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Gravel on Copper Radiant pipes

Jay1970 Member Posts: 1
Hi - we have a 1950s Eichler house in North California. Copper radiant pipes embeded in concrete. Everything works fine and beautifully. Just got some remodeling done and because of that we had to excavate the manifold area (and break all pipes in process). Everything has been repaired now with a great new manifold and system has been tested etc. Getting ready to pour new cement over the excavated area (about 3 Ft by 6 Ft). QUESTION: Which option is better:

Option 1: Fill dirt up to 1 inch below the radiant pipes, put in 2 inches of gravel on top of dirt so that copper pipes are 1 inch BELOW gravel, pour cement on top of gravel.

Option 2: Fill dirt up to radiant pipes (but not covering the pipes, pour cement on top of pipes (so that pipes will actually be embedded in concrete)?

Also if Option 1, what gravel will be best?



  • Zman
    Zman Member Posts: 7,467
    Pipe Insulation

    You do not want your copper pipes to come in contact with concrete.The fly ash in today's concrete will eat your pipes. If you do not intend to have heat in the area you have demoed, just wrap the entire pipe with insulation. If you are heating the area, the horizontal tubes could be taped and the vertical tubes insulated. This will also help isolate the pipes from settling and expansion.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • McMaster
    McMaster Member Posts: 28

    I recently had a conversation with an engineer who was telling me how he built his radiant system before reliable PEX was available. He put his copper under the slab (above insulation). He had researched it pretty heavily before ending up with a game plan. I believe he said he put gravel or washed rock above the pipes and cement over them. It's been working great for over 20 years. I'll ask him again what rock he used and report back when I get an answer. 

    I know of a Frank Lloyd Wright building where they also did this many, many years ago. Unfortunately, I don't know the specific details of how they did the copper pipes or concrete. It lasted for a good 50-60 years, but has been developing leaks in the last 10 years or so. But the point is, it's been done a bunch of times. Sorry, I can't offer you any more than that.
  • RobG
    RobG Member Posts: 1,850
  • MikeG
    MikeG Member Posts: 169
    Copper and Gravel

    I can't speak to the longevity yet, but I have 60' of soft copper buired in gravel under a concrete slab.  In my area, NW Ohio we have a lot of limestone quarries.  I used what we call screenings, crushed rock with a lot of fines. Biggest pieces maybe 1/4"-1/2".  It packs like concrete and we use it a lot for driveways and under concrete for a base.  I did this in a utility room, 2" of extruded foam under and around perimeter, 4-5" of gravel and 4" of concrete.  Itried to keep the copper centered in the gravel.  I am concerened about the expansion movement eventually causing pinholes. Did some of the concrete slurry seep into the gravel and will that react  with the copper, who knows.  I run 110-112 degree water through it and it works fine for now.  I installed it 1985 with no heatloss or design.  It was capped off and I didn't hook it into the new boiler untill 2010.  I've plumbed a bypass if I have to abandone it, and am going to install radiant ceiling hopefully this winter.  As others have posted I would bury in soil, or isolate.  I have dug up copper water lines from soil, sand and gravelly mix etc.  They were still working but who knows.  Just some thoughts.   Mike
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