How to Deal with Condensation on a Garage Floor

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,


Further Information


  1. 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. 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. 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. 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. 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?

  6. 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.

  7. 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?

  8. 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

  9. 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

  10. i recently apply the Home Depot epoxy floor kit to my garage floor. After about 3 weeks I am noticing that the floor is damp and wet in various areas, any ideas what is causing this or what I can do to prevent this moisture? Thank you

  11. I have some metal storage buildings. some of the units gets wet when the humidity is very high. If there was no moisture barrier under concrete when concrete was poured,do they make a sealer I can use

  12. i put up a metal building. Put down a vapor barrier before pouring the concrete. Sealed the concrete. Had spray foam insulation installed. My car is always covered with condensation. How can I cure this problem!!
    Thanks Greg

  13. My garage has been collecting puddles of water after the recent rains we have had. Can I assume that the same thing is probably happening under the carpet in the rooms that are connected? And if so how do I fix this to prevent mold?

  14. I’ve just had a small extension put on the back of my garage. I believe a damp-proof sheet was used under the concrete floor as indicated by the telltale black sheeting used before the concrete floor was poured. I’m guessing that this sheeting is the vapour barrier you talk about. After the construction was finished I painted the concrete floor in the new extension. All seemed good and it dried well. However, whenever I place a nonporous item on the floor the paint after a couple of days seems to become wet (possibly separate) with a strange green colour. The rest of the painted floor is dry. I never had this problem with the original part of the garage when I painted it. Any ideas?

  15. My garage floor has condensation, especially when it is muggy outdoors. Even if the floor is dry, anything on the floor is damp underneath the item. When a nail was hammered about 2 inches into the concrete in the garage it was dry. It’s only on the top that the condensation forms and not all the time. I could go days with a completely dry garage and then the weather changes and the entire garage is wet. i don’t know if a fan would help or some kind of paint would help. Pleas advise thank you

  16. We built out house 1991. In our garage these last few months has been a pool of water…. At first we thought it was from a variety of boxes, coolers etc. so we moved EVERYTHING away from the area that pools water. We have dried the area off completely dozens of times… continually pools back up. The pool of water is not in the center of the garage or near any water pipes, sprinkler systems or ANYTHING associated with water. None of the surrounding walls or ceiling of our garage show any signs of water damage. It does have a sort of dried 2′ stream to where the 12″-16″ pool of water collects. The entire pool area with the stream is at least 6′ from any of the walls of our garage. We are dumbfounded. Our garage is enclosed with a garage door that is always closed except we do leave 6″ open for our cat.
    Any ideas?

  17. We were getting a new floor down, then when the floor layer came, he lifted a piece of the floor and told us that the concrete floor was wet and he couldn’t put it down, so he got us dehumidifiers to dry it out. Then the water board came out and discovered there was a leak in the house next door to us. The house is empty but people still own it and come back and forth to it. Anyway the water has come through into our house.

    Then we got and builder out who told us the floor was dry and he took about 14 inches of plaster off and right down to the brickwork of the party wall and replastered the whole wall. The floor layer was out and told us the floor was still damp and he could not put the new floor down until it was dry. Who do we believe the builder or the floor layer?.

    Any advice on how to tell if the floor still is really damp? Now the builder inspected the floor, it has been done right he told us, so he used his damp meter and there was no readings of damp yet the floor layer is saying it is. The floor has been done right because the builder put some little holes in it to find the membrane and plastic sheeting which he found.

    Any advice please?

  18. Had 4″ slab poured. Waited a little more than a month, etched and stained it. Now when it’s humid moisture collects on top. It feels oily. What can we do to correct the problem?

  19. Hi Danny,
    Love your show, personnel and all you do to help home owners do work around their home (I’m a retired engineer & project manager in Mobile).
    Anyway, you might want to caution people that when they seal their garage floor, condensate water dripping from our auto A/Cs will not dry as quickly as unsealed concrete, especially in our high humidity and could be slippery. A water aborbent pad could be taped down to help but it’s a little unsightly.
    Thanks again for all y’all do!

