I'm in the process of tearing out carpet and installing laminate in my guest bedroom. After I got the carpet out, I discovered a hole several inches across underneath the wall that borders the garage. The other wall, which is a foot or so away, is an exterior wall. In the center of the hole is a copper pipe (~1/2" diameter) with pipe insulation around it.

I THINK it runs outside to my A/C unit, but I'm not sure why it's running into the slab, since the line for the A/C exits a few inches up the brick. The evaporator is in the attic.

Can I just fill in the void with concrete patch? Do I need to wrap the pipe with anything first?

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  • Good question, yes you can fill it in and should. You should also consider covering the copper pipe with something as I have heard concrete and copper don't get along after many years. Dec 30, 2014 at 21:59

2 Answers 2


Bare copper will eventually corrode if it is in left in direct contact with concrete over time.

You can try wrapping the pipe in duct tape and then covering it with sand, then skim coating over the top with concrete. That way, you could get access to the pipe again if you needed to.

  • This is essentially what I ended up doing. I put a few turns of duct tape around the pipe first. Then I mixed up some Quikrete concrete patch and filled the hole. Unfortunately (fortunately?) the Quikrete didn't set right even though I mixed it the specified ratio. It was more of a hard packed sand/grout texture than concrete. I scraped the loose bits away and covered it with the Quikrete Polymer patch compound I was using for filling in the craters from the tack strips.
    – Doresoom
    Jan 5, 2015 at 21:19
  • @Doresoom That shouldn't be an issue. It looks like most of the pipe is already embedded in concrete anyway. You could have also used mortar mix as well because it doesn't get quite as hard as concrete, and you could chip it away with a cold chisel. Jan 5, 2015 at 21:23

I would definitely not fill it with concrete until you know what function the pipe has. If you think that it will affect your flooring installation (it might), I would use a more easily removed material to fill the void. Good luck removing a concrete patch without destroying the pipe if for some reason you needed in there someday.

Some flooring leveling materials form a sort of rubbery material. If you had to remove that material someday, you would have a much better chance of removing it than concrete. I've used such materials to fill voids in concrete slabs to support laminate flooring.

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