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Restoration & Refurbishment

How to treat black mould on sandstone walls?

Anonymous user 01/03/2024 - 2.49 PM

Hi we live in listed building with the sandstone walls. The whole house was refurbished couple years ago, after the heavy rain storms all the walls get damp and inside plaster is covered by black mould/mildew from the floor to the ceiling and on some places is quite bed with the salt flakes and plaster is coming off. We going to protect outside walls with the clear coating to stop the water soaking through. The stones were re-pointed couple years ago so there shouldn't be a problem. The question is how shall we get rid of the mould inside and how to paint it? Is there any special treatment? Additional Yes the pointing is lime and sand..

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2 Answers

ADR Property Maintenance

Rating: 5 out of 5

Boston

really depends on what was used to re-point the walls with, you really need to find out where the water ingress is coming from, black mould is usually condensation. you say lime and sand this worries me as it's normally lime mortar and tends to be referred to lime and sand when the person using it mixes it them self with hydrated lime, builders sand. it doesn't really matter what you paint on the walls if it's water penetration it will fail, sorry but I know a lot of so called expert builders that have re-pointed listed buildings with lime and sand, not lime mortar, as lime mortar is harder to use. good luck Alex

Answered25 March 2014

N G Barham Building Services Ltd

Rating: 5 out of 5

Wells

Was the outer pointing completed with a cement-based mortar? If so, this may be causing or adding to your problem and putting an external sealant on the stones will only make the matter worse. You should have a hydraulic lime point for your stonework, allowing water vapour to escape externally through the joints as well as the stone. Cement pointing can hold water within the wall which can ingress internally causing damp problems. Check this before doing anything else.

Answered25 March 2014