Damp Sandstone wall with cement render

[sandstone and cement]

Help! I have a flat in a converted detached sandstone building. The gable wall is roughcast rendered and both mine and my downstairs neighbour have damp issues with this wall. This sounds obvious, remove the render and repoint in lime. BUT I've just had a damp survey done and it states that that wall was originally an internal wall as the house was originally part of a row of terraces.

Surveyor did not suggest to remove cement render but instead to replaster the internal walls in lime to allow wall to continue to dry out, however researching this it seems if the cause of the damp (presumably the non breathability of the cement render ) is not addressed the lime plaster will also stain and deteriorate.

Has anyone solved a similar situation ? or can anyone make any suggestions for how to deal with this? at the moment the internal walls are hard plastered with gypsum with dab and dot in one room (or possibly both) I was thinking a timber frame , with fermacell or other breathable alternative instead of plasterboard but not sure this will aid with drying the wall whilst cement render is there.

Really appreciate any in put!

 

[Cassie]

I am definitely not the right person to answer this- there’s a ton of very experienced advice available here! But having recently removed dry lining on top of cement render in my house, the cement underneath was saturated and on removal of that, so we’re the bricks underneath, also badly deteriorated. Barring the places where there are leaks (impossible to determine under cement) the bricks are drying out nicely and with repointing and plastering with lime I hope will last a few more years. I’d be very cautious of trying to dry line over wet cement, I doubt any good will come of it, but of course I’ll defer to people far more knowledgeable than me, whom are a plenty on this forum! Interesting that the surveyor didn’t suggest removing the cement- maybe some reason for that? My surveyor was very disparaging of all of the “unsuitable “ wall coverings and recommended stripping out and replacing with lime wherever possible

 

[malcolm]

If you have a downstairs neighbour I'm going to guess you are not at ground level. The only time I had trouble with damp on the first floor was before I removed the waterproof covering on the exterior of my wall.

It's madness people went around waterproofing the outside of their walls. Removing that waterproofing allows the water to evaporate away so it doesn't build up and cause problems inside.

Removing the cement render and the waterproof paints on the outside of the wall should fix any damp you have up there. Interior finishes aren't too important on the upper floors. Worth checking that roof drainage and gutters are working properly.

 

[CliffordPope]

Would the fact that this wall was orginaly intended as an interior wall make any difference? Is sandstone porous, or are there perhaps different types depending on the intended location?

 

[stuart45]

Sandstone is porous, although some types are more porous than others. Soft masonry units don't necessarily allow more moisture through the wall than hard non porous ones. Google the raincoat/overcoat effect on walls.
The problem with a wall intended as internal would be the way it was constructed. Sandstone should be laid on it's natural bed to protect it from the weather, but on an internal wall the masons probably wouldn't have taken such care.