Gents,
Perhaps I'm in the wrong thread. I was originally concerned with the place in the slab for the pex tubing. On the bottom of the slab, in the middle? On top of the re-bar, below it?
Let me say one thing about slabs. I have also been in the construction business in California ( heavy commercial) and I have never seen a slab without re-bar. Wire mesh is commonly used in driveways, but every, I repeat, every slab I have seen in my years in the trades has steel in it. Maybe only #3 at 18" o.c. but steel nonetheless. Here in Ca. we have seismic considerations to build to, and the only concrete work I have seen devoid of steel is curb and gutter. Proper compaction not withstanding, Re-bar is absolutely necessary in slabs.
Let me re-pose my question. If I'm using rebar in my slab, assuming it's sitting on 2" chairs, why couldn't I tie the pex to the steel with zip ties, pour a 5" slab and be done with it, If some one could respond to that question I would be much obliged.
Steve in San Diego.

You can. Most jobs get tied to wire mesh and "hopefully" gets pulled up somewhere in the middle. Realistically the mesh sits on the bottom after settling. If you use chairs and rebar and tie it like you stated it will work great. Thats an ideal situation.

that would be a very good method! It gets the tube close to where it should be, keeps the bar in the slab, and still allows enough room for saw cuts, if you do that in your area?

Keep the bar at 18" oc or you risk some floating tube with wider, say 24" oc bar spaceing.

I use #7 bar ties for my tube install, faster, cheaper, and stronger than zip ties. Just don't over tighten them. I use my fingers, not the spinner tool, and just give them two twists to keep the tube on the bar. Like twisting a tie on a loaf of bread

Anytime you use chairs caution the concrete guys not to step on the tube right next to the chair or you can put a nasty kink in the tube on this sharp edge.

I like to see all my jobs pumped instead of raked, pulled, wheel barrowed, or Georgia buggied Saves wear and tear on the tube and the connection to the bar.

hr

JR-
Thanks for the reply. When I said chairs, I really mean "dobies", small cubes of concrete with wires sticking out of them, so they're not really as high as actual chairs, and are usually placed ender an intersection of re-bar, offering much better support for the steel. Thanks for the tip about the ties, that sounds great.
Let me ask about your section for a typical s.o.g. installation. I'm planning on 2" poly foam insulation as well as 2" of sand under the slab. I'm thinking I'll put the foam down on the smooth compacted ground, then the sand followed by the steel and tubing. Does that sound reasonable? I'm also reading a lot about perimeter insulation around the footing. Since the finish floor of the slab will end up 6" above finish grade, I'm a little confused as to how to accomplish this. I can't see having 6" of foam exposed at the base of the structure, so...? I do live outside of San Diego, certainly not a severe winter locale, at our place, maybe a month of days in the 30's, nothing really cold. Could I forego the perimeter insulation and still have an efficient system? Thanks for the help.
Steve

http://www.buildingscience.com/housesthatwork/mixedhumid/atlanta.htm

maybe that helps?

------------------
Northeast Radiant Technology, LLC
-=RFH Design, Supply and Consultation=-
RPA certified Radiant Designer
http://www.NRTradiant.com
rob@NRTradiant.com

Synthetic Industries has a website regarding synthetic fibers and product(Fibermesh) claims to eliminate the need for the 6" wire mesh in a slab. It also is used in ICF walls to eliminate SOME of the rebar needed and speed the process of adding rebar in the ICF walls.

I would research their website and solicit feedback on anyone who has used this product and their results. The website is www.fibermesh.com

What we do to avoid crushing/kinking due to wheelbarrows and people stepping on pipe during concrete work is simply pressure test!
It gives the pipe more rigidity, and easier to find the leak in the event of a puncture.

I'm a newbie from the South, and not a whole lot of radiant experts in Texas. I've seen the light and trying to spread the word of hydronics despite short winters. Anyhow, question is: after tying down pex, pressurizing with 100psi air, and then pour concrete, what IF you see a leak?? Do we do a quick pex repair at leak adding 2 new joints using shark connectors? Also, throwing this out, but at what distance do I use ties to tie the pex to the rebar.... every foot, every 3 feet, or what? to keep it from floating?? Any reference article online you might direct me to for install 101? We're pouring next week, and concrete guy expects me to know my stuff.
Many thanks, guys!

1.5 feet to 2 feet apart on ties as long as you're not lifted to near the surface, and at 3 points around the 180 degree bends.

You don't usually see leaks there, but have a splice kit on hand if needed... fixing before the concrete sets would be best, and you'd need to wrap the splice in plastic to prevent reaction with the concrete if it must be buried.