Puzzling damp patch?

[Doug71]

Trying to work out where the damp is coming from in a wall/ceiling.


It's an old house (my mothers) and we are gradually working through the list and getting the damp problems sorted but I can't fathom this one out.

The main wall in the photos is an internal wall (always has been), the one you can just see to the left is external, both are solid brick and have been dry lined at some point, I think laths fixed to the walls with plasterboard over and I think there is Kingspan behind the plasterboard on the external wall. There is a bedroom above.

The floor joist are parallel to the external wall so it's not damp tracking along one of those.

I took up some floorboards above and there was nothing obvious apart from the damp marks on the plasterboard. I trimmed a bit off the end of the ceiling plasterboard where it touched the old wall so damp couldn't go from one to the other but this made no difference.

There are no heating or water pipes anywhere near it.

There is no sign of anything similar on the other side of the internal wall.

I am told the internal wall used to be really damp, could it be damp air trapped behind the plasterboard (might be foil backed) which is condensing when it hits the ceiling? I say this because where the damp patches drape down on the wall is between the laths that the boards are fixed to. Anybody come across anything like this?

I will be removing some plasterboard to take a look behind but wondered if anyone had any other ideas about what it could be?

Thanks, Doug

 

[seanf]

I’m no expert, but we had a recurring damp problem in our last house that showed on an internal wall but was eventually tracked down as travelling from a nearby external one. It was surprising just how far the water went before showing. You seem to have been very thorough so far and covered everything I would check. As it's at a high level I would be looking at gutters, nearby bushes/trees and things like that. Try to check during different weathers, as all can look fine until, for example, the wind picks up and blows rain in a certain direction, etc. Hacking off some of the plaster seems a good idea to at least get eyes on the wet area

Sean

 

[Bingy man]

Assuming the external gutters are in good order it could be an issue with the dry lining- I’m working in a house atm gutting it back to brick . I was hoping to save a couple of rooms as it has been dry lined ( external wall) however there are multiple damp patches now showing up and some are starting to produce mould. I had a discussion with the intended plasterer who told me if the original ( dot and dab) dry lining is not done correctly ( the position of the dabs ) it causes condensation and mould issues from behind . The wall in the pictures is a solid 9 inch exterior wall.

 

[HOJ]

could it be damp air trapped behind the plasterboard (might be foil backed) which is condensing when it hits the ceiling?

Inclined to agree with how you've described, presuming the ceiling boards travel over and past into the void behind and maybe even up to and touching the brick work behind the wall boards, to my mind could explain why the moisture is migrating more along the ceiling rather than the down the wall, when I dry lined my old Cottage I left a perimeter gap on both ceiling and wall boards, but then fitted Gyproc cornice to cover it, which allows in some respects the wall to vent, even though its into the floor and roof void, (that was my theory and I'm sticking to it, never had a problem with mine)

 

[Doug71]

@Bingy man I don't know if dot and dab on an old external solid wall is ever a good idea.

Someone I know recently renovated a house to be used as a rental property, similar to what you are doing they took everything back to bare brick, made a lovely job. It rented out for a good price as soon as it was finished.

6 months later there were loads of damp patches on the walls just like in your photos, tenant left and the owners had to rip everything out including the new kitchen etc back to the bare brick again, as you can imagine they were gutted.

I later found out the plasterer who had done it did it for cash on a weekend so they had no come back. He had actually made a good job of the plastering, he just didn't really know how to deal with old buildings!

 

[Bingy man]

@Bingy man I don't know if dot and dab on an old external solid wall is ever a good idea.

Someone I know recently renovated a house to be used as a rental property, similar to what you are doing they took everything back to bare brick, made a lovely job. It rented out for a good price as soon as it was finished.

6 months later there were loads of damp patches on the walls just like in your photos, tenant left and the owners had to rip everything out including the new kitchen etc back to the bare brick again, as you can imagine they were gutted.

I later found out the plasterer who had done it did it for cash on a weekend so they had no come back. He had actually made a good job of the plastering, he just didn't really know how to deal with old buildings!

Yes I agree, the plaster I was talking to was explaining this issue, he’s instructed to dot /dab in a particular pattern but when he explains that it causes damp patches he’s told to do as per there spec, surprise surprise when the developer complains of damp a year later . I sent him the same photos I sent you asking if this was what he was explaining to me - yes was his reply. He explained it’s good that I’m trying to save my customer money but it’s false economy and advised me to strip the lot and start from scratch. Worst case you may possibly have to do the same but it may only be 1 wall if you’re lucky . I took a wall down a few years back and the entire dry lining came down completely intact- the wall behind and the back of the plasterboard was black with mould - not a pretty sight-and the smell was awful

 

[joncooper27]

If you have solid walls the best way to stop damp is have breathable walls. The best policy is not to Dot and Dab walls as these will always attract moisture.

 

[baldkev]

Assuming the external gutters are in good order it could be an issue with the dry lining- I’m working in a house atm gutting it back to brick . I was hoping to save a couple of rooms as it has been dry lined ( external wall) however there are multiple damp patches now showing up and some are starting to produce mould. I had a discussion with the intended plasterer who told me if the original ( dot and dab) dry lining is not done correctly ( the position of the dabs ) it causes condensation and mould issues from behind . The wall in the pictures is a solid 9 inch exterior wall.

Hiya, whats your plan? I'm not being difficult, just looking to stop you getting grief..... no matter what pattern the dot n dab is in, if the solid external wall is damp ( which sounds like it is ) damp will pass through the dot n dab......

A first step should be vandex or similar tanking to stop the damp penetration, then a form of insulation to stop condensation.... so maybe insulation back plasterboard with board fix foam instead of dot n dab?

 

[Bingy man]

Hiya, whats your plan? I'm not being difficult, just looking to stop you getting grief..... no matter what pattern the dot n dab is in, if the solid external wall is damp ( which sounds like it is ) damp will pass through the dot n dab......

A first step should be vandex or similar tanking to stop the damp penetration, then a form of insulation to stop condensation.... so maybe insulation back plasterboard with board fix foam instead of dot n dab?

The plaster is hopefully coming tomorrow, all external walls will be insulated plasterboard and internal walls just dry lined. The wall with the damp patches has not been stripped off as yet as I want the plasterer to see it as is . New roof and gutters and eventually new windows will take care of any external issues as well as all 4 chimney breasts are being removed. I will mention “ vandex” to him and take it from there. I do though appreciate your input

 

[mikej460]

I would add make sure your gutters aren't leaking or overflowing (look for green algae on the outside walls) and eaves slates are in good condition (water gets through the eaves slates or over the gutters straight down onto the external brick wall and tracks downward and into the house via the dabs). Rainwater will track so may be adding to the dot and dab issue.