Damp issues

[Tommygun3000]

So I’m after some help if possible? I’ve moved into a house which we believe to have been built in 1807 but renovated in 1972, one wall in the living room is below ground and we have high damp meter readings so had a specialist out to take a look, the tanking has failed and they’ve suggested putting up a damp membrane that will feed into a dug out channel in the concrete floor, my job is to remove the plaster before they come but as soon as I’ve started I’ve hit a ‘wall’…I’ll get my coat
All jokes aside it appears to be a skim coat over a material I’m unsure about? It’s not blocks and I can dig my nail into it but it is deeper that plaster would be? Any ideas? Is it some form of internal render??

 

[Glenn586]

Before doing anything further spend a few hours on here and on google researching old walls and the importance of breathability. Your specialist has given you a solution that will just kick the problem down the road for a year or two if you get lucky.

 

[Tommygun3000]

Yeah I’m starting to realize that, definitely a can of worms! But any idea what is behind that skim coat? I understand it’s hard from a photo, could it be an internal render?

 

[a twig]

Looks like it could be a cement render to me, with some sort of tanking slurry over the top?

 

[Ashville87]

View attachment 15016So I’m after some help if possible? I’ve moved into a house which we believe to have been built in 1807 but renovated in 1972, one wall in the living room is below ground and we have high damp meter readings so had a specialist out to take a look, the tanking has failed and they’ve suggested putting up a damp membrane that will feed into a dug out channel in the concrete floor, my job is to remove the plaster before they come but as soon as I’ve started I’ve hit a ‘wall’…I’ll get my coat
All jokes aside it appears to be a skim coat over a material I’m unsure about? It’s not blocks and I can dig my nail into it but it is deeper that plaster would be? Any ideas? Is it some form of internal render?? View attachment 15016

Looks like a gypsum plaster undercoat/browning to me, especially if it’s a bit softer than cement would usually be.

 

[Stevers]

Looks like a cement render to me too, and exactly what you'd expect to find from a 1972 renovation - if stonework there could be up to 1.5" of it in places. The last lot I knocked off, I used a bolster as the masonry underneath was fragile and (being just a chimney breast) not a large area. An SDS drill with chisel bit could speed things up if what's underneath the cement is reasonably sound.

That chimney breast is in my basement. Repointing and rendering in NHL mortars has dried things out pretty well, but perhaps not to the point where you'd want it as a living room. With chimney breast and the flagstone floor busy 'breathing', on some days there's enough humidity in the room for heavy condensation on the single glazed window despite planned and permanent ventilation. There's also some cementitious tanking from 1997 in that room, and where that's working or can be concealed, I've left it, making sure that there's some breathability round the edges of it. I am however satisfied that it will be entirely suitable as a hobby room.

What to do for the best in your situation is definitely open to debate, but a properly detailed and installed membrane must be one option to explore. I'd definitely be concerned that there should be some sort of access to make sure nothing is clogged though if going down that route.

 

[Kearn]

The person you had out was special, but certainly no specialist.

This building should never have been tanked. It always fails, but not until doing substantial, unseen damage.

Have a read through here, Heritage England and SPAB who have great guides. You’ll soon get the approach to how an old building needs to manage moisture.

The approach is simple, but messy and intrusive - walls need to have all impermeable materials removed, pointed / rendered externally in line, same goes for inside. Damp walls will take about a month per inch thickness to dry out, it’s a slow one.

Please keep removing the modern crap. But do not let the damp proofing idiot back.

The squidgy grey stuff is a funny one, I’ve found some of it under gypsum skim in one of our rooms. It’s weirdly still gooey and maleable like playdough after decades.