Cutting a concrete radiant slab

hot_rod · April 19

I'm adding a bath to the read of my shop space to create an ADU.

Unfortunately I needed to cut a utility trench through a slab that is only a few years old.

I do want to retain the radiant heat so I came up with a method to re-attach the cut loops.

The loops are 6" OC so it required a number of couplings, and some concrete sawing.

These 12" electric hand concrete saws work amazingly well. I used a gas powered walk behind sam for them long cuts. The hand saw was just as fast to cut, actually.

I used the wet saw to cut parallel to the loops first. Then a cut across the tube about 1-1-2" deep. The piece came out easily with a chisel. Luckily concrete doesn't stick to pex, so the tube was undamaged to reconnect. This provided just enough room to get a crimp tool around the tube.

I can slide some insulation below the tubes, some rebar to keep the pour stable.

EBEBRATT-Ed · April 19

Looks like a LOT of work.

No pressure test needed LOL!!!

ScottSecor · April 19

My back and knees are hurting just looking at your project. Unusual cuts in the slab.

Are you at all concerned with not being able to re-tamp the soil and stone under the new pex? Do you plan on "connecting" the two slabs with rebar before pouring your new concrete?

As usual with your projects, there will be no corners cut. Thank you for sharing the photos.

pedmec · April 19

Maybe its the pic but those pex lines look pretty deep in the slab. Looks like they are on the bottom of the slab.

Alan (California Radiant) Forbes · April 19

I would have trusted Uponor’s joining method more than crimp rings. Also, less pressure drop when you add up all those splices, no?

hot_rod · April 20

https://forum.heatinghelp.com/discussion/comment/1894687#Comment_1894687

I thought I had done a better job of suspending the mesh on 2” foam blocks You learn a lot when you cut into a slab 🫢

It is 6” oc, and I run constant circulation, and ODR, so it maintains an even room temperature

hot_rod · April 20

I did get to un disturbed ground to put in the sewer line, I wet the back fill to help settle it

Not a bad idea to pin it across with some rebar drilled into both sides

hot_rod · April 20

https://forum.heatinghelp.com/discussion/comment/1894694#Comment_1894694

The black pex is Viega B pex, I didn’t want to expand that

I looked for a crimp x expansion coupling as the red pex is Mr Pex, A pex

psb75 · April 20

Wow. Just…Wow.

Alan (California Radiant) Forbes · April 20

I like these Viega PureFlow couplings for non-PEX A tubing. (Thank you @kcopp.)

PC7060 · April 21

Hat off to you @hot_rod!

I don’t have your experience with or appetite for cutting into a hydronic floor assembly like that.
I think I’d gone for a macerator pit with pump to route the waste line over the or around the living space. Could you have routed the sewer in trench around foundation?

hot_rod · April 21

https://forum.heatinghelp.com/discussion/comment/1894765#Comment_1894765

I looked st sll the options fir routing and the line does run to an ejector pump located in the shop that is connected to this space . I looked at an over the top product also, but height is tight.

The cutting was easier than I thought, took about an hour and 1/2

Splicing and crimping took a lot longer

It was as much about the challenge as the destination.

Loop flow is under 1/2 gpm, so the 80 couplings are not too much of a restriction to flow

nate379 · April 21

Around here 12" spacing seems to be common.

I have a bathroom add on to do, ideally would be able to bust the floor up to run piping, as I'm limited on height, but likely will do a false floor.

hot_rod · April 21

The closer spacing give you more consistent slab temperature, good for baths to use 6". You feel a wide temperature spread wit 12" min bare feet.

It also gives you higher btu/ ft output, quickens response and allows for lowest supply temperature. I run an A2WHP so low temperatures drive the HP efficiency up.

The depth of the tube matters also. I had thought I did a better job getting the tube 2" below by raising the mesh on foam blocks. You really need to use continuous bar chairs every 2' to assure the mesh stays up into the pour. That adds a lot of steel cost.

Tube 6" OC and into the slab can drop your supply 10 degrees or more. See below charts.

For my own slabs I always do 6" oc. It can be done with 1/2" pex if you light bulb the ends.

This slab as poured several years ago.

PC7060 · April 21

https://forum.heatinghelp.com/discussion/comment/1894782#Comment_1894782

wow, 1.5 hr is not bad; hauling it away probably took that long.

If i did that many joints, 1/3rd would leak! 🤣

GroundUp · April 22

I sure hope you wrapped those brass couplings and copper rings with something to keep the concrete off of them….. Even electrical tape does wonders, but I switched to poly couplings and SS collars a few years ago after repairing a few of my old repairs that were not wrapped. And still wrap those joints.

Cutting a concrete radiant slab

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