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Radiant Slab Install

Radiant Slab Install

Radiant Slab Install

I am building a 33 ft x 31 ft. garage with a radiant slab. The sandwich will be 4” washed stone, vapor barrier, 2” foam, radiant tubing stapled to the foam, 6x6 WWF on top and maybe a rebar grid on some chairs and 4-5” of concrete. Based on the layout of the doors, it would be nice to break the slab up into 6 chunks of 11 ft x 15.5 ft.
My question involves control joints. I am going to epoxy coat the slab if it makes any difference in your answers. I will also discontinue the WWF and rebar at the joints. I am concerned about using a soft-cut saw as it may hit a line if they are not careful. I have used keyway on previous slabs and it worked ok but the concrete starting chipping adjacent to it. I have also done two checkerboard pours that worked amazingly well but I don’t know that I want the expense of that on this project as I need to rent a pump twice and the labor basically doubles. My other thought is to use tooled joints but don’t have too much experience with them other than I always see cracks running adjacent to them in tract homes. Maybe if they did a 2” deep joint, that would be more effective. Is that even possible? I welcome your thoughts and ideas. My other question involves the safety of the piping during the concrete placement. Will the WWF somehow puncture the tubing with all the workers scurrying around on top of it? I have heard a few isolated cases of that.


RE: Radiant Slab Install

XR - if you're going to use rebar, why do you have WWR in there, too?

I typically spec saw cut crack control joints. When the concrete is just firm enough to take the saw without tearing out aggregate - about 6 to 12 hours, but closer to 6 - they run the saw with the blade set to 1" for a 4" slab on grade. It takes careful coordination to make sure the cut lines up with the interrupted reinforcement (wire or bars). But this would protect your tubing as long as they keep the depth of the kerf locked in.

I don't have any experience with tooled joints - most of the contractors around here seem to prefer saw cutting - but the tract homes I've seen with the problem you mention is usually due to cuts happening a day or more after the slab has been poured. The damage is done by then, and it just takes a bit more time for the cracks that had already formed to open up and become visible. That's if they joint the slab at all. A lot of the cheap developers just don't bother - let it crack and cover it with carpet/laminate flooring.

RE: Radiant Slab Install

The WWF is there to keep the tubing down. The staples like to pull out of the foam and the tubing wants to float.
Good point on the cutting. I could be pretty generous with the tubing and rebar space near the cut.


RE: Radiant Slab Install

Another issue is the concrete guy does not like admixtures and this will be placed in January so it may not cure fast enough for him to cut unless he brings a sleeping bag.

RE: Radiant Slab Install

If you’re worried then you could always use a zip strip instead of saw cutting it.

RE: Radiant Slab Install

Ahh, never seen those before - pretty cool.

RE: Radiant Slab Install

Just a word of warning - ACI 360 recommends NOT using plastic inserts to form crack control joints in slabs with wheel traffic. My guess is that while it forms a nice weak plane, it probably disengages the aggregate on either side of the crack too much to provide any sort of post-crack shear friction/aggregate interlock to keep the surfaces flush as large point loads roll over the joint. For a garage, you might be able to avoid it by keeping the zip strips parallel to the direction of traffic or including smooth dowels placed just below the bottom of the strips if you're going to have a pull through.

As for timing early entry saw cuts...maybe a late night pour and an early morning saw cut? Or an early morning pour with heaters and blankets. The latter is probably better.

RE: Radiant Slab Install

If using WWF for the bottom, and place your reinforcing 1-1/2" from the top, why not sawcut... and at the right time. Zip strips work, too.

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RE: Radiant Slab Install

After discussing this with my concrete sub and honoring his skill set and tools, I think I’m gonna end up doing keyway. Thanks for all the advice!

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