Hello, I am building an ICF home slab on grade with radiant heat. We are at the stage to lay the 2" foam, tubing and pour the interior concrete floor. My layers from bottom to top are 12" compacted sand, 4" of 1 - 1 1/2" gravel, 6 mil poly, 2" foam, radiant heat tubing, 4" concrete. It's been brought to my attention that the size of crushed gravel may impact the ability for the 2" foam to lay flat and/or the foam will break during the pour. Is this really the case assuming it's a relatively flat surface? I realize I probably should have used 3/4" crush rock, but replacing the 4" rock base at this point is going to be a major process. Trying to determine my options at this point, and whether this is really going to be an issue. Thanks! Steve

As long as everything is level/flat and was properly compacted, you should be in good shape. We use self compacting pea gravel over engineered 3/4 minus compacted rock pad. Footings are poured on top of the pad and the pea gravel fills the void to the 4" EPS insulation layer.

They should use boards to role on if they are using wheel barrows....

I agree you should be fine and have never had a problem myself.

If you're still concerned after the above, perhaps a final layer of sand just to provide a smooth surface for the foam?

seems a vermiculite topping on the gravel could also be a beneficial add before foam.