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 Josh,
    Yes, I think I would go with a dehumidifer for the interim until you can really figure out for sure where the water is coming in and why. After all, there’s really no point in trying to solve the water problem until you know what the problem is! ;o) Granted, it may take some time to figure out, depending on how long it will be until it leaks again and if you can actually observe where the water is coming in at……..until then it’s a guessing game.
    Good luck and hope you can eventually figure out where the problem lies.

    Reply
  2. part of my basement which is carpeted with industrial grade carpet was soaked when the tubing from the humidifier on the furnace was blocked while we were away in the late spring. Last week I had the carpet taken up when because i thought it smelled. Underneath was so much glue and a black tarry substance neither of which we are able to remove completely. I want to put new carpeting down but should i seal the floor first? I have a dehumidifier and no moisture issues but I don’t know if i should just put a good carpet pad and carpeting down or seal it first.

    Reply
  3. Hi Grace,
    So long as you are positive that you don’t have moisture issues, then you’re ok. BUT, keep in mind that concrete basements do draw moisture thru the concrete from the ground, which is a major reason why carpets become smelly and the basement air feels ‘damp’. Ideally, you should scrape or use solvents to remove the glue and black goo and then seal the concrete, but that’s entirely up to you, it depends on what you can live with yourself. I do think you’ll notice quite a difference if you seal it.
    If you use chemicals to remove the glue & goo, try to find something that has low/no VOC – that’s the fumes that are bad for your health and fumes don’t normally disperse as well in basements because there isn’t usually as many windows/doors to open for the fumes to dissapate.

    Reply
  4. My basement was musty and I removed the carpet many years ago but left the basement floor as is with glue stuck to the cement floor since we had stopped using the basement. Now we are ready to put a floor on it but I still see these very tiny four-legged creatures in the basement.
    They are as big as a grain of salt. I believe they fed on the wallpaper that was also on the gypsum board walls but was also removed a few years ago. Before I go ahead and put new flooring I am worried that once the job is done that these tiny creatures will resurface. We have seen these creatures only in the basement and they are white or off-white in color.
    At the same time I have noticed that some of my books have the same type of creatures but they are brilliant white in color and I looked them up on the internet and I believe they are called book lice which apparently like humid environments and feed on glue or adhesives. With all this said and done, I decided to look into my basement walls and they are covered with fiberglass pink throughout and in addition, a layer of tar only halfway up the height of the
    foundation walls.
    These walls have 60% humidity in them. I was also told that this basement was excavated two feet lower than the normal range of excavation that is done, and it was done to provide a higher ceiling apparently.
    There is also a sump-pump pit that gathers lots of water and works very regularly to remove it. I was advised to remove the existing walls and insulation and that I should put a new soya-based liquid foam that will seal all pores in the concrete foundation walls and will remove about 70% of the humidity in the basement. Supposedly this product is not dangerous for the health and environment and will break the thermal bridge that creates an environment for mould on foundation walls.
    Once I go ahead and do all this, I am still worried that my basement floor will release humidity enough to provide a home for these creatures. So I did a saran wrap test in the last 24 hours and it seems like the floor does not release humidity but I know that in future this can change.
    Keep in mind that during the last two summers I have been running a dehumidifier on my first floor and I empty it out everyday. I do not run it in the basement for fear that if there is humidity or hidden mould that it can be rethrown back into the air once it comes out of the dehumidifier. We are planning to put wood flooring but I am worried that if I put a polyethylene vapor barrier, that over the years water will build up and be trapped between the cement floor and the plastic cover and again provide a home for these creatures to feast.
    My other option is to put a subflor or dri-core floating system directly above the cement floor, however, I am worried that the air gap between the concrete slab and the subflor will allow air to create similar humid conditions if water builds up in this air space enough to provide a home for these creatures to proliferate.However the manufacturer claims that any water build up will flow freely through the raised plastic dimpled pattern towards the basement drain due to the air gap providing air flow. Another option would be to put styrofoam directly onto the concrete floor and then build a wooden floor on top of this but again, I do not know if the concrete slab once and if it releases humidity over time , if these creatures can form and live between the styrofoam and the concrete slab.
    The glue on the cement floor from the carpet that had no underlayment is hard to remove and even if most of it comes out, my worry is that small glue partilces will remain and will provide organic material for these creatures to feed on. So my question is multi-tiered:
    1)if most of the glue does not come out instead of wasting time removing it, being that the urethane application on the walls will remove a good chunk of the humidity, do I still have to seal the cement floor or can I just place the dri-core subflor floating system directly onto the cement floor?
    2)If the glue comes out fully, do I just place the dri-core subflor floating system directly onto the cement slab?
    3)Under either instances (1) or (2), do I have to still put a sealant or tar in order to block humidity from coming out of the cement slab and creating moisture conditions that these creatures will be able to feed on?
    4)Can the sealant or tar, if applied on the whole basement floor, release toxic chemicals over the years that will harm our health?
    5)We are thinking of putting bamboo floors due to their health benefits, do you think they can warp?
    6) Is hardwood bamboo better than engineered bamboo, which do you recommend given the state of our basement?
    7) If none of my ideas are correct to remedy the situation, do you have a better strategy so that we can start using our basement without worrying that we will be seeing these transparent-like tiny creatures all over our basement and stuff?
    The contractor is coming in a few days to start ripping the walls, are you able to provide me with some answers ASAP, it would be deeply appreciated. Thank you for your time and I am glad I found your website because I have spoken to many people and I get many confusing and contradicting pieces of advice?

    Reply
  5. OK, answers to questions………
    1.) I think it would be a good idea to put a vapor barrier on your cement floor – after all, it can only help, right?
    2.) Yes. However, (copied and pasted from DriCore‘s FAQ portion of the site:
    The DRIcore moisture management system allows any seepage or moisture to channel freely under the DRICore subfloor panels to keep floors both warm and dry.
    NOTE: DRIcore is not a replacement for a good foundation nor a solution for home drainage maintenance, flooding, or continued water leakage. Any leaks or excessive moisture should be attended to prior to any flooring installations.
    3.) I would think so, if nothing else than to help cut off the little critter’s food supply.
    4.) Yes & No. If you prefer the “No” answer, be sure to buy a sealer that has Low or No VOC’s. It won’t be a problem to find these brands – most manufacturers are jumping on the environmentally friendly bandwagon. Don’t use tar.
    5.) Any kind of wood flooring can warp – especially in a humid environment. This is part of the reason why you need to acclimate your flooring materials before you ever lay them. So long as the subfloor is even, then ideally your flooring should be too.
    (again, copied & pasted from their website) DRIcore panels may be required to acclimatize for longer periods depending on the humidity and temperature of the room where the installation is to take place. The recommended humidity and temperature to be maintained for a below grade installation is 30-50% relative humidity and 21° C (70°F).
    Allow panels to stand for at least 48 hours by stacking or laying them out on the floor with the plastic cleated surface down. During seasonal periods of high humidity conditions such as June, July or August, it is recommended to acclimatize DRIcore panels simultaneously with the finished wood flooring to be installed for about 2 weeks to allow for the balancing of the moisture contents of both products. Check with the finished flooring manufacturer for their recommended temperature and humidity guidelines.
    6.) I would think that engineered bamboo would be a better choice, mainly because it would most likely expand & contract better with the humidity and temperature changes.
    Sounds like you’re on the right track with your thinking, need to address the critters if possible. I’ve read that fresh air & sunlight helps to control their numbers aside from chemicals of course.
    Good luck with your project!

    Reply
  6. We are in the process of purchasing a house. The basement of the house has a mixture of 9×9 tile and painted floor. The house was built in 1959 and the basement tile is from that period. We found a white fluffy pouder like deposit coming from under the paint and also from under the tiles.
    What is this? Is it harmfull? How would you remove it, and/or prevent it from reocurring? Is this a deal breaker?
    Any comments would be appreciated.

    Reply
  7. Hello in Wisconsin!
    I’d insist that samples be taken of this powder and that it be tested for asbestos. It’s probably efflorescence, but it would be smart to be sure. This could indeed be a very real and scary problem considering the dust. If it is asbestos, then it has obviously deteriorated so badly that really, only a professional should remove and dispose of it. Yes, it’s costly, but remember, it can be deadly.
    I don’t know how you’re planning on financing this home, but if it would be a mortgage, many times the seller will have to pay to have it fixed because the bank will insist on it as part of the deal. Obviously, if it’s asbestos, then the Realtor and seller would still have to disclose this even if you decide not to buy this home. Face it, they’ll have a tough time selling it as-is if this is asbestos.
    I’m not quite up the federal laws, but I wouldn’t be surprised if it were even illegal. Businesses, schools, etc. have been shut down when asbestos is found and cannot reopen until it’s been cleaned up and inspected and given the green light to reopen. Asbestos particles become airborne and float everywhere, which is what makes it so hazardous to your health. I seriously doubt the seller would be allowed to sell it if somebody blew the whistle about the asbestos.
    Again, that’s if it’s asbestos, which I’d be almost willing to bet it is. Get it checked out ASAP.

    Reply
  8. Thank you for your post. I am assuming your concern about asbestos will be because of the tiles? I did some research and I think the pouder substance is “efflorescence” and it is caused by moisture from the basement floor. Assuming that the asbestos issue is resolved, is there a way of preventing the moisture from penetrating the basement again? will a sump pump work, sealing the basement floor?? We will talk with our agent today and see what are our next steps. Thank you.

    Reply
  9. Hello again,
    Just for the sake of health concerns, I sure hope you’re right and it’s ‘just’ efflorescence. I’m sure you know that efflorescence is caused from moisture seeping up through the basement floor. The only way to keep it from happening is to address the moisture problem itself. I’m presuming the floor is concrete, right? Problem is that efflorescence damages the concrete (and it’s integrity). Hopefully, it’s not damaged to the point where you’d need to jackhammer the concrete and and pour a new basement – which is a very extreme scenario.
    Does the basement flood? Just wondering since you were inquiring as to whether a sump pump would help. If it floods, then yes, a sump pump would help to remove the water faster, but it still doesn’t address the moisture itself. You may need to have a professional come in and see if they can figure it out and advise you what to do.
    Do you have any idea where the moisture is coming from? I know that can be a really tough question considering you don’t live in the house.
    There are quite a few different ways to address moisture issues, but it’s going to depend on the source(s) of the moisture. There’s dri-core systems, vapor barrier paint, plastic sheeting, fixing cracks in the floor, etc………
    Sometimes, problems can be addressed by simply having a few feet of gravel around the house (which can be landscaped to look nicer) can take care of water coming in the basement, but it just depends.
    Do you plan on having an inspector check out the house? That’s usually a requirement for obtaining a loan and if you have a good inspector, often times they’ll have a good idea of what a moisture problem stems from.
    Wish I could be of more help, but without knowing the source of the moisture, it’s next to impossible to tell you how to remedy the problem.

    Reply
  10. Hello again, I appreciate your answers from August 10 concerning my basement and I was thinking of trying a different strategy. I would like to apply a product called Demilec Airmetic Soya that is a urethane supposedly all-natural onto the basement floor and completely cover the glue stuck to the basememt floor slab. Once the urethane is applied then I would let it dry and then apply 2 inches of sandcoat (sand and cement)directly over the urethane. Then I would install ceramic tile on top. 1) Do you think that this procedure would alleviate any humidity from forming on the basement floor tile? 2) Do you think that the tile will keep warm with or without heating the basement?
    As for the basement walls they currently have tar on them from the basement floor up to the level of the land outside, then they have fiberglass pink , and then they have a paper barrier that has an aluminum coated siding and then there is the drywall. Now I had the walls tested with a humidity meter reading and they seem to have anywhere from 60-90% humidity in some places. I opened the wall in two areas and when I removed the fiberglass pink it was dry, and the wall is not wet at all. Under these conditions what shall I do: 1) Should I leave it as is and just buy a dehumidifier and run it everyday to remove the excess humidity? or 2) Shall I rip open the walls and start from scratch and apply urethane on all the perimeter walls and omit the need to run a dehumidifier all the time? Do you have any recommendation other than my two options? Keep in mind that the book lice like to feed on glue, wallpaper and thrive in hot humid conditions. Thank you for answering before and I hope you do not mind answering me again on this new strategy.

    Reply
  11. Your flooring suggestion sounds ok so long as the urethane is recommended for use as a vapor/moisture barrier. I think your floor will be cool to the touch without in-floor heat, it is underground, and it’s just always going to be cool.
    I’m hesitant to advise you further on your walls, this is a flooring site afterall. In other words, my knowledge doesn’t extend to walls. As far as the humidity in the drywall, remember, you’re going to be blocking a lot of that humidity when you do your floor. It might be worth it to do the floor, use a humidifier for a few days or so and test the walls again. It very well could be that the humidity in the walls is residual from the humidity in the air via the cement floor. It sounds like the walls were taken care of so that moisture couldn’t seep through them.

    Reply
  12. Hello again, I appreciate your answer from August 21, with respect to the basement I found a glue remover that will supposedly remove all the glue from the basement floor, It is called the Glue Buster from Surf-Pro products. Once this is done, my cement slab shall be cleaned with methyl hydrate and then it should be okay and free from glue residue that those little critters feed on. However,1) before I install the Dri-core, shall I seal the cement slab with a sealer, an epoxy water-based paint, an epoxy glue or shall I leave it bare.2)By sealing it, do I trap the humidity in the cement slab which can create potential cement deterioration in the future. 3)Does the slab have to breathe.4) If you do recommend sealing it, which product is the least toxic and does not off-gas, the sealer, the epoxy paint, the epoxy glue. 5)there are a few little cracks in the cement, shall I just use a cement contact to seal them or shall I use a sealer. 6)My main concern is the health of my family and I do not want anything that I put to be toxic and release fumes after many years into our home, what do you recommend!

