My slab is; poly, 2" foam, #4 rebar on 2' squares, 6"x6" mesh, 1/2" pex (with O2 barrier), "chaired up" 2" and tied. 5" pour. in that order.I dont want to spin this thread in a different direction and want to concentrate on doing the floor correctly, but as far as the concrete slab goes.......
to use wire mesh and tie the pex to the wire or a fiber mesh and fasten pex to the foam board?
I had my system designed by a radiant co. and all that I know is by following their plans. (I did the install). I had a discussion with them about placement of the pex, they basically said that it was better towards the living side of the 'crete but that overall it didn't matter that much. (if you wanted to put it down first) I just figured that it was better to put the pex in last, to avoiding dragging around all that steel around on it! Make sure that you tie it all in (your pex loops) to one big loop and put about 60psi air pressure with a guage to watch for 24 hrs. before and during the pour. And have the necessary stuff on hand in case it gets damaged while pouring.
Oh, take a ton of pictures, with reference points before you pour, and make and follow a drawing in case you need that info later, plumbing? drill to mount machinery? etc.