Concrete cover over tubing.

Alan (California Radiant) Forbes

I can't seem to find any design guide with a reference to the minimum thickness of concrete over the tubing to prevent cracking. Is it one inch?

STEVEusaPA

I have 3/4" of wetbed over the tubing with the roll on membrane then tile.
10 years, no cracks (knocking on A LOT of wood)...
For some reason 1" sticks in my head though.

hot_rod

The Concrete Association suggested 1-1/2 times the aggregate size, at a RPA event years ago

Most concrete mixes with 3/4” stone. For thin pours 1/4” pea gravel is best, but it is a weaker mix. Add a lot of fiber to thin pours😲

nibs

@Alan (California Radiant) Forbes If you are going to pour a 1.5 inch slab, over 1/2 pex, use small agregate, add fiber, ( I like the soft fibers they blend into the slab) specify a super plasticizer to reduce water content, water is the enemy when placing, make the mix as stiff as you can manage, I use a tamper with a mark on the handle, for the lazer for leveling. Add fly ash 10 to 15% of portland, but do not reduce the portland amount, makes the mud more creamy and quite a bit stronger. if slab is bigger than 10' in any direction cast in a metal strip for a control joint. Keep the slab wet/damp for 30 days if possible, do not start warming the slab for 30 days, this will minimize edge curl, nice if you can slowly increase the SWT by a degree per day, again to reduce cracking and edge curl. If the slab is going to be tiled, use something like Red Guard and scrim in a 6" wide strip over the control joints, so that the slab can move a little without damaging the tile. Watch the cement crew like a hawk, because the things they usually do are not what we need, but a good finisher is a godsend.