Damp on Party Wall, Please help

4 Sep 2013
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United Kingdom
I have recently bought a semi detached Victorian Property which is constructed from 9inch Solid Brick. I am suffering damp patches all along the party wall. There is a cellar beneath the property but next door have had there’s filled in some 10 years ago, they have also had their side of the party wall re rendered in what I suspect is either sand & cement or gypsum plaster. Both downpipes, front and back of the properties go into the main drains. The party wall on my side also has what I believe is gypsum plaster although I’m not 100% sure. I have removed 1 meter of this plaster to let the wall dry out whilst I decide the best course of action. I have asked next door what they have along that wall and there is barely anything, and no signs of damp there side although I suspect this is being hidden from the new render. I mentioned that the construction of my property is 9 inch solid brick, this is true with the exception of the party wall (where the damp is). The party wall seems to be constructed of a type of rubble, with bits of stone in it, but the cellar wall beneath is again different, this is more like a solid stone, but as soon as it reaches the ground level it changes to this type of earth, rubble with stones in it. (Ive uploaded a pic of cellar wall, and the damp of the party wall before i removed the plaster. I will upload pic of rubble wall asap)
I have read lots about chemical injections and the use of sand and cement with water proofer and I feel i should avoid this as this method would be just sealing in more moister damaging the fabric of the wall and not allowing it to breathe. I have read that the solution may be a lime based render with use of breathable paints which will allow the wall to breathe. However I am worried that I would use the lime render or an alternative that I’ve read about called limelite renovating plaster, redecorate with breathable paints but then still get the damp which would be a lot of effort and money wasted.

Any expert advice would be much appreciated
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1. Perhaps you can determine exactly what material the neighbours used: either S&C render, or a gypsum plaster?

2. Do the neighbours have a solid floor over the old cellar area?

3. How thick is the party wall?

4. Does your damp extend along the whole length of your party wall?

5. Have you removed a skirting & examined the back for decay?
Do your floor joists run into the party wall?

6. A 4:1:1 of sand, lime & cement or a 3:1 of S & L with a remedial finish will, typically, give you 20 years of relief from damp penetration.
Sometimes, its the best solution.

7. Your pics are fuzzy and dont enlarge.
I will check tonight and ask next door if I can pop round to check on what floor they have and to do my best to identify what the render is. I'm worried this might be quite difficult as it is painted over and the owner already has told me they don't know what is on the wall? Is there anyway to tell between s/c and gypsum plaster once painted on?

The skirting boards have all now been removed and the backs were all in fairly good conditions. A little damp but not a lot. The damp was on blotches all along the party wall, so there were some dry areas too. The wall I'm trying to identify I now have a picture for. I'm hoping someone might know what it is and therefore best course of action.

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Sorry Dan. Just realised I have opened two different threads. I've been going into overdrive on several forums trying to get the info I need to assist with this. It wasn't intentional. My plan is to use a lime render and plaster anyway as the help I've been given suggests this is the best idea.

Do you know if it would be too difficult for a plasterer only usually familiar with s/c and gypsum to give lime ago?

Also do you know what the best mix is for using lime on s stone rubble wall?

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