A vapor barrier with a bunch of rake holes in it is still a pretty good vapor barrier. Vapor diffusion is a vapor-pressure x surface area kind of deal, and the rake holes are but a tiny fraction of the total area.

Even the effect on air-tightness of the foam/vb/slab assembly isn't much affected by the rake holes when the poly is sandwiched between the foam & concrete. Sure, concrete is somewhat air-permeable, but it takes a lot of pressure over a wide surface area to move appreciable volumes if air through a 4" slab, and the total exposed area of those rake holes is pretty tiny, and backed up by fairly air-impermeable foam to boot.

jonr: Putting the poly between the concrete & foam in fact avoids trapped puddles below the finish floor in a leak of flood, unless there are huge air-pockets in the concrete to pool the water in. (In a flood or chronic leak situation the finish floor is toast anyway, eh?)

So the air pockets are lifting up the concrete...? Call me a skeptic.

Posted By Bob I on 09 Apr 2013 09:53 AM
Joe Lstiburek, principle at Building Science in Boston recommends putting the poly directly under the cement and above the foam. Given the potential for water saturating the layers under the slab, one wants the foam to be able to dry out by draining into the stone. Putting the VB under the foam prevents this and can result in the foam sitting in a puddle. Sounds like a valid argument to me, so that's the way we do it. Thinking that a layer of poly will, despite joints and potential holes, stop rising water is wishful thinking.

This doesn't make any sense to me. The poly is intended to be a vapor barrier and is not intended to keep water from anything. If you have water rising into your floor assembly, you have a bad design, bad construction, or a disaster. If you have water sinking into your floor assembly, you just have a disaster. The poly goes between the gravel and the foam.

Posted By BadgerBoilerMN on 10 Apr 2013 10:03 PM
So the air pockets are lifting up the concrete...? Call me a skeptic.

You are correct.  The air pockets did not lift up the concrete.  What it did is to displace concrete during the pour.  Later, as I walked over the hard concrete, I could see places where the vinyl barrier was showing through the concrete.  That is why I said that another slab should have been placed over the original.  I hope this now makes more sense to you.