Damp Proofing

rising damp from new concrete floor where chimney used to be

Anonymous user 15/03/2024 - 2.40 PM

I have a detached bungalow circa 1920 renovated it 8 years ago and removed chimney stack. The room has a rising damp issue, we lifted the floor to see underneath the walls are very wet, I have a damp inspection report, part of the recommendation is to remove the new concreted floor which was put in when the old fireplace was removed as it is now soaking wet and a possible cause of rising damp? This leaves me wondering should that area not of been concreted by our builder and what should of been done and what will we do in that area now? Should there be just wood beams fitted like the rest of the floor underneath or do we replace the concrete but put some type of membrane under it or can we leave it there and put a membrane over the top?

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Rating: 5 out of 5

5/573 reviews

Mill Hill, London

Chimney breasts, fireplaces were rarely fitted with adequate damp proofing with regards to a DPC when built due to the lack of requirement. You would be using the area to burn coal/logs etc which would heat the area up and dry it out. Furthermore, the hearth itself is just a concrete slab placed upon damp earth. The concrete will readily absorb the moisture from the earth and transfer it to the surface. Any new concrete works to this area should always include a damp proof membrane (DPM) to provide separation from this earth and leave the concrete nice and dry. If you wanted to remove the concrete in its entirety, this is also possible by extending your existing suspended timber floor across into this space. Andy. (Refresh PSC)

Answered21 June 2018

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Anonymous user

Don't put anything on top. You'll just make the matter worse. Please bear in mind there is no such thing has "rising" damp. This is a confusion with "moisture absorption". All bricks, stone, masonry and timber will absorb moisture they are in contact with. For centuries builders have got over this problem by making sure the material is not permanently wet, by using lime mortars, guttering and in the case of suspended floors, ventilation. You should have air bricks or vents around the base of the property on the outside. These should be clear of debris and above ground level preferably front and back. This provides constant airflow under the floor and keeps it dry. If they are removed, blocked or built over moisture will build up under the floor and condense on the timber, bricks and concrete etc. Hope this helps.

Answered28 June 2018

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