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Thread: condensation outside sink

  1. #1

    Default condensation outside sink

    1st post - happy to be here - i look after (maintain) a few houses here in italy and the local plumber - while good at what he does - sometimes doesn't have a clue.

    one of our clients has condensation collecting under her kitchen sink. it never happened before and now, sometimes it does it and sometime not. it's a double, stainless steel sink with one larger and lower than the smaller one beside it. the smaller sink has a garbage disposal unit connected to it and does not attract condensation - just its larger, lower neighbor. both are contained in a wooden surround with double doors that's open at the back, against a cement plaster wall. the walls are quite thick; stone on the exterior.

    insufficient ventilation might be the cause ... but why one sink and not the other? ... why did it just start happening?

    any and all suggestions gratefully received.

    grazie - bill

  2. #2
    DIY Senior Member seaofnames's Avatar
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    There is possibly a small leak in the plumbing or no vapour barrier in the wall. Has it been raining and is this sink on the ground floor or second floor?

    Excess moisture can build up in that cabinet space and stick to anything it can. Would you happen to have a moisture meter to check the cabinets themselves and the plaster on the wall?

    Try running a dehumidifier for a few days and if that clears it up you know its a moisture issue.

    Not sure why the large sink only does it, but again, there could be a few variables in everything.

    If you could take pictures, it might help as well.

  3. #3
    In the trades Dana's Avatar
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    Quote Originally Posted by billkilpatrick View Post
    1st post - happy to be here - i look after (maintain) a few houses here in italy and the local plumber - while good at what he does - sometimes doesn't have a clue.

    one of our clients has condensation collecting under her kitchen sink. it never happened before and now, sometimes it does it and sometime not. it's a double, stainless steel sink with one larger and lower than the smaller one beside it. the smaller sink has a garbage disposal unit connected to it and does not attract condensation - just its larger, lower neighbor. both are contained in a wooden surround with double doors that's open at the back, against a cement plaster wall. the walls are quite thick; stone on the exterior.

    insufficient ventilation might be the cause ... but why one sink and not the other? ... why did it just start happening?

    any and all suggestions gratefully received.

    grazie - bill
    Too much ventilation can also create the problem. Condensation occurs when humid air come in contact with a surface that is below the dewpoint of the air. More ventilation air doesn't necessarily solve the problem- it could even make it worse during warm humid weather.

    A stainless steel sink that that recently had cold water flowing through it can end up below the dew-point of the air in the cabinet below. The garbage disposal has more mass, less surface area, and likely multlple surfaces between the water-cooled parts and the jacket/casing in contact with the air, so it's surface is less likely to be cold enough to form condensation.

    One solution would be to insulate the sink from below in an air-tight manner, so that the surface of the insulation is never below the temperature of the air under the sink and never reaches condensing temperatures. (It doesn't take much- even 3-5mm of foam insulation would do it.)

    It's possible that there is a leak in either the drain or supply plumbing (or the exterior wall is letting humidity from rainwater- cement & plaster pass humidity quite easily) increasing the humidity of the air under the sink, in which case more ventilation may temporarily reduce the problem, but it's better to find & fix the leak.

  4. #4

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    thank you both - the plumber checked the area around the drain for seepage of some sort and found none. the condensation is distributed evenly around the exterior of the bowl.

    i'll try for photos later. adding ventilation only to aggravate the situation is a worry ...

    foam insulation sounds like it might work. it's not particularly DIY friendly where we live - is there a special sort of foam needed? ... how thick? ... one with an adhesive side perhaps?

    mille grazie! - bill

  5. #5
    Plumber jimbo's Avatar
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    Foam would be hard to apply neatly. But there are a couple of other products:

    At the hardware store, you can buy 2" wide foam tape, which is meant to be wrapped aroung pipes as insulation. It is available with white outer layer, foil, or no outer layer.

    A little messy, but you could use a brush to apply a layer of Henry's 208 roof patch all over the bottom of the sink.

  6. #6
    In the trades Dana's Avatar
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    Quote Originally Posted by billkilpatrick View Post
    thank you both - the plumber checked the area around the drain for seepage of some sort and found none. the condensation is distributed evenly around the exterior of the bowl.

    i'll try for photos later. adding ventilation only to aggravate the situation is a worry ...

    foam insulation sounds like it might work. it's not particularly DIY friendly where we live - is there a special sort of foam needed? ... how thick? ... one with an adhesive side perhaps?

    mille grazie! - bill
    Molto prego!

    It doesn't have to be anything special, or very thick, just something that seals the sink surface from the surrounding air with even the tiniest bit of insulating value. Self-adhesive sheets/tapes may work, as long as the surface is smooth clean & dry when you apply it. (I'm not sure what's commonly available in Italy.)

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default sink

    unless that sink bowl was cooler than the other one, and also cooler than other metal in the area, condensation should not form on it only.

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