Pouring a thickened edge slab with 12″ stem wall (monolithic) at coastal property. My experience in commercial construction has seen moisture barrier under slab, or nothing at all. Some barriers under crushed rock, some under sand, and some directly under concrete. Engineers, flooring manufacturers, and trades people all vary on needing a barrier or not. Thoughts, ideas, and horror stories appreciated. What’s best! Barrier or compacted crushed rock and a dry concrete mix.
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If you are talking residential - definitely a VB, and in the form of Styrofoam specifically for this (can't recall #), on sand compacted in 6" lifts. If under a garage floor, VB again for certain, but the higher density Styrofoam especially made for the application. It will be req'd for an 'internal' garage (and the bonus is that if you decide to make it habitable, it's already insulated).
All the best...
To those who know - this may be obvious. To those who don't - I hope I've helped.
Thanks for the response. Using V.B. seems to be the overall choice.
If you live in the Sahara desert you may not need a vapor barrier. In many other locations it is required by building code. I can't think any reason not to put it in other than to save $50, but that just isn't worth taking the chance considering it is something that can't be fixed later.
Attached is a pic of one of several houses I've built this year. It is a stem wall house, rather than a mono pour, but it is still pretty much the same thing. A little hard to tell from the pic but the sequence (after the footers and stemwalls) are, from the bottom up: 1)washed stone, 2) termite control chemicals, 3) rigid foam insulation around the perimeter, 4) 6mil poly vapor barrier 5) WWF, 6) rebar 7) pour concrete.
We just had a similar discussion here. Several people had different theories of how it should be done. Not sure if it was just conjecture or what...
Edited 10/5/2005 7:03 am ET by Matt
all concrete slabs, no matter where you live. VB just under the concrete on top of sand or gravel. purpose: it will keep the concrete water from wicking out of the slab and cracking the slab. After the pour and concrete hardness, it will control ground water, thats why it need to be on top of the sand.
Thanks for info and picture. Trying to make sure to do it right.