  20. Good Morning,
    My floor in my garage retains moisture. It’s got a horrible smell. We can’t handle it. My daughter is continuously sick. It’s not in some areas, but in others. If we put any plastic storage container down, then move it, there’s moisture underneath it. I need help. My husband can’t do any repairs like this anymore, he’s permanently disabled. Who should we call for help and will my insurance cover this? Thanks so much.

  21. We have what looks like spots where condensation come up from around the edge of our garage floor. We do not have moisture/condensation on any parts of the garage floor. I have never seen moisture/water accumulate on the garage floor. The spots come up when we clean them but a few have returned. Please help us with this potential problem.

  22. Install a radon mitigation system it works extremely well and it will remove radon gases along with the moisture that is present. Radon gas will come up underneath the floor whether there is insulation a vapor barrier or some other type of barrier between the earth and the cement floor. A large fan or a small fan depending on the circumstances can be used. Along with the removal of the radon gases you will notice an extreme change in mold the type air Maurice damp type of environment it will change significantly. And it is a very inexpensive way to fix this problem. I am surprised that nobody has proposed a radon mitigation system to remove any contaminants from underneath the cement floor. They work extremely well.

  23. I bought a garage with a cement floor and this month (June) I have a lot of condensation on the floor. Also have cars and parts stored there and am afraid they will rust. There isn’t any paint on the floor and I don’t know if there is any vapor barrier underneath. Any help you can give me would be appreciated. Thank you.

  24. I have a house with concrete garage floor. Recently, there has been water that has come up several time in the middle of the garage.. I would estimate it is around a cup of water. It happens every week or two. The floor has epoxy and sealant on it and the water has not damaged the floor. What should I do?

  25. My new concrete garage was poured over a heavy moisture barrier that I witnessed being used. The moisture that appears on the new floor about a foot from the wall. Is this likely to be condensation that is more common with new concrete? My old garage, which was expanded, is dry. Only the addition floor has the wet problem except where the new concrete floor joins the old one.

  26. I have the same problem as everyone else with the garage but my enclosed patio does the same thing. What do I do?

  27. We have a tiled screen porch on our home. When foggy conditions or high humidity occur, our porch floor gets so wet, it’s a genuine hazard to try to walk across. We’re in Florida and the winters are not really freezing cold, so this can be an ongoing problem for months. Any suggestions? We get tired of bringing out the mop.

    • Hi, Elizabeth!
      There is likely no vapor barrier under the slab the tile is laid on so it “sweats.”
      You may need to install a vapor barrier and new flooring above it.
      Good luck!

  28. Welcome
    If you have cold walls, eg a garage, and the floor is not permeable, because there are tiles or cement coating on it, etc. under the influence of high and low temperatures, condensation takes place and on your floor moisture and puddles of water.
    I have already done more than 100 such services, I applied for this purpose on the wall and ceiling with a thickness of up to 3mm thermal insulation mass which I mentioned in the previous commentary. The British market also has graphene paint that can be used.

  29. Hi, I need your help please for my garage floor.

    I live in Boston and i have a 2 car garage that also 2 floors. It has a garage door and 2 windows on the first floor and 1 window on the second floor. The 2nd floor ceiling also has air vents in the ceiling and the 2nd floor of the garage is insulated and the first floor is made from cinder blocks.

    The structure is probably more than 75 years old.

    My problem is that on some parts of the floor I get moisture (wet spots) and it happens even when it hasnt rained for days.

    In fact, I notice it happens when the humidity is high.

    I’ve been told by folks who have come out to look at it that it’s from water around the garage rising from under the garage and that I need to do the garage floor over and add a vapor barrier. But I cant believe that cause it happens even when it hasnt rained in days.

    Another guy came out here and said I have to seal the floor, and that seems more likely, but I need someone to tell me if sealing the floor really stops moisture in the air from forming on the floor?

    I believe its related to moisture in the air forming on my floor, but need help.

    How can I fix this please?

    I’ve been dealing with it for years.


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