Damp problem/solution

[jones101]

Hi. This is my first post in this very informative forum.
This is the senario: Old 1790 farmhouse cottage single storey with a 1970s 3 bedroom extension added.
Where the old stone wall meets the new extension floor there's the inevitable damp which has destroyed the skirting, caused paper to peel etc.
Possible solution is for me to hack the existing cement and plaster which is non lime, on both sides of the stone wall and replace with lime products.
To minimise costs, would it be ok to only hack 1m or so of the wall? The damp seems to be affecting about 50cm of the wall height. Just to add that there's no DPC in the old bit but there is in the new which butts onto the old wall.
Many thanks.

 

[MatthewC]

Welcome Jones101. I'll be the first (but not the last) on here to ask for photos please.

Your general plan to replace cement/gypsum with lime sounds like the right one, but have I understood correctly - does your old stone wall have cement render or similar on the outside? If so how far does it extend? If you have cement render on stone outside, then you might have difficulty in getting it off without damaging the wall.

How far from the new extension does the dampness go along in the old wall? Is it only near the join? You want to check for any water ingress from above - roof, gutters, downpipes and flashing etc, especially the join between the two structures which presumably has some flashing there? You could have differential movement there which could have caused a split in the flashing. Check also that your ground level is well down below floor level.

My gut feeling is that doing what you suggest might work for the damp but you'll have trouble making the join in the internal plaster look nice and I think you'll regret it. As a compromise I would suggest you do as much removal as possible and leave it bare for a good while to dry out ; in that time you can think about it some more. You might find that the "new" plaster inside is on cement at the bottom but is on lime further up.

Pictures, pictures....