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How to resolve salt damp issue in walls

Postby Seasiderseth » Sat Sep 11, 2021 7:00 am

Morning. Thank you for letting me post here to try and resolve a damp issue which keeps rearing it's ugly head. Details are.

This damp problem exists in my own property, which was created by a builder and further exacerbated by a damp plasterer.
I live in a 1930's terraced property in Whitstable, Kent which was built on the old hinterland of marshes near to the town. The house consists of brick exterior wall, cavity and internal clinker block. The cavity has been insulated recently with a fibrous material (the problem existed before the insulation). All floors were originally wooden suspended but ground floor has been converted into concrete with integrated damp membrane. This is where the troubles begin.
The old boy who lived and died here before me would have no doubt experienced damp under the building and the effects from this on the timber floor below. The water table below ground rises and falls with the seasons. During winter it can be close to 12-14 inches below ground level. During summer it drops away several inches but is still there. I believe this forever present water below the floor wouldn't have had an effect on the timber floor if the building had been properly maintained. They would have happily co-existed next to one another, similar to currently existing properties in my street are without any problems. Whatever happened to the existing wooden floor to warrant it's complete removal and replacement I'll never know. What I do know is the replacement concrete floor has created a damp problem on the internal wall not dissimilar to that on an external wall when material has been heaped up against it. The sub base , which consists of trusty builders rubble overlaid with type 1 MOT used for external pavements and roads is about 2 inches above the internal dpc, which is slate. This sub floor has provided a pathway for the damp to seep into the internal walls as the sub base is mostly sitting in water. When I moved into the property 12 years ago I new there was a problem and had spoken with a builder who had done some work for my father-in-law. He'd suggested this could be resolved by removing the first meter of plaster and render then rendering the wall with a waterproofing additive and plastering from floor to ceiling. As it stands 12 years down the line the damp is back on the walls and salts leaching through the old clinker blocks have blown the plaster from the wall in several places (the plasterer didn't account for salts). Even the render is beginning to crumble in places. To try and resolve the issue I have injected damp cream into the lower wall on 2 sections of the clinker block wall. The results were very disappointing.

Short of removing the entire concrete ground floor and sub base and reinstating the old timber floor I'm stumped for ideas how to resolve the matter of water breaching the internal dpc.

My next thoughts are on a sump pump to remove water from below the sub base thus stopping water from getting to the sub base material, which currently sits on a sub concrete floor (which the old sleeper walls used to sit)

Any advice on my next move would be greatly received.

Regards
Seth
Seasiderseth
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Postby stoneyboy » Mon Sep 13, 2021 9:32 pm

Hi seasideseth
You can mess about with concrete rendered walls, damp proof injection, pumps and the like but with the concrete floor above the wall DPC you will never solve the issue.
Sorry but the only successful solution will be to reinstall the wood floors with a ventilated space under them. Regards S
stoneyboy
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