Insulation for thin slab pour

Unknown

Strangely forgiving a radiant floor can be.

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Ernie_4

Thin floor pour insulation

My question is on a thin slab pour (1 1/2 ) over the top of existing subfloor, what type of insulation would I need between the concrete thin pour and the wood subfloor ? I was told to use tar paper, but was worried about the petroleum base on the tar paper would react with the pex tubing ? And maybe break down the integraty of the tubing . On the same install I am also installing wood sleepers to nail down 3/4" hardwood flooring as a finish floor

SVDW

I would absolutely NOT use tar paper as it sometimes smells like a highway when it heats up. Probably ask the flooring manufacterer what they would recommend with their product for starters, then clear it with the contractor who put in the tubing so the system works as he designed. Good luck & have a radient day.

Dan Joyce_4

Insulation thin slab.Tar paper NO no

Tar paper will give off unpleasant when heated up.
Heatway,s (now Watts)Entran,s installation manual 1997,pg. 27 actually address this situation.
Actually saw this happen about 10 years ago.

hr

Do you mean isolation?

As the insulation should be below the floor. Much more room for R value there

6 mil plastic would be a good bond breaker for concrete over plywood or OSB. The only downside is it is very slippery. I've seen some brands with small dimples to lessen the slip factor.

Concrete finishers hate plastic under the pour as it slows the cure time! But it needs to be there for concrete over wood.

I imagine asphalt impregnated felt paper would be fine considering the temperatures slabs generally operate at. 140 is about max for concrete, I doubt, or hope, you will need anywhere near that temperature and felt paper can handle 140.

I've only once seen a problem with felt paper off gassing. It was a rubber staple up system running very high temperatures to meet the load, due to a very thick build up of flooring materials. In excess of 160 supply.

hot rod

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JohnWood1

bubble wrap........

Used bubble wrap style insulation on a similar job... for my own office as there was no edge or back insulation on the existing slab. Rolled out bubbles, laid out 3/8" Kitec and attached to existing slab with emt clips and a ramset. Poured 1.5" of fiber reinforced 'crete over this and put the heat to 'er. Worked very well for me.

jw

JohnWood1

bubble wrap........

Used bubble wrap style insulation on a similar job... for my own office as there was no edge or back insulation on the existing slab. Rolled out bubbles, laid out 3/8" Kitec PAP as it would not float up, and attached it to existing slab with emt clips and a ramset. Poured 1.5" of fiber reinforced 'crete over this and put the heat to 'er. Worked very well for me.

jw

Unknown

Apparently, you only needed a 1.5 R value under your slab for some reason.

Phil_6

tar paper

I don't know about anywhere else but here on Long Island every tile floor set on concrete has tar paper under it. Never been a problem. Tar paper, wire, pex, concrete and tile, in that order.

Unknown

Absolutely. Some people even install pipe in joist bays without plates and it "works great" too!

Ain't thermodynamics an odd bird, eh gary