Home Improvement Expert Danny Lipford

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How to Deal with Condensation on a Garage Floor

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Every time we have damp weather our concrete floor in the garage gets so much moisture on it that it’s dangerous to walk on. What causes this and what can we do about it? -Catherine

Hi Catherine,

There are two possibilities that can cause your garage floor to be damp:

  1. When warm, humid air comes in contact with a cold concrete slab, water vapor in the air can condense on the surface of the concrete in the same way that a glass with ice sweats in summer. This usually happens more in the spring and early summer, since the ground temperature is still low and the air is warm and humid.
  2. A vapor barrier may not have been installed under the slab when the concrete was poured. This can allow moisture from the ground to penetrate up through the concrete, resulting in damp conditions. If there are cracks in the slab and the drainage is poor, it may even cause ground water to seep up through the cracks and puddle on the floor.

To find out if the problem is caused by seepage or condensation, tape a 2’ x 2’ piece of plastic to the floor during normal conditions when the slab isn’t noticeably wet. Remove the plastic after 24 hours, and see if the concrete under it is damp. If it is, then a vapor barrier wasn’t installed under the slab when it was poured.

Do not apply a sealer or floor paint to a garage floor that doesn’t have a vapor barrier, since the finish will not adhere well to the surface. There is little you can do to correct this problem other than removing the existing slab and pouring a new one with a vapor barrier under it, or put a vapor barrier on top of the existing slab and pouring additional concrete (minimum of 3” thick) on top of it.

If the concrete under the test plastic was dry, the problem is caused by condensation from the air. To reduce the problem, you could:

  • Heat the garage during the times of year you’re experiencing a problem.
  • Rough up the surface of the concrete by applying a concrete cleaning/etching solution.
  • Apply a garage floor coating with nonslip granules or sand added to provide better traction.

Good luck with your project,

Danny

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10 Comments on “How to Deal with Condensation on a Garage Floor”

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  1. Tony Fernandez Says:
    July 21st, 2010 at 3:16 pm

    What if the condensartion is only in one area? I have what looks like a dark stain in one area and noticed moisture when I removed a bucket I had placed there. thanks

  2. linda thompson Says:
    October 13th, 2010 at 10:26 am

    I would like to raise the ceilings in my kitchen. My kitchen is very small and I think it would enhance the appearance. What difficulties would I encounter or should I say my builder encounter. Would it be expensive?

  3. Becky Hoff Says:
    April 14th, 2014 at 9:57 pm

    We had a horrible contractor, no vapor barrier under garage (motorcycle shop) concrete and we are currently in the process of repairing numerous cracks that occurred within the first month, three years ago. Can we put down garage mats over the entire floor or do we risk a moisture problem.? We are trying the plastic wrap on the floor tonight to see if their is a moisture problem. What type of flooring would you recommend to hide the cracks. Thank you.

  4. Barb Says:
    April 19th, 2014 at 8:19 am

    Thank you so much for your advice. A vapor barrier was not applied before they poured my garage floor so now I know for sure that there is nothing I can do about it. No, not going to poor another floor for sure. I have had salesmen tell me they could put a sealant on it but I just could not believe that would actually work. Now I know for sure and will just deal with it. I really appreciate your advice!!

  5. Official Comment:

    Ben Erickson Says:
    April 19th, 2014 at 9:28 pm

    Barb,
    Glad we could be of help!

  6. roseann Says:
    April 23rd, 2014 at 7:44 am

    I have had garden slabs put down for my garage floor and would like to paint them. Does the paint have to be epoxy based? If not, what kind of paint would I use?

  7. Peter Kennedy Says:
    May 30th, 2014 at 4:30 pm

    Late spring in New England, just noticed a single wet spot near garage door. I checked – it’s not coming from the car. I’m going with the condensation theory and will perform the plastic sheet check to see if the moisure is forming under or over the plastic. I do not see any significant cracks in the slab — could hairlike fractures cause actual puddling? Also, assuming it is condensation, does it make sense that the puddle would form near where there exists an opening between the garage door and the garage floor? Thanks for any input and advice. Regards.

  8. Bruce Froom Says:
    July 29th, 2014 at 7:58 am

    My non heated separate garage concrete floor gets extremely wet in high humidity. If a board or a piece of conveyor belt is lifted off the wet floor it is completely dry underneath it! How can I fix the problem?

  9. Anita Says:
    November 24th, 2014 at 2:38 pm

    I have the same problem as Catherine, when it rains my garage floor gets very wet and it is because there was not a barrier added when it was put down. I was in Lowes and they told me they did sell something that would seal the floor but was out of it. (Can’t remember the name of it now) Do you know by any chance if they have made a barrier that would work since you posted Catherine’s answer? thank you

  10. chris Says:
    November 28th, 2014 at 8:26 am

    Help! My garage floor is always wet! I bought a humidifier but it doesn’t really work. Everything in my garage is rusting, and I have noticed black mold, and green algae on the walls, and concrete slab! last weekend I took everything out of the garage and bleched the concrete! I was hoping to get some advice on this awful condition in my garage! The concrete just looks awful, and Im just ready to have a nice smooth garage floor! Thanks so much

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