How crucial are conrol joints in a 20 x 20 ft slab which will have radiant heating with in it. I’m leary about laying tubing across a control joint and are concidering to not even bother with them. Any thoughts out there???
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story

The crew discusses finding rot when remodeling, challenges installing custom shower panels, and how to prevent subs and suppliers from sabotaging builds.
Featured Video
Builder’s Advocate: An Interview With ViewrailHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Is this an exterior slab that will be exposed to the elements or is it something that is going to be framed in and insulated?
Dave
This slab will be in the interior of a new addition with no load bearing walls including the parimeter built on it. Basically it will be just floating on grade within the block perimeter.
It just depends on where you want your cracks to be.
If I understand you correctly, this slab is captured on four sides by stemwalls.
With a little preparation and attention to detail, you can probably pour a 20' by 20' slab that will not crack in the field, but just seperate at the stemwalls.
If you're past the point of subgrade prep (i.e. the tubing is down and you are ready to go), then it's just a judgement call on aesthetics. If you figure it's gonna crack somewhere, it might as well crack at the joints and make it pretty.
I'm supposing that the radiant tubing is PEX and it is tied to 6x6-10/10 remesh. If this is true, then you will have a stable situation inside that slab.
I have never worked up the nerve to try saw-cut joints over radiant. <G>
So, assuming tooled joints, guessing you would divide the floor into four equal parts, there is no reason at all for uncontrolled cracking. One joint in each direction ought to be plenty.
If you don't go with any joints and the slab does crack, it's really not a problem as long as you don't mind the appearance.
DRC
If everything is preped correctly, your tooled joints would be my first choice. The 100 sq. ft. rule works real well in his case. The biggest guestion in my mind would be the compaction under the slab. I think I would pay for the test in the case of a radiant slab. Be terrible to have it crack and settle just enough to kink a loop of that pex.
Dave
I agree 100%, Dave. Good point -- inadequate compaction could result in a very sad state of affairs.
We seem to be on a roll with compaction these days, no? <G>
DRC
What part of the country are you in.
I ask, because I know some Crosby s' in the concrete business locally. Good people.
Dave
Most of my family is in the Northeast, I broke my snow shovel and headed for the Southwest thirty years ago. <G>
DRC