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Damp proofing workshop floor

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Max Power

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I'm in the process of building a workshop on an existing slab that used to have stables on it and has no dpm in the slab. Its around 9 x 5m and I've had 3 courses of blocks laid with a dpc and the rest will be timber.
Are there any specialised coatings I can coat the floor with that will prevent damp rising or isn't it likely to be a problem ? The slab will be completely covered by the building and will have guttering in place.
 

MikeG.

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I suggest that you are probably better off without any internal coatings. If there is damp, the place to put the barrier is on the outside, not the inside. The very basic notion here is that outside the water pressure is pushing the tanking onto the structure, whereas on the inside, it would be pushing it off. With its former use there is every chance that the concrete is a farmer's mix, which is designed to resist the corrosive effect of animal pee. I wouldn't be confident of its compatibility with any possible surface covering.

In lieu of tanking, the first thing you should do is make sure that the external ground level is at least 50mm down from the top of the concrete all round. This has a really positive effect on drying off the outer edges of the slab. Dig the ground away, and install small retaining walls if necessary. You must obviously also deal with surface water properly, and make sure there are no other obvious sources of damp.
 

Bedrock

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Whilst I agree with Mike G that the floor level should be at least 150mm/6" above the surrounding ground level, it was standard build for new build for the top soil to be excavated, blinded and then 6" of oversite concrete before the dpm gets laid. This would then be covered with insulation and say a 2" finishing screed. This was pretty much what my builder used when we moved into our current home which needed major works.The water pressure issue arises when the floor level is below the ground level. In our case, the floor needed tanking, and the builder included what looked like a heavy duty bubble wrap.
There are several alternatives for dpms, but if you go to your local builders merchants you can see what is available - it is usually in the form of what looks like a thick plasticised sheet, and bought in rolls.
If you can run to it, I would include floor insulation, as standing on a concrete floor for any length of time can get cold in the winter months.
 
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