Sensitively removing plaster from period house party wall

Yellow_Fern

Hi,
I have a terrace house dating from 1700-1840s. There is a party wall which has water damage due to a leak from above on our side. The wall might be original but I can't tell but it has 1970s era layer of sand and cement and wet plaster with a gloss paint. As it is blistered and blown, it has to be fixed. A plasterer have recommended just drywalling it but solid plaster is much preferred. I am trying to figure out how to remove the plaster to allow a new hard plaster coat, but I am concerned kangoing would be too damaging and messy. Ideally we would get lime plaster but it just so difficult to get any lime plasterers here and it is an internal wall so not sure if it is worth it. Anyway the plaster I did get, mentioned the risk of lead paint. Apart from the blistering the wall feels very solid, no hollow sounds and I think the sand and cement is still sound. What is the best way to remove the paint and rotten plaster that would not risk damaging potentially very fragile wall core?

Metric Tensor

I have no advice on how to do it but you need to find out the condition of the wall behind the plaster. I have personally seen old brick walls that appeared reasonable on the outside due to cement based plaster but were absolutely destroyed behind it due to leaking water trapped in the wall by the water proof render.

So what I'm saying is don't just examine the perceived bad areas. Check the whole wall!

Roger Mellie Man on the Telly

Use a brick bolster with a lump hammer instead of power tools if you're worried, at least to begin with.

Romer

Got a similar situation here with the exception that the walls are not party walls. What I was advised to to do by a Lime Plaster expert, was play x's and o's on the wall. Tap with a rubber mallet or some such. If it sounds and feels solid, give it an x. If it sounds hollow, draw a circle the size of the hollow sound. When that has been done for the whole wall, if you have more than 1/3 of the wall covered in circles, probably best to remove all the plaster and re-do it. As far as removing all the crap paint and concrete or gypsum skim coat from solid areas, absolute pain in the hole. I ended up getting some fairly stout 4 and 6 inch putty knives, putting an edge on them and using them with the rubber mallet to remove the skim and paint. Soul destroying work. I'm now waiting 6 to 8 months to see how well they vent off the moisture that's been trapped. I'm definitely seeing the difference with a moisture meter.

By the end of this summer I may be ready to tackle plastering it.

Yellow_Fern

Thanks for the feedback. I have started work on this, just gently removing skim coat with a chisel. It is extraordinary how much water is trapped in there. Water nearly dripping out of cracks in the cement.


https://imgur.com/gallery/4bGIMqt

I have finally found a plaster who does lime and cement plastering to have a look. He is talking about letting it dry for a few days, seal with a PVA and then reskim. He makes the point that once the wall is sealed it is stablised and doesn't have to be fully dried out. What would ye think of this approach? Is it risky?

BryanF

Lime plaster was traditionally used for good reason. If you going the pva and cement route what happens to moisture in the wall?

Yellow_Fern

BryanF wrote: »

Lime plaster was traditionally used for good reason. If you going the pva and cement route what happens to moisture in the wall?

Yes I dont really understand his point. Maybe he just wants the jobs done quickly before they are back to work on the 12th of April. Just for clarity this is a party wall with no part facing the weather. The moisture currently in the wall is from a fixed plumbing leak.

henryporter

Sounds like he’s offering the fast option alright -lime plastering is a long slow messy process (but is worth it). I presume you have fixed the leak that caused the dampness? Best to let the wall dry out some before refinishing it either way.

Yellow_Fern wrote: »

Yes I dont really understand his point. Maybe he just wants the jobs done quickly before they are back to work on the 12th of April. Just for clarity this is a party wall with no part facing the weather. The moisture currently in the wall is from a fixed plumbing leak.

10-10-20

I'm not a plasterer, but I wouldn't be using PVA to seal/bond any wall, especially if there is a possibility of further water ingress affecting it.
It needs to be a priming agent, SBR is normally used, but I'm not sure if it's commonly used with lime-based plasters.
https://www.goodwins.ie/sites/admin/plugins/elfinder/files/goodwins/products/downloads/0071044/Data%20Sheet.pdf

Do a google on where you should not use PVA before he starts.
https://www.instarmac.co.uk/support/technical-articles/pva-for-priming-good-practice-or-a-bad-habit/

Yellow_Fern

So in the end we found the sand and cement was mostly sound and still bonded to the brick. We left it in most places. I removed it in a few spots where it was cracked and where water was seeping through. This is a party wall, so it is not rain, so we found the water was coming from a leaking boxed in soil pipe and a leaking soil pipe under the cement slab. So we then put gypsum skim over it the wall. It has tried in most places but has is dried really slowly over the seeps. The plan is to give those a few months to dry, than add a breathable paint. The plaster does lime but he didnt recommend it.

listermint

Yellow_Fern wrote: »

So in the end we found the sand and cement was mostly sound and still bonded to the brick. We left it in most places. I removed it in a few spots where it was cracked and where water was seeping through. This is a party wall, so it is not rain, so we found the water was coming from a leaking boxed in soil pipe and a leaking soil pipe under the cement slab. So we then put gypsum skim over it the wall. It has tried in most places but has is dried really slowly over the seeps. The plan is to give those a few months to dry, than add a breathable paint. The plaster does lime but he didnt recommend it.

Any reason given for not recommending lime ?

Yellow_Fern

listermint wrote: »

Any reason given for not recommending lime ?

He cited that it would be unnecessary cost- 4x price or so. I understood that we took a gamble using gypsum but we have solved most of the leaks and unlike before we won't use glossy paint which seems to disaster in this case.