'm thinking I could strip any paint off. Treat the exposed plaster with salt neutraliser. Use a cement slurry (looked at Sika waterproofer) over the whole lot - which should seal the wall. Then leave that for a few months to see if it stays dry before finishing and painting etc.
The wall itself seems dry except where old water damage was - the plasterer used bonding to patch areas too which I think was an error as that seems to act like a sponge for water. We do get a lot of condensation from shower etc. so it seems to add up. Sand and cement with SBR seems to be best.
Anyone any experience? Seems a swine of a problem!
Brilliant, thanks.
One part I'm struggling to understand (and I have read elsewhere so assume it must have a lot of merit): If the problem is not really water getting in from outside (rain etc.) then why does painting or coating it with some kind of tanking paint/slurry seem less of a solution than a plastic membrane and new render?
I'd actually agree that painting with some "special" paint seems too good to be true but I don't really understand why it won't work? Or is it more than it will fail a few years down the line from chips to the coating etc.?
It feels less like I'm covering anything up if the water is actually coming from inside the room?
I'd normally just hack it all off but in this case I think it will mean removing the bricked up area as it sits too far proud. It's a lath and plaster wall otherwise too - so will be one heck of a mess stripping it right back. Took us about 5 years to get the dust off everything last time we stripped one!
One part I'm struggling to understand (and I have read elsewhere so assume it must have a lot of merit): If the problem is not really water getting in from outside (rain etc.) then why does painting or coating it with some kind of tanking paint/slurry seem less of a solution than a plastic membrane and new render?
I'd actually agree that painting with some "special" paint seems too good to be true but I don't really understand why it won't work? Or is it more than it will fail a few years down the line from chips to the coating etc.?
It feels less like I'm covering anything up if the water is actually coming from inside the room?
I'd normally just hack it all off but in this case I think it will mean removing the bricked up area as it sits too far proud. It's a lath and plaster wall otherwise too - so will be one heck of a mess stripping it right back. Took us about 5 years to get the dust off everything last time we stripped one!
Cheers again. I'm not 100% sure of everything outside but I've taken a brick out inside and it seems drier the further into the wall I go through mortar etc. Chimney has been re-pointed and has a vented cap on top. Inside the chimney is cold and damp but then it's outside air and been raining a lot.
I can also see a few holes in the lath and plaster further up the wall we filled years back with bonding - the water just sticks to that. That is bonding hanging on laths and not touching the stone wall. We've used modern vinyl emulsion which will be another problem. As someone said its a really old house.
A bit worried about covering anything up - we've so far managed to avoid bodging but this one just had me a bit stumped. Will see what I can hack off and if I can get it deep enough for a good skim of sand and cement (even if I can't do the air gap membrane). That won't take too long and it still comes back will need to go for something more drastic.
I can also see a few holes in the lath and plaster further up the wall we filled years back with bonding - the water just sticks to that. That is bonding hanging on laths and not touching the stone wall. We've used modern vinyl emulsion which will be another problem. As someone said its a really old house.
A bit worried about covering anything up - we've so far managed to avoid bodging but this one just had me a bit stumped. Will see what I can hack off and if I can get it deep enough for a good skim of sand and cement (even if I can't do the air gap membrane). That won't take too long and it still comes back will need to go for something more drastic.
Its the salts part I'm struggling with - I think if I have salts near surface of the wall, the moisture from the room will stick to those salts. Only way to stop salts reacting with the air in room has to be some kind of barrier?
Its likely case that where wall has bricks is ice cold - where rest of room with lath and plaster walls is slightly warmer. Maybe part of the problem?
I expect we have more moisture inside the house these days (compared to when it was built) with hot showers etc. - no issues elsewhere in the house at all though with damp or mould etc. We've not gone too far in making it air tight.
I'm totally on-board with letting house breathe and have avoided use of cement on any pointing etc. using lime. I can see use of vinyl emulsions can be a bad idea.
Will PM you Kurt. Thanks.
Its likely case that where wall has bricks is ice cold - where rest of room with lath and plaster walls is slightly warmer. Maybe part of the problem?
I expect we have more moisture inside the house these days (compared to when it was built) with hot showers etc. - no issues elsewhere in the house at all though with damp or mould etc. We've not gone too far in making it air tight.
I'm totally on-board with letting house breathe and have avoided use of cement on any pointing etc. using lime. I can see use of vinyl emulsions can be a bad idea.
Will PM you Kurt. Thanks.
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