Liquid vs sheet DPM

6 Feb 2014
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United Kingdom

Is it possible to pour a new concrete or screed slab over liquid DPM? or do I have to use a sheeted one?

I have a detached garage with no DPM (or a failed DPM) in the rough concrete slab floor.

I've toyed with the idea of laying a sheet DPM and pouring a new screed floor covering over that but I'm not sure I can be bothered with corner folding and jointing tape and all that, and thought that "painting" a liquid DPM would be much quicker and easier.??

Any thoughts?
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some people prefer it to plastic sheet because they think builders run about on it in their hobnailed boots, dragging pickaxes and mixers and puncturing the sheet.

Do you know how thick the old concrete is? If not very, you might break it up. You can drill a hole in it to see.

Good tip is to slope the garage floor a bit so that any water will drain out through the big doorway.
Old slab is about 300mm thick... My plan is to lay a single course of bricks around the inside (offset from existing walls for a cavity gap), Lay or "paint" a new DPM across the floor, up and over the bricks, fill the brick area with screed and build internal stud walls on top of the bricks.... Leaning toward liquid at the moment, seems easier (if a bit messier) than trying to fold cut and tape around piers?
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I have started to lay the single course of bricks around the inside. However the existing slab is not perfectly level and drops out in one area. 90% of the bricks sit on about a 15mm bed of mortar, but in the area where it drops out the mortar will need to be about 40mm thick in order to keep the bricks level. Do you think 40mm is too thick?... the plan is for the bricks to support insulated ply lined stud walls so not a huge amount of weight.
Yeah you can do a thick bed, or use tiles/brick on edge if that’s easier.

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