Pex frozen in concrete slab of new home

Tom_35

We started piping making final connections on a job Wednesday and when we pressurzed the system with water, we started seeing water coming up through the slab in different areas.

We tracked down the areas where the water was coming up through the floor and chipped the concrete up to find where the pex had evidently froze and burst. We had Watts copper manifolds that were located in different areas of the home (which is still open to the weather), and there was no problem with the manifolds rupturing.

We've never had a pex pipe freeze before, and this winter has been relatively mild as compared to others, where we have never had a hitch. The coldest temperature we've seen this years has been in the upper teens, and that was just for a day or so. I realize that is plenty of time for something to freeze, but we've had prolonged temps in the past that have been in that area and haven't seen any problems.

The only difference between this job and the others was that Insul-tarp was used in lieu of the foam board insulation. The job was supposed to have the foam board, but the GC filled the interior with too much gravel and didn't want to take it out. The result was going with the Insul-tarp, which I have since learned on The Wall that is probably not the best choice.

None of the floor is below grade. Do you think that the fact that the temperature of the gravel fill allowed the cold to get through the tarp, since one of their claims is that it reflects the heat back up to the floor, thus not acting as a good insulator from the floor up?

I've seen many posts here where pex has been frozen and never burst. Why didn't the copper manifold burst?

Thanks for you input.

Tom A

Weezbo

Tom....

in cold weather ask the owner first if he wants to put anti freeze in the system...if he says no then say ok ..well pay me and i will leave it as it is,here and now. When garage doors dont meet the floor and or the door is left open or wont or cant be closed........even anti freezed doesnt mean it wont eventually lose against the cold.no reason to leave pressure at 100psi all day and night either. once the test is over drop the pressure.to like 60 psi. the go pro ultra sound machine is a handy gizmo for determining leaks ....did you have some eyes on the job during the pour?

hr

I suspect the insulation worked against you

in this case. It prevented any warmth in the ground from protecting the pex in the slab. So the entire slab, including the bottom where the pex is located was exposed to the below freezing temperature.

Although at some point, with extended below freezing temperatures, the freeze up was inevitable.

The 1" foam may have in fact sped up the process

Maybe there was some air pockets in the manifolds at the high points that saved them?

Personally I feel pex encased in concrete has less ability to handle freezing and the expansion room it needs to prevent bursting. I have seen exposed PB and pex swell up to handle the freeze expansion, and not rupture.

Curious why it had water in to begin with. Job schedule fall behind?

regardless of the time of year we only air test now. I've had some cold experiences trying to blow water tests out of pex lines. Pretty hard to get every single drop out, and you end up with low pockets of freeze sections. Like trying to thaw a frozen garden hose.

Besides the sections you have uncovered you could have some pretty "stressed" pex in other areas of that slab

hot rod

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Dave H_2

Burst and frozen pex

Tom-
Main reason the pex burst in the slab and not at the exposed areas (copper manifold and such), is that the tubing doesn't typically burst where the ice is.

When ice is created it takes up more space that water. As the ice grows, it starts to exert pressure on the water that is still in the pex. Since water is incompressible, the pressure exerted onto the pex is extremely high.

So, at your burst points, there was water and at the supply and return parts of the loops was frozen pushing the water in the middle.

Wayco Wayne_2

I only test

with air since a tubing run I had freeze overnight had 5 bursts in a slab. It was an early unexpected freeze but after finding so many holes we decided to tear up the slab and re-run the pex with new. I think it was the only time I ever used my insurance. I had gone to a seminar where a pex manufacturer had espoused the hardyness of pex when water freezes in it. I called up and asked whazzup and they said freeze resistant, not freeze proof. D'oh! WW

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Tom_35

Thanks for the replies

hot rod, you're right---the job did fall way behind in construction.

We put water on it before the slab was poured. When the finishers were cutting some expansion joints in it, they cut way too deep and cut a pipe. We repaired it and left water on it and asked them to please cut very shallow slots from that point on--which they did. They figured they would have everything in the dry by mid-November and need heat. Since they've still don't have it sealed and insulated, they are missing it by 3-4 months.

Everything is holding pressure now and we are holding our breath as well. Absolutely make me anxious about the "stressing" of the pex though.

We all live and learn in this business. Will keep you posted on how this pans out.

Tom

hr

I've been down that exact road

I did try to blow the water out, on one job, it must have had some pockets remaining as some loops took a long time to open up when we finally dumped heat to it.

Takes a mighty compressor to get all the water out of several thousand feet of tube. Maybe a large CFM type like the lawn sprinkler guys use.

If it holds high pressure now, the 10- 20 psi it will see under heating use should hold just fine.

Fingers crossed.

hot rod

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