pex and control joints

[Kaizen]

In the planning stages of a 30x36 garage. It will be a mono slab probably 6 inches thick. I would like to run pex as well for floor heat and was thinking of 3 separate loops. My question is doesn't pex risk damage if it crosses a saw cut control joint and it cracks there? I'm not talking about cutting it with a saw.
I suppose it has to if I use 10 foot square joints. Would it just squish a little? Do I not have to worry about this?

 

[sublimate]

No, I don't think so. Mine goes across the control joints.
The concrete shouldn't move much at the joint - the rebar won't let it move much so the cracks will be small.

 

[pstnbly]

You can sleeve it with PVC conduit. I did mine at the control joints, but I've seen many floors placed without sleeves and have never seen a failure after placement.

 

[Kaizen]

I have seen a lot installed on videos and no precaution was taken. Thanks for the feedback I won't worry about it

 

[Richard Cranium]

I would not worry about it, it is done all the time.

 

[matt_i]

The 1000sf slab I poured in October, 6" thick, #4 bar at 16" OC on 2" chairs was sawed the day after with the proper slab scoring tool, approx 10-12' squares, to make things look even.

There are places where the control joint could not be cut all the way to the raised wall, less the cutter wheel scar the wall.

I've been thru several freeze thaw cycles and have driven a 3000# forklift all over setting trusses.

The thing that impresses me is that I expected to see the cracks propagate past the end of the saw cut to the wall, but I can't detect a single one yet. Maybe its too early to proclaim anything, but I like what I see thus far.

I don't think there would be much problem even if the slab cracks as intended thru the control joints, the PEX is pretty ductile from what I read. The crack is shrinkage-related, so across the flat plane it will have the most shrinkage. The rebar would then keep the cracked faces aligned so one doesn't slip relative to the other like the leaning tower of Pisa which could be sort of like a shear on the OD of the soft tube.

 

[derkperk]

Being in New England where it can get quite cold, I'd run 4, 250' loops. You've got 1080sq ft so that puts you at 1000' feet of 1/2" tubing.
And like others say, don't sweat the saw cuts.


Sent from my iPhone using Tapatalk

 

[wssix99]

Do I not have to worry about this?

Yes:

Just about every PEX manufacturer will reference them in their instructions. Page #4 of this guide has some particularly good illustrations:

http://www.uponorpro.com/~/media/Ex...nual_7thEd_0711_Ch6.ashx?version=072920111126

They are needed to help relieve any stresses that might build up on the PEX when the concrete cracks along those joints. Reinforcing in the slab should keep any such cracking smaller and should also help.

 

[Tyrol67]

I used the method referenced in the instructions referenced above. About a 12" length of pipe insulation on tubes crossing the control joint. Not a lot of work. Been in 10 years now, and my slab hasn't cracked or shifted to test them, but I guess it is an insurance policy.

 

[wssix99]

but I guess it is an insurance policy.

Totally. Given what's involved in repairing a leak, this is great/cheap insurance to get.

 

[Kaizen]

yeah I can do that. definitely cheap and easy so why not? You guys are the best.

 

[joes169]

Yes:

Just about every PEX manufacturer will reference them in their instructions. Page #4 of this guide has some particularly good illustrations:

http://www.uponorpro.com/~/media/Ex...nual_7thEd_0711_Ch6.ashx?version=072920111126

They are needed to help relieve any stresses that might build up on the PEX when the concrete cracks along those joints. Reinforcing in the slab should keep any such cracking smaller and should also help.

As I mentioned in the other thread, the link you provided doesn't say you need to isolate at control joints, only construction & expansion joints, which are entirely different "animals". Zurn is the most common PEX used around here, I just looked in their book, and once again, no mention to specific directions at control joints, other than obviously not cutting through them.

I've been around concrete & heated floors long enough to see a handful of failures in the 10,000's of yards of concrete with in-floor heat, and none have been present at control joints.......

