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Thread: Black on Cold Water Line

  1. #1
    DIY Junior Member KCinToonTown's Avatar
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    Default Black on Cold Water Line

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    The picture shows three plumbing pipes that I uncovered when I tore off drywall as part of a kitchen remodel. The left pipe is the 3" drain from the second floor, the right line (next stud cavity) is hot water up to the second floor (3/4") and the middle one is COLD up to the second floor (also 3/4"). It is the cold water line that intrigues/concerns me.

    It is the only section of copper in the house that I've found with these black deposits on it.

    I've been searching the internet and it seems to get blamed on drywall or pipe imported from overseas, but given that the two pipes shown likely came from the same supply, and had the same drywall over it (sheets were installed horizontally, no seam between these two cavities) I can't accept that these could be an issue.

    I've also looked at the copper in the joist cavities in the basement and it doesn't seem to extend below the floor (difficult to see because of basement finishing), but on the second floor the bit I can see under the two closest sinks (Mstr Bath) do show the black deposits (just the cold again). The 1/2" projections to the toilets look more 'normal'.

    You may have noticed a hole in the bottom plate in the same cavity as the problem pipe. There was a plug for the fridge located just above where the picture ends (removed as cabinets are going in here). Additionally, the water supply line (self tapping valve) is installed on this line just below the floor (makes me wonder - only black deposits downstream of this self tapping valve)??

    The one other item that might be in play is that I occasionally get a whiff of sour gas smell from my sink in the Mstr Bath. I had attributed it to rotting material in the sink drain (overflow?), but now wonder if it is related to this pipe, as we don't seem to get this odour at any other sinks (relatively good water here, just a bit of hardness).

    Any suggestions? Do I need to worry?

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    I cannot see anything there that would bother me. Pure speculation, but perhaps it is caused by chemicals out-gassing from the ABS in the adjacent drain pipe.

  3. #3
    DIY Senior Member Smooky's Avatar
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    The cold pipe may have tarnished more because condensation forms on cold pipes. If the air in the wall is warmer than the water pipe condensation will form on the pipe. Warm pipes and or hot water pipes do not form condensate on the outside of the pipe. The pipe stays dry.

  4. #4
    DIY Senior Member Smooky's Avatar
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    Quote Originally Posted by KCinToonTown View Post
    I occasionally get a whiff of sour gas smell from my sink in the Mstr Bath.
    I picture from under that sink of the plumbing might help us to diagnose your problem.

  5. #5
    DIY Senior Member bluebinky's Avatar
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    The plumber may have had an old/dirty stick of copper.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Condensation on the cold water pipe. The same thing happens in basements.
    Licensed residential and commercial plumber

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