Broken damp proof render and consequences

[dangemrod]

Our victorian terrace has a history of damp problems. The previous owners had a standard injection/render/skim treatment to rectify this. The thing is - in a fit of rage and stupidity when trying to free up a radiator tailpipe that had got stuck - I broke away a fist- sized chunk of inch-thick render where the pipe passes through the wall. Once I'd got the radiator sorted, I simply plastered in the broken area. The problem - as you may have guessed - is that the plastered-in section has since become extremely damp to the touch and smell. I'm sure the water isn't from the radiator; the rest of the surrounding area is dry and the water pressure is stable (if a little high). We have put a lot of time and effort into this house, so am now having hysterical visions of all moisture migrating to this one spot once we finally decorate the place!

So, before I do anything else reckless, I thought I'd consult the collected wisdom here for a solution. Would some kind of paint-on barrier do the job of the broken render and protect the surface plaster? Or should I replace the render? If the latter, what exactly is it made of?

[Stuart Noble]

I think I'd want to verify this by knocking out the new plaster. "Extremely damp" sounds like a leak

the rest of the

[Andrew Gabriel]

I'd agree.

Gypsom plaster will wick moisture through, so you'll have to remove what you put in. If it's been wet for a while, that should be easy.

Do you know if the wall was internally tanked to prevent moisture coming through? This might be the case if it's below ground level. If so, it will need the tanking properly repaired.

If not, then use a sand/cement and waterproofer scratch (under) coat, and then you can apply gypsom plaster finish coat on top. Wrap the copper pipe to protect it from the cement.

[mail]

Dear Dangemrod

Penny to the pound you have not put back in render to the dpc spec but have put in a gypsum-based material which has allowed the hygroscopic salts present in the brickwork to permeate through to the finish plaster cure is to remove all traces of said plaster hack out more render such that it is excavated like a dental filling with a greater area of removal adjacent to the wall than visible hole on the surface this can be done in a moment or two with an suitable angle grinder roughen up the surface by keying brick and disc cut render apply coat of SBR bonding additive and whilst still wet a spatter coat of 3:1 sand cement render 12 mm thick containg glue (sbr) and SIKA No

1 Let is set but not dry apply further coats of same till 2 mm left and finish off with multi finish if fussy remove 25mm of finish on old plaster to spread joins and minimise cracking Chris

[meow2222]

Better ask the folk with the subject knowledge on the pp forum: