Sealing Basement Floors

Basement floors can be a problem to live with and to finish if you have moisture problems. There are several ways of dealing with the moisture, including filling cracked basement floors, sealing the basement floors, using a dehumidifier and/or sump pump, and laying moisture barriers for basement floors — prior to installing your flooring choice.


Sealing basement floors is very important. Although most people may think that it is unnecessary because there is carpet or other flooring covering it, sealing your concrete or cement basement floors can prevent mold and mildew from developing and can help your flooring to last longer. Basement floors are especially susceptible to moisture because they are underground and the concrete is directly touching the dirt. Unsealed concrete will act like a sponge and wick water into the basement, and this can cause various problems in your home, including mold, mildew.


A large percentage of homes may have a water problem in their basement and the inhabitants may not even realize it! Mold, algae, and mildew growth can cause health problems for all the members of your family and can even cause death if a person is exposed to it for a long period of time. This is why it is of utmost importance to seal your basement floors to make sure that this will not be a factor in your home.

How does water enter your basement? There are a few different ways. Cracked basement floors are one of the ways that water can get into your basement. Water can be moved into your basement through your concrete floors if they are not sealed. Humidity could also cause a moisture problem in your basement. The first thing to do is to make sure that as much water as possible is moved away from your home via French drains, gutters, grading, filling cracks, and drains. Dehumidifiers and sump pumps can be invaluable in some areas to further keep moisture at bay. Then you will be ready to learn how to seal basement floors and walls to keep your basement moisture, mildew, mold, and algae free.

Seal your basement floors and walls to keep water from the ground soaking into the concrete. There are many different options for sealing basement floors. Read the instructions on the sealant that you choose to make sure that you know how to seal your basement floor and to ensure that it will work just as it is designed to. Applying the sealant as directed will help your floors to be dry and mold, mildew, and algae free for years.

Sealing your basement floors will also help your flooring to last a long time. This way you will be able to put down any flooring that you choose without having to worry about it being damaged by moisture or water. There are also moisture barriers for basement floors that are available for use in addition to sealing the basement floors. Using both methods will allow you to have peace of mind in putting down your new flooring.

If you are having moisture problems in your basement, you will want to take up the existing flooring to try to determine where the moisture is coming into your basement. If you have more than hairline cracks, then you will want to mix up some mortar to fill the cracks. Make sure that all cracks are filled before you seal the floor. If there are not any cracks, then moisture may be coming from the ground underneath your flooring. Applying a sealant will definitely help if this is the case.

Sealing basement floors is a way to take care of your health by preventing mold, mildew, and algae and will help your flooring that you lay down over your concrete to last much longer. Keep the moisture and water away from your basement by sealing your concrete basement floors to help your health and your flooring budget!

77 thoughts on “Sealing Basement Floors”

  1. Hi Kathy,
    I doubt a typical sealer will fill in the “many bumps and divets”, but you shouldn’t have any problems sealing it. You might want to consider a clear epoxy coating though, which will do a better job of filling in, or even a thin layer of concrete and then sealing that.

  2. Hi Kathy,
    We will be listing our house for sale next month. We have an unfinished basement and are talking currently to a company to reseal an old crack in a wall, which has leaked some water. Our realtor suggests that we seal the basement floors and walls, so it looks clean and assures the new owners. Will sealing take care of possible mold as well? Without adding a lot of expense, what type of products/services would you recommend?

  3. Hi Sue,
    So long as the floors and walls are sealed well to prevent moisture, then yes, it should take care of the possibility of mold growing as well. Sealing floors has been covered many, many times on this site, I recommend that you look at the links on the right-hand side of the page and click on “moisture proofing” to see what kind of method(s) would suit your situation best.

  4. Hi – I am going to finish my basment. It has a concrete slab floor in good shape. A few times a year after a really, really hard rain, there is one small spot in and near a corner that appears damp, goes away after a couple of hours. Doesn’t happen anywhere else. No standing water. No cracks. I am going to carpet the floor. What should I put down prior to carpeting in terms of sealant or vapor barrier?
    Also, the walls are cinder block and were painted white about 40 years ago. They don’t get moist or damp so should I leave them as is or paint over them with Drylock paint? Thanks for your help.

  5. Hi Barry,
    Look on the far right of this page and click on the link for “Moisture Proofing” – you’ll find lots of info there to read up on. As far as your walls, if they don’t get damp then I don’t think it’s going to matter if you use drylock paint or not – it would fall under the category of “what do you want?”.

  6. Hi There,
    I’ve got a 170 year old house and have two issues in the basement. The first is the simple fact the concrete floor was poured about 40 years ago by the man who rennovated the house. They are not level and when wet have pooled areas. Even bigger (because I’m working on sealing the basement better) is the fact the ceiling is low (about 6 feet). Is it possible to grind down a concrete floor and gain a few inches, or it that completely nuts? The other issue I have is actually overhead. I’ve got wire and insulation (which are dusty and seem to grow cobwebs) and I’m looking for some kind of fabric with vapor barrier qualities to staple up there and cover it all up. Have you got any suggestions for these two oddball issues?
    Thanks you much, Ken

  7. Hi Ken,
    This is a flooring site, so I don’t feel that I can help with the ceiling issue, though I’d think just some sort of breathable plastic barrier would work.
    While the idea if grinding down the cement floor might sound crazy, it’d be worth a shot if that’s what YOU want to try to do. You might still need to put a thin skin of concrete on it afterwards, but should help give you a little head space.

  8. Hi Brain,
    We had the same problem you are experiencing in your basement. Water was seeping through the floor and where the wall meets the floor. They suggested that we have new drain tiles installed in the basement for $10.000. We decided not go this route.
    We called the Rotor Roeter. They cleaned out our drain tiles and their equipment was able to clean out some small tree roots as well. This was last Spring and have had a perfect dry basement and the sump pump runs all the time again. Don’t wait to long since your basement walls may begin to bow due to the high water pressure. We now are also running clean water through the drain tiles which helps to keep clay and silt to a minimum. It is in particular important that you do this step during the summer months since clay becomes hard and acts as a stopper. Hope this info helps.

  9. what is the best sealant to use for an existing moisture problem in concrete flooring (15 lbs of moisture) – we have a vinyl floor product called Konetco from Canada and it is bubbling in some area due to the moisture in concrete release the glue

  10. Hi Bobbi,
    At this point, there isn’t much you can do until you’re ready for new flooring. The flooring would have to be removed and then the moisture problems dealt with. There’s more on the site about different methods/products for dealing with moisture proofing.


  12. Hi Sheri,
    Go to the top of the page and all the way to the right – click on the link for “Full Archives” – you’ll find info there that can help you. There are also epoxy paints – that way you can do this in one step. ;~)

  13. Had warer come in on existing painted basement floor, paint has bubbled in places and a fine dust or mold is growing, have tried cleaning with bleach but some mold returned, what can I do? Will I have to scrape all paint off and re seal? Home is 40 years old but we use our basement a lot.

  14. Hi Barby,
    Hopefully you won’t have to resort to that, but you really do need to address *how* the water got into the basement. I’m guessing that you probably do need to strip the paint and reseal. Read right above your post too.

  15. Hi Amber,
    I can’t really say that there is a *best* sealer for basement floors because it depends on what method you choose to seal with as well as what kind of a moisture problem you have. Check out the Moisture Proofing section to find out what sort of options are available.

  16. We have water sipping through the sub-floor tile in our storage closet. We have had a plumber replace the storm drain line in the basement, we have detached the down spout and it drains into the yard. After attempting to solve the problem there is still water in our basement. We believe that the water is due to water sipping through concrete that is not level with our drive, which causes the water to stand at low points and sip back into the house. What do you suggest?

  17. Hi Roz, The first thing you need to do is to get a foundation specialist in to try and determine where the moisture is getting in. You might need to have a sump pump installed below the concrete floor and the foundation specialist would know about.

  18. Hi there, I live in a 2 year old semi-detached home. My carpet in the basement that came with the new home has been wet (damp) since we moved in. I was told by the builder when i complained that this was normal for a new home. I tried pursuing it and put a gadget that tracks humidity in the room. Although the air was somewhere between 55 and 76% humidity the carpet is always very damp. Is it possible that there is a problem with my foundation or that my builder did not put down a vapour barrier? I haven’t lifted up the carpet yet to see what’s under it. I do believe, however, that mold has set in. It has a musty smell.

  19. Hi Tara, Damp carpet in a new home is NOT normal. It is entirely possible that your contractor did not put down a moisture barrier. If one was not installed, then I would see what recourse you have with the contractor.

    Otherwise, it sounds like the carpet will be need to be removed and you might consider having a foundation expert come in and assess if there are any foundation problems.


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