How do you secure foam for slab pour?

[NuthinFancy]

Getting ready for the pour of my slab-on-grade floor (5" slab with thicker perimeter) and got to thinking about the 2" XPS foam (OC Formular 25) that will be installed (by me) ahead of the pour.

How the heck do you keep this in place on top of the gravel/traffic-bond?

I expect some movement when the concrete hits the foam, but I'd like to minimize this. (I plan to put 10-mil poly on top of the foam as a vapor barrier.)

TIA

 

[Randy in Maine]

I used the 5'x9' sheets of about 6"x6" of heavy woven wire (from the concrete shop) on top of the 2" insulation/pex tubing. Worked great and easy.

I put the vapor barrier below the insulation although it probably doesn't matter.

 

[wssix99]

I assume you are pouring your slab before putting in the walls and you don't have foundations?

I would expect that your concrete finishers will need gauges in the slab to get the proper thickness and will puncture your foam, anyway - so, you may concider putting some rebar stakes through the foam in a few places and have the pins stick out by 5". Your concrete company can then use the pins as gauges to make sure they get the proper thickness for you and they can pull them out as they go. You would only need to lock in a few sheets and the rest should stay in place.

At a minimum, you could use rebar pins to secure the edges of the foam between your forms. I had mine laid down between my foundation walls and the panels had no "desire" to move around, even before I added our PEX. You can also tape the sheets together.

 

[larry4406]

...I put the vapor barrier below the insulation although it probably doesn't matter.

I thought I read a recent post that recommended the vapor barrier on top of the insulation.

 

[Richard Cranium]

tie it to your wire grid.