I have made up my formwork, and rolled out my Visqueen, so that the DPM covers the ground and goes up the forms, making a plastic "tray" to contain the concrete, which is in place.
When I remove the forms, the slab will be left there, with DPM up the sides, ready for me to backfill up the edge. Is that all I have to do? What about precipitation, do I need to do anything apart from make sure the backfill presses on and keeps the DPM approximately in place? Should I be keen to stop water getting between the edge of the DPM and the concrete slab?
I am not sure that the idea of "loose flappy bits" (!) is a good one, or what to do about it, if anything.
Advice?
A supplementary question about slab,forms and dpm. - What to do bout the edges of the dpm?
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MRRB
- Posts: 18
- Joined: Wed May 06, 2020 6:00 pm
- Location: England, UK.
OK, to add to that: the Visqueen was turned up the inside of the forms, and stapled to the top. There is only about 2" that could be folded in and pinched under the prefab posts and sections, and there will be staple holes in anyway. I could cut some more DPM, take it down the edge of the slab itself (folding the 2" under as before) and bring a longer return on top, and trap that under the prefab sections, but the exposed edge on the outside would be liable to mechanical damage or exposure to the sun/elements. I could paint the sides of the slab with bitumen DPM which would hopefully stay put. I don't know what to do. I suppose I have done something I should not have done, again! Bother it.
Anyway, I'll have to think about that while I cut and weld the existing trusses to reduce the overall height of the building to less than 2.5 metres. Any helpful ideas most welcome.
Edit: Lawks, I've been looking at "pavingexpert", https://www.pavingexpert.com/concrete and under the "keeled slab" which is what I have made, it shows the DPM turned up the edge of the slab and held there by soil backfill. Well, that's OK, I can do that, BUT it shows "ensure at least 150mm between edge of slab and garage structure", and having copied the setup of the old slab at the place I bought the used garage for 99p, I have only 25mm between the edge of the slab and where the structure will be. Oh dear, another error by the look. What's THAT going to mean, the whole thing will collapse? The edges where it's "keeled" are 200+mm deep, the keels being 600mm wide before floor depth changes to 100+mm deep in the middle area.
Anyway, I'll have to think about that while I cut and weld the existing trusses to reduce the overall height of the building to less than 2.5 metres. Any helpful ideas most welcome.
Edit: Lawks, I've been looking at "pavingexpert", https://www.pavingexpert.com/concrete and under the "keeled slab" which is what I have made, it shows the DPM turned up the edge of the slab and held there by soil backfill. Well, that's OK, I can do that, BUT it shows "ensure at least 150mm between edge of slab and garage structure", and having copied the setup of the old slab at the place I bought the used garage for 99p, I have only 25mm between the edge of the slab and where the structure will be. Oh dear, another error by the look. What's THAT going to mean, the whole thing will collapse? The edges where it's "keeled" are 200+mm deep, the keels being 600mm wide before floor depth changes to 100+mm deep in the middle area.
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Tony McC
- Site Admin
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We cut visqueen or any other DPM only if there is no other option, and, when we do cut, we tape-up as required to return it to being Damp Proof and watertight.
On the drawing to which I think you are referring, the DPM would, initially, been held in place by formwork or the sides of the excavation, not by the paving,m which, obvipously, would not have been there prior to the slab being poured.
The requirement for a minimum 150mm 'spread' at the edges is a "strong recommendation" and what should happen unless there really is no alternative. It's not the end of the world that you couldn't manage it....sleep easy!
On the drawing to which I think you are referring, the DPM would, initially, been held in place by formwork or the sides of the excavation, not by the paving,m which, obvipously, would not have been there prior to the slab being poured.
The requirement for a minimum 150mm 'spread' at the edges is a "strong recommendation" and what should happen unless there really is no alternative. It's not the end of the world that you couldn't manage it....sleep easy!
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