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framing walls on a concrete slab with radiant heating

Posted by martyl11 (My Page) on
Fri, Dec 23, 11 at 21:49

I recently replaced the slab on the ground level of my split level home. I ended up gutting the entire level, doing it again from scratch. The new slab has radiant heating.

The contractor (IMHO) didn't do a good job with the framing -- it wasn't straight or square. I also have pocket doors, meaning the framing by the doors are 1 1/2" thick (they used 6" walls). When I looked at it with a straight edge and square, they agreed, and banged it into place (they used liquid nails). But "banging it" after the glue dried would "upset the bonds which formed" (IMHO).

In addition, too many stubs were warped, which caused other headaches (they ripped 2x6's, I don't know why they didn't just buy 2x3's unless they have a saw fetish).

From what I found it, you can use IR imaging to know where the radiant heating tubes are, so you can use mechanical fasteners where there are no pipes (I told them about this after the fact and they expressed "surprise"). They're hoping the tile holds the walls in place (but I think the walls should hold themselves).


Follow-Up Postings:

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RE: framing walls on a concrete slab with radiant heating

Do you have a question, or are you just venting?


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RE: framing walls on a concrete slab with radiant heating

I would not be too quick to sell that liquid bonding material short.

Back in the early 80's I was working maintenance for a large municipal school department and we an area where we needed to use the tubes of liquid nail, but like you, we were a bit skepticl of how well that stuff works, so we decided to give it a test.

I took a 4' piece of 2x4 and cut off about 6", then I used the liquid nail to sister the cutoff piece to the side of the remaining 2x4 on one end and I put it in a vise to clamp it.

I left it in the vise overnight, and the next morning I took it out and clamped the short piece in the vise and tried breaking the joint by both lifting an twisting on the longer piece of 2x4.

After two of us grabbed the 2x4 and pulled on it as hard as we could causing a twisting force on the joint, the joint finally failed, but when we examined where the two pieces of wood had been joined we discovered the glue had not failed. The wood on the shorter piece of 2x4 had split amd sheared away, which accounts for why the joint finally failed, but the actual wood to wood glue joint was still intact.


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RE: framing walls on a concrete slab with radiant heating

Not venting, wondering what an effective way to fasten interior walls to a slab with radiant heating.

Liquid nails does not recommend to fasten walls without mechanical fasteners (I asked them).

Liquid nails also recommends to cure the bond for a day before using it -- if you glue and put up framing in the same day I wonder how effective the bonds will be.

If you hammer at a glued sole plate to straighten it out (several weeks after framing) it seems the glue bonds would shear.

From experience, it seems full walls (4" or 6") hold well. But the 1 1/2" sole plates for pocket doors didn't hold well
(they ended using tapcon screws at the end of pocket door frames).

Should the walls by themselves be secure? Or is the theory "the tile will keep the walls from moving in the future" adequate?

(I agree with lazypup that the bond could well be stronger than the material -- if its used right).


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RE: framing walls on a concrete slab with radiant heating

"they used liquid nails"

Not normally used as a structural material by itself.

Even for drywall it reduces the fastener schedule, but does not eliminate all fasteners.

Since these walls appear to be partition walls, they do not require extensive anchoring.

You probably could have gotten away with fewer and larger fasteners (3/8 inch diameter) and not bothered with adhesives at all).

If you stil have heating lines marked, I would go back and use at least tapcons (it will require more of them than a larger fastener).
One advantage things like tapcons have is that a single hole size can be used through the wood and into the concrete, providing good strength against the plate moving and eliminating the need to 'spot' holes.

Shield anchors are also good.
They can use the same hole size in the wood as the concrete.


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RE: framing walls on a concrete slab with radiant heating

I agree with brickeyee that you could use tapcons to secure bottom plate to the concrete. If you are not sure where the radiant heat is and the concrete is still exposed try this.
Turn the heat in that area up so that the slab gets warm. Using a spray bottle and wet the floor around where you need to drill. The tubes will show through the moist surface.


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