Drying time of wet wall

[Judym]

I have actually just been reading an old post on this subject which has given me comfort.
For background we bought a property that was once part of a large 1780 built house. The majority of our house was demolished in 1900 to allow a bridge to be widened and rebuilt.
When we bought the house we were aware of a very wet wall in the front ground floor room. Cutting a long story short we eventually found that the bricked up fireplace was connected to next doors disused chimney!
Sending a drone up showed the top of the chimney in a very poor state, sunken with huge cracks and clearly the cause of the water egress.
This was fixed about 6 weeks ago but you can still see the wet marks on our walls. It had been like this for decades I suspect so bricks have been repeatedly drenched for many years so I assume it will take a long time to dry.
My current question is, having previously re-plastered the wall thinking we’d sorted the problem, would it be wise to now hack off the plaster and get back to brick to help the wall dry out?
A hole has been created into the chimney to allow that to breathe.
Thanks all advise welcome.

 

[Cubist]

Hi Judy and Welcome, In my opinion no, its not worth hacking the plaster off. On the one hand, if it appears sound, its not likely to significantly increase the time needed for the wall to dry out to an acceptable level. On the other hand if the plaster shows any sign of 'blowing' or falling away from the wall then it would be best to get rid and wait.

 

[Judym]

Thank you that's helpful. Also upsetting hacking off plaster you've paid to have put on!

The previous old thread i was reading, back in 2015, seemed to be saying that walls can take months, even years to fully dry out.
Would others agree with this as I was becoming concerned that the moisture is still visible.

The readings have gone up slightly with moisture reader too but i'm hoping thats because i'd stopped using the dehumidifer over Christmas and so the plaster not being artificially dried if that makes sense.

 

[a twig]

Definitely, depending on construction there are different rules of thumb, our 18” rubble stone walls took ~8 months to fully dry out after new roof and gutters installed and repointing done.

 

[Kearn]

Things dry very slowly…. Especially when they’ve been saturated. A common rule is 1 month per inch of thickness… assume you have lime on the walls? If so this will slow but won’t prevent the substrate drying. However, if it went onto a saturated wall, there’s a good chance it never actually bonded with the wall properly and you may have issues with its integrity.

your moisture meter is designed to measure the moisture content of wood - all the other things it gets poked into confuse it.

 

[Judym]

Thanks Kearn that is interesting, we could have a long wait then. The old plaster would have gone onto dry bricks, this has happened some time later as the top of the chimney deteriorated. I think because it was the neighbours chimney, building regs in 1900 not being what they are today, meant it didn’t get picked up. It was used as a commercial building for decades too so no one really bothered. All the subfloor was rotten when we revealed it.
I shall remain patient!

Interesting what you say re the moisture meter as it has timber and solid wall settings? Thanks

 

[88v8]

Is that lime plaster?

Gypsum would impede drying, although probably not worth removing it unless you start to get salts on the surface.

The chimney needs a permanent air vent at the base, as you may know. 9" x 3" would suffice.

And some venting at the top. A sealed flue is not a good idea... condensation.
Hopefully there is a pot up there, with an elephant's foot cap or similar.
If there is no pot, a 9" x 3" air brick in the side would be OK.

I appreciate it is not your chimney but you have the problem so best you solve it then you'll be OK.

 

[Roger440]

What type of plaster is it?