4 inch gap between concrete slab and external walls
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julia440
Labourer
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Posts: 1
Joined: Wed Oct 20, 2021 8:02 pm

4 inch gap between concrete slab and external walls

Post by julia440 » Wed Oct 20, 2021 9:28 pm

Hello all,
Hoping you can help - there seems to be a 4 inch/10cm gap in my house between the concrete slab foundation and the external walls. The slab is screeded over but the screed is in poor condition so before repairing it we have started taking out loose bits of concrete.
It is very apparent where the hollow gap is under the screed because of the distinct crack all along the perimeter of the property.
I searched for expansion gap but nowhere does it say it should be this big. It is literally filled with dry rubble and dust. The house is a detached cavity wall construction from 1972.
Could anyone suggest what the gap is for and how/whether to fill it?
Many thanks and best regards
Julia
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stoneyboy
Project Manager
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Joined: Wed Dec 10, 2008 6:44 pm

Re: 4 inch gap between concrete slab and external walls

Post by stoneyboy » Thu Oct 21, 2021 9:55 pm

Hi julia440,
Sorry to bear bad news but it looks like the screed is just not thick enough - it has been laid on top of the damp proof membrane. You could liken this to a layer of toffee on a greaseproof sheet, it just cracks.
Regards S

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