Can’t really find a good answer to this one. Scenario: New England climate, frost walls are already in, gravel backfill up to 12″ below the bottom of slab elevation. Architect design has several openings so that the slab essentially sits on depressions in the frost walls. The building is an open pavilion, no insulation, no heat, essentially open to the elements. Concrete contractor wants to come in and place poly sheeting under the final 6″ of crushed stone before he pours the slab.
I am curious as to why he wants to put the poly under the stone and not right under the concrete. For that matter, why put the poly in there at all? Second, should I be worried that the slab will act as a bridge over the frost walls, allowing for settlement and the possibility of serious cracking further down the road?
Replies
If I recall correctly, it's common here (Atlantic Canada) to put a few inches of gravel over the poly....to prevent holes poked in it during the pour. The gravel is carefully spread, of course.....if'n you have the poly lying there, then everyone walks all over it during the pour, and you might as well not have it.
Those sharp little rocks turn poly into cheese cloth...
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Well, you have to pick your gravel carefully.
You can pick your friends, and you can pick your butt, but you can't pick your friends' butt, at least not more than once!
So who gets that sortting job...
You useing river rock???
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
The concrete finishers like poly under the slab because it slows the set up time allowing more time for finishing, especially on hot days. Also it allows the concrete to cure better, over time, by not having the moisture in it absorbed into the gravel quickely.
Why he placed it under the gravel I do not know, compaction might tear it up a bit and it might negate the above reasons. I have always seen it under rebar and above gravel.
having some gravel between the poly and the crete will let excess moisture seep in. With poly immediately under the slab, the moisture will float to the surface making it take longer to cure, and possibly making it scale off. i can see wanting to keep poly close in a hot climate, but not in cool damp weather.
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