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Question DetailsAsked on 5/4/2017

Unexplained water on garage floor on hot day

New owner of a house, it's a finished garage, Its been raining a lot, but last two days have been hot.. why does the floor sweat? Water isn't on anything else.. please advise

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2 Answers


Check for internal sources first of course - leaking overhead pipe, water (or antifreeze or air conditioner condensate or even overturned liquid cargo) dripping from a car, water /sewer pipe leaking in wall and running onto the floor, condensate or leakage from any appliances, leaking air conditioner coil condensate collection pan or blocked/broken drain line, water heater or boiler overtemp/overpressure valve leaking or blowing down.

And pets wetting the floor (they tend to use the same spot once they find one where they do not get yelled at - do you have housebound pets in the daytime or night ?).

And of course kids working on construction projects or firefighting or boat floating play or such.

If you have narrowed down to leakage from below, then could be broken pipe in the slab (should probably be able to hear hissing over the break if a water pipe, putting ear to concrete).

If very humid and hot, if humidity in garage is very high you could be getting moist ground under the concrete wetting the bottom of the concrete, and it is wicking through the concrete to evaporate a the surface, but cannot evaporate because of the high humidity, so you get condensation - usually will be spotty and droplets around the edge of the pool rather than just a pool.

Otherwise, high ground water or leakage from roof runoff or such coming up through the slab - look at outside ground elevation to see if that is a possibility. LOTS of previous questions about concrete slab and foundation (usually basement, granted) leakage can be found in the Home > Basement Waterproofing link under Browse Projects, at lower left - some of which also have checklists of causes and solutions.

Consider also if could be water that came through/under garage door or window or such.

If generally sweating over much of the floor (especially if finished floor) and air humidity is high, could just be condensation of moisture from the air on the much colder floor. COuld also be ditto except the moisture is coming from the foundation walls if they are wet on the outside - evaporating to the air, then condensing on cold floor. You can get cheap (under $10) humidity gages to check air humidity to see if coming from the air or (if air humidity is below about 80% close above slab) maybe water vapor coming directly through the slab because the vapor pressure is lower in the air above (hot, dry conditions) but then condensing on the cold slab - same mechanism as where you get condensation and sometimes even frost on metal and plastic/glass on clear nights in the desert even though the daytime air is hot and dry feeling.

Here are links to a few previous similar questions with answers specifically about wet garage floors:

Answered 3 years ago by LCD


Answered 3 years ago by LCD

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