Soldering, Unjoining, and Resoldering Copper???

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by jjohanson, Feb 16, 2009.

  1. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Question 1:
    Can I use a compression fitting over solder leftover from a prior solder joint?

    Question 2:
    Can I re-solder a joint after heating up the old joint, removing the old fitting, and briefly cleaning the old solder with a wire cleaner?

    Background:
    I am new to sweating pipe - I have read up on proper pipe cleaning and soldering techniques, but have not found that much information on how much you can work with a joint that has already been soldered.

    For example, I have one scenario where there is an existing 3/4" copper stub-out for a shower faucet which has compression fittings. The 3/4" copper has caps which have been soldered on. Can I heat this up, remove the caps, and simply attach the compression fitting over where the cap was (after a brief cleanup with a wire cleaner to generally smooth the solder out)? After running the wire cleaner over it for 1-2 minutes, it is not getting through the old solder and down to the copper.

    Related example, if I want to redo a solder joint and I remove the old joint per above, can I just place new flux over the cleaned solder joint and re-solder a new fitting on?

    [​IMG]
    Soldered with No-Lead solder
    Last edited by a moderator: Apr 7, 2009
  2. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,395
    Location:
    Yakima WA
    I have never attempted using a compression fitting over a previously soldered pipe, but my guess is that if you heat the pipe then wipe the residue solder well, as long as the compression ring will slide on the pipe, it should be OK. If this is incorrect, I'm sure some of the pros will correct this. Redoing any old joint, the key is getting the old solder off it pipe, (as described above) and cleaning the solder out of the fitting. The real problem is getting the old fitting cleaned out well enough to get the joint reassembled. I think most of us find that trying to reuse a fitting is not worth the small cost of a new fitting, but it can be done. Other than the cleaning the old solder, treat it like any other joint.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,313
    Location:
    New England
    Some people pay extra for pre-tinned fittings! As long as the pieces are cleaned of gunk, you add flux, and you can get the fitting over the pipe, it's no big deal to solder it back together. Sandpaper or a bastard file will get the excess solder off, but heating it until molten then wiping with a clean lint-free rag will be faster and easier.
  4. dx

    dx General Contractor

    Messages:
    156
    Location:
    Michigan
    Q1: No.
    Q2: Yes.
  5. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Thanks for the responses!

    After Gary and Jadnashua's posts, I tried to pull a fitting and re-solder - worked well. I was having trouble before because I had not reheated and wiped the old solder from the pipe.

    DX,
    Can you give a reason for the "no" on this one?
    Assuming I cleaned the old solder off and sanded down, what would be the issue?
  6. kingsotall

    kingsotall Plunger/TurdPuncher

    Did you get the caps off¿
  7. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    kingsotall,
    not yet, I plan to do that this morning on a fresh start.
    i'm going to give them a good clean and give the compression fittings a shot.
    the only potential issue I see is that after the pipe is sanded/cleaned, there is a sanded "texture" left over, which the solder would typically fill; I hope the compression fitting is tight enough to seal over this.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    joint

    If you heat the pipe and wipe the excess solder off, (there will still be a thin layer of solder on the pipe however), you can use a compression fitting on it. And once the excess solder is wiped off, you can also reuse it for a solder joint.
  9. kingsotall

    kingsotall Plunger/TurdPuncher

    Before you apply heat, drill a pilot hole into each cap to be removed drive a screw in and then pull on the screw with a pliers as you heat the joint. This saves a lot of headache. As a test try this on one cap and then try just pulling on the cap without a screw drilled into it.
  10. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Kingsotall,

    Good suggestions.

    I drilled two holes in each cap to make sure that any steam had a place to escape in the off change I somehow hadn't cleared all the water. I read your post after that, so didn't leave a screw in to pull the cap off. Actually this was an issue because I couldnt seem to get the solder to give, and the copper was heated to a point that when I used the pliers, it crushed a bit.

    I cleared as much water as I could using the drippers lower in the system and blowing through the holes in the caps, but there was still some sizzling sound from the pipes.

    Any tips on what to do if the solder wouldnt give, but the copper became malleable? Is this an issue of water still in the pipes?

    I am using a Bernzomatic propane torch, heating the cap with the tip of the sharper flame.
  11. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    Also, is it possible to overheat the piping to the point it is no longer good? What would be some signs that this is happening?
  12. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    An update...

    I couldn't get the caps off at all - the solder just wouldn't loosen, but the copper was so hot that it would warp when gripped with pliers. I tried putting screws in the caps, but they would pull from the copper.

    I just cut down the pipe further in and re-soldered a new length of pipe on the end. Worked fine.
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,242
    Location:
    Cave Creek, Arizona
    caps

    The problem is usually that you cannot get a grip on the caps without damaging the copper, and that is why they did not come off. By the time the copper is hot enough to deform, the solder joint has been "free" for a long time.
  14. jjohanson

    jjohanson New Member

    Messages:
    15
    Location:
    New York
    HJ, Thanks for the input.
    I'd imagine once I deformed the copper, then the cap was mechanically locked in place,and it was game over.
  15. drrjackson

    drrjackson New Member

    Messages:
    1
    Location:
    Toronto
    Great thread. Thanks everyone.
  16. Gary Swart

    Gary Swart In the Trades

    Messages:
    7,395
    Location:
    Yakima WA
    This is a pretty old thread, but no one has really addressed the issue of water in pipes, While there are often more than one way to do somethings, one basic principle that can not be violated. You can not sweat copper if there is any water or moisture in the pipe. The torch heat will generate steam and since you can not heat water above 212 degrees, you can never get the pipe/joint hot enough for solder to flow. This is true whether trying to sweat a new joint or unsolder an old one.
  17. jeffeverde

    jeffeverde Member

    Messages:
    80
    Location:
    L.A.
    If you're capping a stub for future use, leave it long enough that you can cut the cap off rather than "unsweating" it -- especially if it's at a low point where you're likely to have trouble draining the lines.
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