Copper, PEX, Concrete and Expansion

MikeG

<span style="font-size:12pt">What happens to copper tubing and or PEX when they are embedded in concrete or other material.  As they try to expand and cannot, do they change at the molecular level?  I know that certain metals can be worked and drawn out like silver, copper iron etc.  They change and get brittle and have to be heated and relaxed to be able to work them more.  Over time will copper or PEX get brittle?  I know there are miles of both buried in concrete or other material.  I’ve torn out copper in concrete installed for 50-60 years and it still looked OK.  I’ve repaired plaster ceilings and walls that had ½” copper embedded in them.  Most of the repair was because of remodeling or other issues and not failure of the system.  These were old systems again 50-60 years.  I know they ran higher temps, but expansion didn’t seem to be the issue except where they didn’t get enough thickness over the tubing.  We did see some corrosion issues where the copper was in contact with the expanded metal lath.  Will PEX show some wear of the outer surface as it moves in the plates or hangers?  What about where PEX is installed on top of extruded foam and not totally embedded?  I know keeping the temps lower, reducing temp swings and using PEX AL will help.  No particular problem identified just trying to understand what happens.  </span>

<span style="font-size:12pt">Thanks  Mike</span>

hot_rod

same experience here

the old copper radiant systems around my area, circ 1950 were installed with soft copper tubing. It seems to be a fairly thick walled tube, maybe L or K. 3/8 OD tube running full 160- 180°F from a cast iron boiler was the installation. Makes for some warm floors, I've seen linoleum tiles squirm around on those old slabs when the heat is on for extended periods.



Around the same time a bunch of steel pipe systems were install in this area.



Failures are usually a cracked and shifted slab, or corrosion from the outside.



With the steel ones I have chopped up for leaks, the pipe rusted from the outside bottom where it was at the bottom of the pour, and lying on wet ground. I've heard of the same with copper, wet ground and cinder or fly ash in the backfill material.



I think copper, steel or pex in slab failures are mainly related to the conditions around the tube. Ideally the tube is completely encased in concrete, rarely the case. The slab and ground below is always dry, usually the case. And the sub-grade is compacted or stable so any cracks (all concrete cracks don't open up or shift and shear the tube.



I think PEX has the best chance of long term success, with a proper installation over stable ground.



hr

Solid_Fuel_Man

I believe PEX constricts slightly

The expansion is forced to go into the tube making the I.D. slightly smaller.  The polyethylene has to expand when heated and is not allowed to go outward as it would normally, so is goes into the tube.