What is a good and secure method to have control joints made in concrete that was poured over PEX tubes for radiant floor heating? How can we exclude any damage to the tubes when the joints are sawn in the concrete? Or is there another method to do it? Slab will typically be 4" thick. We (Owner Builder) are in Arizona where contractors are not used to work with under slab heating. We try to save money and lay the tubes ourselves. But we do it first time. Any helpful comment is appreciated.

Rafi - how are securing the pex?

Does it have to be saw cut? I just let it crack. If you are staining and polishing, it looks even better with the cracks.
Alternatively, you could tool the joints or lay in expansion strips.

Rafi - how are securing the pex?

We will zip tie the tubes to the mesh.

Does it have to be saw cut? I just let it crack. If you are staining and polishing, it looks even better with the cracks. Alternatively, you could tool the joints or lay in expansion strips.

Thank you. I will forward your suggested options to our possible concrete contractor(s).

If you plan to use control breaks, Siegenthaler best practices are to sleeve the PEX and keep the PEX lower in these areas. The concern here is that any time a significant crack and concrete separation occurs, this can stretch and damage the PEX. If your PEX is tied to rebar, you are less likely to experience a significant crack or concrete separation even if you do not use control breaks. If your PEX is tied to WWF (welded wire fabric), you are more likely to experience a significant crack and concrete separation if you don't properly place control breaks. So what you do really depends on how you plan to execute it.

Rafi - the simplest way to deal with cracking is to use crack inducers. Install a 1" x 1" sheet metal angle (available from drywall suppliers) and place it at the bottom of the slab with one leg up. Then lay rebar over the crack inducers and tie the pex to the rebar. Bear in mind that the metal angle can have sharp edges so you want to watch the pex placement. To avoid damaging the pex you can also lay the angle with both legs down to make a 45º crack inducer.

Mark the locations of the crack inducers and when the concrete has been finished, take a diamond blade in a circular saw and cut a 1/4", groove over each crack inducer. This will help keep the cracks straight and neat.

If you use 4" of 30 Mpa concrete with 10m bar at 18" o/c and poly fibres over properly prepped underslab or foam and you keep the slab all at the same thickness, it has little likelihood of cracking.

Unless you are using a commercial grade w.w.m. you are wasting your money. Just use rebar.

That's a good thought FBBP. How well do sheet metal angles actually work in practice for supporting rebar? I think they would be somewhat unstable and flop over under the weight of the rebar. I think an inverted "T" section that had rebar grooves at the appropriate spacing and placed the rebar in the middle of the slab would be perfect and would be a great product. Agreed, don't confuse WWM with WWF.

I would not use the angles as support other then where the control joint happens to coincide with the requirement of support. If you put in enough to support bar, the slab will crack into many small segments.

Of course I prefer to use the pex to support the rebar ;-)

Yes, I am only too aware of your PEX location preference and given where you operate and the associated need to use several inches of under-slab insulation, I am not even too offended by it anymore as the performance hit is not nearly as significant as where we operate ;-)

Okay, so maybe it is actually my thought…place a grid of “concrete crack inducers” where the control breaks are desired that are capable of supporting the rebar/PEX at mid-slab height in those locations. We often place concrete control breaks directly below where the interior walls will be placed (and where PEX will NOT be placed) so as to conceal these control breaks. It would be great if we could avoid having to accomplish deep control break cuts if this “concrete crack inducer” concept works well.

Sailor - we did a large mini storage unit last year. It was a big U-shaped building but the depth of the building was only 14' to 18' deep depending on sides or ends. As the individual units where to be 8 to twelve feet wide, I laid an inducer under every second demising wall.
All the cracks showed up on schedule between two and four days after the pour. (shrink cracks)

Now here is what really ticked me off. Had a knowitall plumber hire by the owner who installed the radiant. Boilers where at both ends of the U which necessitated manifolds near the bottom of the U to meet flow demands. Buddy lays up his loops as needed , tying them to my bar, then lays his 1" supply lines OVER TOP of the 1/2" in the 4" slab.

Client now has very neat control cracks under his walls and an "as the crow flies" pair of cracks running longitudinal between the boiler rooms and his manifolds.

Thank you FBBP, this crack inducer approach sounds perfect and I fully expect we will use it soon. We have a fabrication shop that does our water work project fabrication (e.g., water wheels, cross flow turbines, etc.) and we will have them fabricate some sheet metal “T” sections as I described previously. We have never liked having to keep the PEX low in the control joint areas and incurring ANY risk of cutting the PEX when creating the required control breaks. This is really quite a cool approach and it has been a while since I have been so excited about a implementing a new construction process improvement for our operation.

With regard to your plumber, at least he was hired by the owner and was NOT one of your sub contractors. Yes, I know exactly what you mean and it always frustrates me to no end when some bonehead does something dumb like that.

Most radiant floor PEX tubing is stapled directly and correctly to rigid insulation, wire laid over and the slab poured with 1" saw cuts made without worry. Where we specify a raised tube, rare, and have been using Zip strips for over 10 years now, but they are hard to keep straight and unnecessary except in an occasional basement where saw cutting is impractical.

We do not suffer from "no-it-all" plumbers because we do not try to confuse them with tube placement. And we are licensed plumbers, among other things.

If you do raise the tube in the slab know that Manual 'J' has your winter outdoor design temperature at 24­°F and your earth temperature at 67° i.e. there is nothing to be gained.

Precisely and this again further illustrates why plumbers doing crude Manual ‘J’ analysis have no business designing HR floor heating systems.