Mud base w/ no reinforcement

dk816

I am revisiting this from a different angle, my question is about the suspended mud slab for radiant heat. I am using a 1-1/2" thick dry mix 1:5 portland/sand on the sub-floor with a poly vapor barrier under the mud with sleepers for the area with a floating, engineered, wood floor - designed for radiant heat. Under the ceramic tile floor portions I plan to use poly and lath, and no sleepers. From my days as a tile setter we used felt and lath on the floor, I suppose poly is good too. As for the engineered wood floor areas I am not using any reinforcement.



Here is what I am thinking, the poly underneath the mud base is a slip sheet and the 2x2 sleepers every 2-3 ft act as expansion/contraction joints. Also radiant floor tubing is often stapled up under the sub-floor or used in warm board directly under the flooring so there shouldn't be any issue even if there was a crack over the tubing. Am I right in thinking that functionally this floor should be fine. It will provide as a heat sink primarily and also some support for the floor. Any thoughts about integrity? I shouldn't have to worry about it breaking down should I?



It will have a couple of months to cure and after several weeks I will put the heat on to make sure it is really dry before the floor goes down. Please advise on anything - this is a very permanent project and I don't have enough experience to know if the application is sound. I am saving myself $7,000 by doing this instead of a gypsum pour. Any help will be greatly appreciated.







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hot_rod

a couple suggestions

One is the joist sizing under suspended slabs. Joist span tables show the amount of allowable deflection. Some installers drop down to a tighter deflection number, up size the joists basically. L-360 for example would allow 1/3" deflection over a 10 foot span. You need to add the dead load weight with the live load to size. check with some joist sizing guides.



It's the movement in the framing that can cause cracking and failure in a thin slab. Probably not a structural failure, more like hairline or larger cracking, or a bouncy floor. Noticed mostly when dancing .



As for the sleepers and wood flooring, plan the loops so you don't end up cutting across the sleepers multiple times. It's tough to keep small sleeper lengths fastened nice and solid.



For sleepers, considered engineered lumber, like the finger-jointed studs and framing that is available. It tends to stay straighter and resists cupping, bowing, twisting and all the other problems common with dimensional lumber cut from young harvest woods.

Glue and screw the sleepers to the subfloor.



hr

dk816

Couple more questions

The floor was engineered for this floor by a structural engineer.



If I glue and screw the sleepers to the sub-floor I would have to put the poly over the sleepers. Or could a paint the floor to act as a vapor barrier instead?



Do you think lath or some type of reinforcement is needed, or would be best?



Is it okay to put the pex-al-pex tubing on top of the lath?



Thanks for your suggestions hr