Drying wet walls old house

[AWaferThinMint]

We've had an issue with damp peeling walls in the house since we bought it. We realised eventually, after investigation, that the drainage from our utility was not right so all the waste water was just being released into the ground underneath the house. It's unsurprising there was such a moisture problem.

It's meant that on what were originally external stone walls (house is 150 years old) but are now internal, thanks to extensions, are just soaking wet.
M we've had the drainage issue fixed now and proper drainage to the sewer installed, so now I need to dry the walls.

It's a large open area in a hall. I have one dehumidifier which I can run in some bits but the air itself isn't damp, I'm getting sensible readings of 40% in the air. Are there any tips for drying the walls and plaster faster or is it just a waiting game?

Put ordinary domestic fans (not fan heaters) to blow air onto the wet walls. The moving air current will accelerate evaporation (like hanging washing out on a cold windy day)

You then have to get rid of the water vapour, either by opening the windows or using a dehumidifier

To dehumidify a lot of water uses a lot of electricity.

Big builders dehumidifiers (the size of a washing machine) are powerful and fast, but so expensive to run that insurers include the cost of electricity in the claim. They do also warm the room but are very noisy.

Otherwise, an ordinary solid brick wall takes about a year to dry out from fully wet.

If you strip off wallpaper and plaster it will dry quicker.

Thanks @PigletJohn.

I have this guy feeling that stripping the plaster is probably going to have to happen at some point so I can dry the stone walls properly. Because of the drainage issue I want to give the ground chance to get to normal moisture level first.

For now I will try the fan, thanks for the tip. Just need my paint to last a few months 😭

You might want to consider whether it is a good idea to pull out all the water so quickly !

Fortunately I guess the water is pooled underneath the wall, and is making its way slowly up by capillary action, so it is probably not fast enough removal rate for it to cause problems. I would still take some expert advice though, as when you pull all the water out you are changing the structure of the ground beneath the wall. My guess is the expert will also know the best way of drying it out.

Maybe you could experiment with some stuff. For example did you try taping a polythene sheet over the wall ? Maybe if the room was cold enough you could get water to condense out on the sheet. Another way might be to put a sheet over the wall and the dehumidifer inside that with some sort of standoff. Be careful it doesn't get too wet inside though as electrics and a lot of water pose a safety issue.

It there is any chance that the walls might be slightly damp in the future, i.e. the building is pre damp proof courses, then I would highly recommend replastering in lime. Even if lime plaster gets wet, you can just dry it out and it won't need stripping off back to brick again.

Thanks @GasPanic I'll beat that in mind. Plastic sheet isn't a bad idea.

@Geneticsbunny I've tried to find someone to do like plaster but have yet to find anyone willing to do it! Trades don't seem to like working with it!

They are probably scared that if they redo it then a load of water will get sucked up behind the new plaster and ruin it, and that you will try to claim off them to get it redone.

I think, having heard what you've all said, I'm going to manage it as best as I can through to summer and see where we are once the ground has had the chance to settle as the water drains naturally. If I keep the inside warm and dry hopefully things settle over time.

If not I'll chip all the plaster off and see if we can get it sorted properly.

Thanks for all your insights. It is appreciate.

More than likely if you are deying out the damp masonry out into the house, it will bring some salts with it which willa)ruin the paintwork and b) continue to look locally damp.

Which means yes you are quite possibly eventually likely to need to replaster. You could try contacting a lime plaster manufacturer directly (eg Ty Mawr) and ask if they have recommended installers - I think the suppliers offer training , so might have a list of their 'graduates' - then you could book someone now, for some point in the future?

Thanks @ValerieDoonican that's really useful.