Damp Proofing Question

What should i use to finish on top of a damp concrete subfloor where it is known that there is an underground spring & well?

The shop building is a Grade II listed building in a village in Kent that sits on a spring line. The basement of the building is relatively dry (all things considered). There is a small stream feeding a well at a depth of approx 35cm from the finished floor level. After digging a small trial hole, I think a previous builder has laid a layer of gravel, followed by a DPM, followed by a layer of concrete, followed by a double layer of DPM, followed another layer of concrete followed finally by between 3 and 6 cm sand/cement screed. The ceiling height is only 5'10 and so was thinking of removing the screed and laying something smooth that I could paint a 2 part breathable epoxy paint on. Apparently latex floor leveller is not suitable to walk on. A further complication is that there is a 4" fall across the 14m basement length.

5 Answers

Best Answer

I assume by your question that your existing floor is water tight and you only want to increase the head room.
By the sound of your description of the floor construction, it sounds like this was done for a reason, and if you have no damp, I would leave alone, just for the sake of a couple of inches.
If the floor was well tanked, you may have broken this by digging your trial hole.
As for a 4 inch fall, either done by some one who hasnt got their levels correct, or done for a reason, ie falling to maybe a sump pit with auto water pump.
If your intent on reducing the levels it could be costly.

Answered 12th Apr 2011


Member since 29 Oct 2008

With out seeing the floor its hard to say exactly but I would say the answer from B J D Building is a fair assumption and I really would consider leaving it be as it could end up very expensive.


A&R Ground works

Answered 13th Apr 2011

Inactive Tradesman

Member since 4 Jan 2009

I suggest that the top layer is removed , you then build a support frame using tanalised timber batons (this will allow you to level area, then install a moisture resistant board top (although moisture resistant we advise the underside of the boards are treated prior to installation)
leave a 10 - 18mm gap around edge . once floor is installed you can paint with an anti slip rubber type paint. Hope this helps . sales@dampuk.net

Answered 12th Apr 2011


Member since 25 Nov 2009

You need to keep the spring water flowing through
Giving it a good exit ..french drains ?
further investigation is needed
Resolve the situation as damp water flow will cause problems elswhere.
After sorting out water .Part Tanking system can be fitted Polycarb.Type
Board over

Good Luck

Answered 16th Apr 2011

GSI Property Services

Member since 9 Nov 2008

Either leave thing alone as advised. Or be prepared to pay for a full membrane system which would include a sump & pump.

You can contact Sovereign Chemicals or Triton in order to get one of their approved local contractors to give you a price. The manufacturer's rep will visit the site with the contractor to draw up a specification for the job.

The fact that there is a spring means that a tanking system will not suffuce as there is the possibility of very high hydrostatic pressure from below. Soveriegn will not guarantee a tanking systen in this instance and will only reccommend a mebrane system.

No corners can be cut or every penny spent is potentially wasted. For this size basement you will be looking at £6,000 to £10,000. It needs a mambrane wall to floor, an integrated drainage system needs installing to take water to the sump/pump, the sub-floor needs to be checked for structural integrity, the membrane (on the floor) will need a screed on top. It's not a small job. Leave it alone unless you really, really need the space and will see a return on the investment.

Good luck

Answered 20th Feb 2012

Degan Building Services Ltd

Member since 22 Jan 2012

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