I'm installing a new vanity and found green oxidation at the elbow joints of the copper pipes exiting the wall. As you can see in the pictures below, there is much more oxidation on the hot water pipe (first two pics) than the cold water pipe (third pic).

I recently purchased the home and don't know the history of this plumbing. Nor do I know much about plumbing, but it looks to me like the soldering on the joints may be newer than the oxidation. If so, perhaps those joints were previously leaking and then repaired, so nothing more than perhaps a good cleaning is in order?

Or does the amount of patina suggest that I need to remove/replace one or both pipe sections?

Thanks in advance for any help.

hot water pipe A hot water pipe B cold water pipe

3 Answers 3


Solder flux will cause copper pipes to turn green if not wiped off.

The discoloration is limited to areas bordering soldered joints, so it is almost certainly caused by the flux not being wiped off back when the connections were originally soldered.

It should be limited to surface discoloration, so I'd use something abrasive like emery cloth or steel wool to remove it.

  • Just plain water and a wire brush should remove any remaining flux. Many copper corrosion compounds are green/blue; not worth trying to figure what they are . Commented Sep 7, 2021 at 16:44
  • Thanks for this. Sandpaper took care of it.
    – Rich
    Commented Sep 15, 2021 at 22:57

I would start out by cleaning up the pipes with a mixture of vinegar and baking soda into a paste and coating the area where the patina is present. Leave the "paste" on for 10 minutes and wipe off. Dry the pipe completely. Then monitor the situation and look for more patina and/or any leaking. This could very well be an old problem that was fixed but not cleaned up.


"Oxidation (turns green or dark black) is common on copper when it is exposed to water and air over time. While this oxidized layer is not harmful, it does cause the copper to become corroded. This green color (patina) is known as copper oxide and is basically a rusting of the metal."

You shall consult with a plumber to address the root problem and replacement.


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