Replies

1. Expert Member
   BILL WICHERS | Mar 21, 2019 09:51am | #1

   If you have a few days you can wait, you can use blobs of loctite PL300 to hold the things in place. A blob on either diagonal corner is all you need, but it’s not the fastest setting adhesive.

   You could also use some very coarse threaded screws to screw into the foam to hold them in place. This works, but it’s not super secure so you can’t put much sideways force on the bolsters.

   A third option is to stitch them in place using pieces of steel wire formed into a curve like a surgeons needle, but it’s pretty time consuming to do. If have a lot of things to anchor to the foam, I’d use one of the first two options and not try to stitch things in place.

   One more idea would be to heat the bolsters enough to melt the foam a little and press them in. When the melted foam hardens the bolsters would be firmly held in place. You’ll need something that can rapidly heat the bolsters though. I’d use a resistance welding setup to do this.

   Bill

2. 
   rhl_ | Mar 21, 2019 10:08am | #2

   I’m going to try putting down the wire mesh on top of the poly+rigid, then putting tying to bolsters to the top of the wire mesh.

3. 
   Yupster | Mar 21, 2019 10:45am | #3

   Wire mesh is pretty much useless in concrete unless it's suspended in the concrete. A better method would be to use 6x6 6/6 mesh placed on TOP of the bolsters and tied in place. That will secure the bolsters and make the wire mesh perform it's function.

4. 
   Yupster | Mar 21, 2019 10:46am | #4

   Or whatever wire mesh is specced. That's just a good grade for walking on.

5. 
   rhl_ | Mar 21, 2019 10:49am | #5

   No I’m saying to secure the bolsters to the wire mesh on the floor, not to re-enforce the concrete. This would make it much easier to walk around..

1. Expert Member
   BILL WICHERS | Mar 21, 2019 01:50pm | #6

   That would certainly work. Then all you need is the cheapie steel tie wire to tie all the bolsters to the mesh.

   If possible, Use the bolsters to suspend the mesh up into the concrete too, then you get the benefits of the mesh reinforcing the slab. You can strap your radiant piping to the mesh wherever you want to get the pattern you need.

   Mesh under the concrete doesn’t do much. I can’t tell you how many times I’ve worked in commerical sites with a “6 inch thick reinforced slab” and the slab is not 6” anywhere, and the reinforcing mesh is on the bottom where it doesn’t really do anything.

   Bill

6. 
   rhl_ | Mar 22, 2019 03:24pm | #7

   I understand the mesh won’t reinforce the concrete at the bottom. However I’m much more concerned about stepping on or kinking the pex pipe, and not having floor heat. How big of a deal could not having the mesh in the middle of the pour be? Whatever your answer is, what if we add fibers to pour? Mesh tied under the slab bolsters will keep them from moving around, and will give the people more room to walk around..

7. 
   Yupster | Mar 22, 2019 03:47pm | #8

   Depends on if the engineer specced mesh or if you were just adding it for something to tie to. If it was specified, it has to go in the middle. If you just added it, it's up to you whether you want the additional crack control it provides. Seems like a waste to add mesh AND fibers.

8. Expert Member
   MALCOLM TAYLOR | Mar 22, 2019 04:04pm | #9

   Ryan,

   You are ending up with something quite odd. A soup of different metal products in your slab, all used in ways I've never seen them.

   I'd suggest backing up. What you are doing - putting down in-floor heat on top of foam - is very common. How is it usually done, and why don't you want to do it that way?

9. 
   onslow | Mar 22, 2019 04:59pm | #10

   Ryan, For what it is worth, I was faced with how to get some 1/2" pex floor heat tubing into my basement and garage slabs without risking leaks and or cracks in the concrete. I had been warned that if I tied the pex to the top of the wire mesh, then I risked having cracks appear above the tubing, especially if the pex bowed away from the mesh toward the finished surface. The concrete person had seen one job where the cracks pretty much followed the tubing everywhere. Obviously not a good outcome.

   The other risk pointed out to me was trying to fit top placed pex into a four inch slab pour. Even if I tied carefully, there would still be a risk of the relief cuts dinging one of the tubes. Ultimately, I went with three loops, two intertwined in a way that would give me partial redundancy of the main floor coverage. I placed the pex out on the foam and pinned it down with U-shaped landscapers staples. Then the crew placed the wire mesh on top and left me the weekend to tie the pex to the underside of the mesh with zip ties. My back went into retirement ahead of me, but the pex was now below the mesh not subject to leak risk from the relief cuts. The staples were used again later.

   The simple answer to raising the mesh to mid slab was putting broken bits of precast paver block that was a hair under 2" thick. No chance of pulling the mesh up too far or too low. The garage slab pour was 5" but I can't recall if I used thicker block bits. The garage also got fiber in the mix as belt and suspenders thinking. Both basement and garage are perfect, solid and uncracked after four years. As for the heat tubing, all pressure tested fine. I have not connected them as the design parameters didn't really call for heat in either location, but putting pex in as a sales feature for the theoretical next owner seemed like a good idea. My back had second thoughts.

   Trim the zip tie's tales or at least set them down to foam side so the pour goes smoothly. You won't want the tips popping up when floating the finish. The staples are pretty pricey for the Scotsmen among us, so I was glad to have the two pours set for different times which allowed me to harvest them from the first and use them to pin the garage and then finally use them to pin down the landscaping fabric under my drainage rock.

   For the thermally aware, setting the pex lower in a slab would likely increase the response time marginally, but for practical purposes it shouldn't matter. My slabs are sitting on 3" of reclaimed XPS so the heat should most definitely be radiating faster to the surface air in the basement than through the foam. Oh, and don't forget to run the pex tails through PVC elbows at the slab exit point. Don't want any dings there either.