    Reply
  13. Hello again! So glad you found some products to remove the food source of those little fiends!
    You can use any of the products you mentioned for sealing the cement, just make sure that the product you use will seal fine cracks along with the cement. Most manufacturers are very concious of consumer’s wants & needs and have responded by developing products that are low or no VOC (volitale organic compounds – the fumes & off-gassing that you’re worried about). Manufacturer’s are getting ‘greener’ all the time! You shouldn’t have a problem finding a product to meet your needs, there are lots of them. ;o) If you go to Lowe’s, Home Depot, or something similar, just tell them that you need a moisture or vapor sealer for a basement floor that has a few fine cracks and that you want something that’s low or no VOC, they’ll fix you right up.
    It’s very possible that this will take care of your moisture issues you won’t even need the DriLoc flooring system. I don’t know if you saw it, but I have an article on DriLoc here.

    Reply
  14. We have a 2 year old ranch with un unfinished basement. We are getting so much dust in the house, upstairs and down. I was wondering if we sealed the basement floor if that would help. I am thinking about having the duct work cleaned out too (I think the contractors swept stuff into the floor vents when the ..ahem….cleaned up)I also have 2 good size cracks running across the basement floor. What should I use to take care of those?
    Thanks for your help.

    Reply
  15. Hi Rick,
    I don’t think that sealing the basement floor is going to help with the dust issue. I really think you’re hitting the nail on the head with the idea of having the ducts cleaned out.
    There are products that can be found at your local hardware store to fill in the cracks in the basement floor. What kind of warranty did your new home have from the builder? You certainly shouldn’t have cracks across the basement floor after so short a time.

    Reply
  16. I have a water problem in my basement. I have a french drain and have a sump pump in the basement but water still gets into my basement. I have tried Dry Loc water sealant but water still comes into the basement. What I want to do is coat the entire cement floor and quarter way up the cement walls with roofing tar. When the tar is set I will then cover the floor with ceramic tiles. Will this keep out the water?? Is it worth a try or am I creating more problems??? thanks-

    Reply
  17. Hi Brian, I wouldn’t use roofing tar, it releases harmful vapors into the air that you certainly wouldn’t want in your home. You need to determine where the moisture is coming from first before you can figure out what actions to take to remedy the problem. There are brush-on products that can be used to seal the floor and walls but I cannot tell you whether it’d be recommended without knowing more about where the water is getting in at. I would suggest that you click on the “Moisture Proofing” link on the right hand side – there you can read more about different options that you may have for a remedy to your problem if you know it’s source.

    Reply
  18. Thanks for your response. I’ve tried two different types of brush on products and neither one worked. The water (1 inch sometimes more) comes in after heavy rains so its a matter of hyrdostatic pressure. The water comes up through the cement floor (there are no cracks) and also at the seam where the cement wall and floor meet. The house is only 5 years old. I had one contractor guarantee a water proofing system where he would install a drainage pipe in a trench INSIDE the perimeiter of the basement – for ten thousand dollars!
    I am looking for a more reasonable solution. Hope you can suggest a solution. thanks

    Reply
  19. Hi Brian,
    There’s so many thoughts passing through my brain about your situation and the thought that keeps coming back is that the real
    issue needs to be resolved — keep the water from coming in, or
    at least confine it to one space.
    My old basement had a sump pit with a sump pump. That kept the
    water confined so the rest of the basement was dry and only
    the pit was wet. The pump took care of it.
    It’s also possible that your French drain needs to be repaired or improved. Is the daylight opening
    below the drain? Is it plugged? Did the foundation get water
    sealed properly? Lots of questions here – and that’s outside the “The Flooring Lady” realm as it’s more to do with construction type issues rather than flooring.
    Some type of a stay dry floor-system would be fine, IMHO, if your floors only got
    damp rather than wet. Mold is a concern and still would be even if your floors only got damp.
    Yeah, you really, really need to figure out something to keep the floors from getting wet in the first place, and this does indeed usually require a pretty big expense for something as major of a problem as you seem to have.

    Reply
  20. we have a 98 year old house that has a cement basement. it was made from river sediment, we are told, and the cement has small as well as pebble-sized particles. my question is, do we need to do something special to seal this type of concrete or will a good sealant fill in the many bumps and divets caused by the inclusion of larger rocks?
    thanks,
    kathy

    Reply

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