# Pex in a mud floor



## Splinter (Apr 5, 2005)

The way I see hydronic radiant under tile around here is paper and lath stapled to the subfloor, 3/8" tubing laid, then a 1 1/2" mud bed... 
If the pex is a 5/8" outer diameter, that leaves almost an inch of mud over the top of the tubing. I often see tile installed directly on the mud floor, though I would prefer to see Ditra installed first. There doesnt seem to be any issues with this system from what I've seen. 

Figure a radiant floor isnt really getting that warm anyway. Water temp is supposed to be regulated in a radiant setup. You're not pumping 180 degrees through the tubing. My home system rarely goes over 120 on the coldest days, and my floor temps stay in the mid 70's. I dont see there being a lot of stress on the installation due to temperature.

A moderator on John's tile site quotes some industry standard saying you install the tubing on the sub, fill in with mud to the top of tubing, then a cleavage membrane (tar paper) and an additional 1 1/2" of mud on top with wire buried in the middle. That's about 2 1/4" of height before tile, and probably over 20psf dead load. 
This seems excessive to me. Also seems like it would take longer to push that heat to the surface. Has anyone here done pex in mud? How did you do it?


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## Red Adobe (Jul 26, 2008)

I have only seen / helped do in slab. With that once the slab is cured and solid there isnt that much change in pressures on the pex ( because the crete is set)


The more thermal mass you have the more consistent the temps will be and lower fluctuation or drastic change maybe thats why they want the depth?


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## ee3 (Feb 10, 2006)

Not sure if there was a question there but ,both methods are correct..
TCNA DETAIL --RH-123 OR RH141
Theres still some other methods also..


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## Splinter (Apr 5, 2005)

I'm reading it as RH-123 specs SLC over tubing, not deck mud, and RH-141 is the double mudbed method. (Lower encapsulating the tubing, cleavage membrane, then second mudbed on top)

My question would be: is there any issue (TCNA or others) with doing a single 1 1/2" layer of deck mud with the tubing in it, and an uncoupling membrane on top? What kind of problems could arise with this method that I just havent seen or heard of?


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