 

[rlitman]

You can sleeve it with PVC conduit. I did mine at the control joints, but I've seen many floors placed without sleeves and have never seen a failure after placement.

Rather than sleeving with PVC (which isn't going to slip onto the PEX easily), I'd sleeve with a short length of foam pipe insulation over a known joint.

If you really want to give the pipe freedom of motion, when you sleeve it, put a U bend in it, centered over where it crosses the joint.

 

[wssix99]

As I mentioned in the other thread, the link you provided doesn't say you need to isolate at control joints, only construction & expansion joints

Take another look. It says "Construction, Expansion
and Control Joints" and one of the pictures also illustrates a control joint.

I've been around concrete & heated floors long enough to see a handful of failures in the 10,000's of yards of concrete with in-floor heat, and none have been present at control joints.......

Won't it **** the first time you come across a control joint failure because a 5 cent piece of plastic was left out?

If you are using mesh to tie the tubes in place, the mesh itself is probably doing a good bit of work to counteract any stresses at these points. In itself - this added insurance is probably a good argument to use mesh to tie down the PEX tubes over some of the foam and plastic substrates that are available these days.

 

[joes169]

Take another look. It says "Construction, Expansion
and Control Joints" and one of the pictures also illustrates a control joint.





Won't it **** the first time you come across a control joint failure because a 5 cent piece of plastic was left out?

If you are using mesh to tie the tubes in place, the mesh itself is probably doing a good bit of work to counteract any stresses at these points. In itself - this added insurance is probably a good argument to use mesh to tie down the PEX tubes over some of the foam and plastic substrates that are available these days.

Here's exactly what that site says:

[Control Joints
Control joints allow the concrete
to fracture along a controlled
line. There is no concern for the
tubing penetrating beneath a cut
joint during the cracking phase
of the concrete. The concern for
the tubing is during the phase in
which the concrete is initially cut.
Depending on the depth of the
concrete, the control joint may
penetrate from 1
⁄2 inch to depths
greater than 1 inch.
Ensure that the tubing is secured
from the reach of the saw blade
and cannot be harmed. It is
recommended to secure the
tubing 6 inches on each side of
the control joint. It is important to
mark where the joint can be made
after the pour (see Figure 6-8).


How many failures have you personally seen as a result of control joints? You apparently have more hands-on experience than anyone else on this forum. I'll say it again, I've seen 10's of thousands of heated floors, and I've yet to see one fail because the tubing wasn't wrapped with pipe insulation at the control joints. PEX is far stronger than you apparently understand, which is why it is so popular in floor use. Heck, we have 60+ year old heated floors here with copper tubing that hasn't failed yet.

I understand you think it's only a few cents to install this, but it takes quite a bit of labor to lay-out joints ahead and secure the foam so it doesn't move during the pour. Money that could easily be spent better elsewhere........

 

[wssix99]

You apparently have more hands-on experience than anyone else on this forum.

I have stated nothing of the sort, nor would I ever exploit my lack of education or experience for public sympathy.

Experience is worthless currency on the internet, where everything in print "must be true." In real life, there is constructive experience, exhibited by the repeated practice of positive behaviors and there is destructive experience, reinforced by the mindless repetition of bad habits. Readers have no way to know what is what without external/third party authorities, references, pictures, or other tangible proof.

I'll say it again, I've seen 10's of thousands of heated floors

It's hard to be credible when you say stuff like that. Fortunately, math still stands up on the internet. If you worked on a new floor every day of a 50 year career, you'd just be getting to your then thousandth floor at your 50th anniversary.

I understand you think it's only a few cents to install this, but it takes quite a bit of labor to lay-out joints ahead and secure the foam so it doesn't move during the pour. Money that could easily be spent better elsewhere........

That's still not a good reason for not following the instructions. If a job is properly planned, it's a small incremental effort. If there's no planning ahead, then there is a huge incremental effort to work all that stuff out in the field -> which just devolves in to a bunch of whining, cussing, and chain smoking.

Fortunately the OP is planning ahead here and can avoid that grief!