Lime based plaster system for damp wall

Question

Hello,

We have had damp wall on the party wall after the neighbour has removed the chimney breasts. We have never had this issue before and  noticed this after they had started work.

After recommendations from the surveyor we have had our side of the chimney stack rendered where necessary and chimney pots fitted last year, however despite this the wall remains damp. The neighbour hasn't fixed his side and also has no soakers where our roof and their roof join plus the hips that have been placed there are very poorly rendered with holes showing through on our side of the roof. 

The surveyor told to use a lime based plaster system and no chemical injections as they believe water is coming down from the chimney stack. 
The house was built in 1929 , and we would like to know what does a lime based plaster system mean, what materials are required and what is involved. We are currently trying to dry out the walls but it's not working.
 Please can someone help.

Edward · Accepted Answer

In a house of this age, a lime-based plaster system means removing any cement or gypsum plaster and re-plastering with breathable lime plaster (base coat, float coat and fine finish). Lime allows moisture to evaporate instead of trapping it. In this case the damp is likely caused by the neighbour’s chimney breast removal, lack of soakers/leadwork at the roof junction, and poorly finished hips allowing water in. Until these external defects are properly fixed, the wall will remain damp and internal drying won’t work. Chemical injections aren’t suitable as the moisture is coming from above, not rising damp.

Farzad · Answer

From what you have described, it does sound more like an ongoing water ingress issue rather than a traditional rising damp problem, especially if the issue only started after the chimney breast removal and roof alterations.

A lime-based plaster system is normally recommended on older properties because lime is breathable and allows trapped moisture within the wall to evaporate naturally, unlike modern gypsum plasters which can trap moisture and make the problem worse.

In most cases, the damaged plaster would need to be removed back to the masonry, the wall allowed to dry as much as possible, and then re-plastered using a breathable lime render/plaster system. The exact materials can vary, but typically involve lime-based backing coats and finishing plasters designed for older solid-wall properties.

However, the most important thing is stopping the source of water ingress first. If there are still issues with the neighbouring roof junction, missing soakers, poor rendering, or gaps around the chimney area, the wall is likely to continue getting damp regardless of the plaster system used.

Sean · Answer

Tank with slurry and use restoration plaster for damp walls, buy online knock out all blown mortar ,I would still inject with the cream into the nearest mortar line to the floor.

Charles · Answer

A lime-based plaster system is a breathable plaster for older walls that lets moisture escape. It uses lime, sand, and sometimes fibres, applied in layers to replace damaged plaster. Helps damp walls dry, but the neighbour’s roof issues must be fixed too.

Best regards, CB Builders & Son

Lime based plaster system for damp wall

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