Why & How Do you Seal a Concrete Basement Floor and Which is the Best Floor Sealer to Use
Regardless of what your plans are for your basement, if you have a concrete floor you will want to consider applying a basement floor sealer as a treatment to harden and waterproof your concrete. Deep penetrating silicate sealers are the best way to go, fairly inexpensive and easy to apply they’re a great preventative measure against moisture on your way to a fully finished basement floor.
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We recommend choosing one of the following brands to seal your basement floor…GhostShield, RadonSeal or Foundation Armor… click here to find out why.
Should I seal my basement floor, how do I seal it, how much will it cost and which is the best basement floor sealer to use? These are the common questions we get asked about sealing basement concrete and in this Ask the Pros post we will answer all of them. In this post we are concentrating on penetrating concrete sealers that are absorbed into the concrete, we are not discussing basement floor paints or any other type of topical application that is applied onto the top surface of your concrete floor.
Why You Should Seal your Basement Floor
A concrete floor may look like an impermeable block of cement but the fact is that concrete is very porous. When a concrete floor is poured about half of the water evaporates away as the concrete sets. This water raises upwards through the setting concrete and as it does so it creates tiny channels or capillaries which are left behind in the concrete.
You can’t see these tiny channels but they’re there and if the hydrostatic pressure from outside your home gets high enough then moisture can be drawn up through these capillaries by the lower pressure inside your basement. The result can be a moist and damp basement which at best can lead to a musty unpleasant smelling basement and at worst can lead to mold and property damage. If you have plans to install laminate in a basement, or any other type of flooring for that matter, you will need eliminate the moisture first.
The good news is that a concrete basement floor sealer fills and closes these tiny capillaries and should eliminate these types of moisture issues. When you apply a basement sealer it is absorbed deep into the concrete where its chemical agents then react with the concrete, fusing and filling the tiny channels and essentially waterproofing your concrete and closing off a pathway for future moisture. It also densifies the concrete making it harder and increasing its strength and longevity.
Using a floor sealer in your basement is fairly cheap and easy to do, so we recommend that you cure your concrete slab as a matter of course, regardless of what you plan to do with your basement long term. If you plan to install a floating floor in the basement, like luxury vinyl plank or water-resistant laminate then be sure to read the product instructions for installation. You can be certain they are going to recommend a moisture barrier and often suggest that the basement concrete be cured (sealed) as well.
How to Seal a Concrete Basement Floor
There are three pretty straight forward steps to sealing your basement concrete:
- Clean your concrete thoroughly
- Fix and repair any existing cracks or surface damage
- Apply two to three coats of concrete sealer.
Let’s go through these steps quickly.
Cleaning a Basement Floor in Preparation for Sealing
There’s no need to over think this part. Preparatory cleaning before sealing is different to general concrete cleaning. You can click here for full details on how to clean a concrete basement floor, but here are the basics for an unsealed cement slab prior to sealing:
The point of cleaning your concrete is to remove anything from the surface that could interfere with the absorption of the basement sealer. Also, at this point we’re assuming that your basement floor hasn’t been previously sealed. If it has then that’s a whole different ball game and you will need to remove old sealer before adding new sealer. It’s up to you, but you might want to consider hiring a pro to remove old sealer or floor paint!
Assuming this is the first time your concrete is being sealed then it’s just a case of removing any existing stains, dust or dirt. Dust and dirt will get in the way of the sealer penetrating deep into the concrete and stains will simply get sealed into your floor; although this won’t be a problem if you intend to install a further floor over your concrete. Nevertheless, as with dirt and dust, you’ll want to remove any grease and oil from workshop spills or glue from old flooring (vinyl sheet, etc.) because they will also stop the sealer adhering properly.
For dirt and dust use a hard floor vacuum with plenty of suction. For grease or oil use a commercial floor cleaner that has a degreasing agent in it. For any lumps of glue or mastic you will need some elbow grease and a stiff wire brush or a putty knife (soften with boiling water first), followed by a commercial citric degreaser. When you’ve done all this we also recommend a good mop and rinse with water being sure to let the floor completely dry before going further.
Fixing and Sealing Basement Floor Cracks
Cracks in a concrete slab are pretty common and most are nothing to worry about. They are caused as the concrete floor dries out and settles. For an in-depth look at basement floor cracks, what causes them and what you should do about them, click here. For now, all you need to know is that hairline cracks can be ignored as your sealer will seal these cracks up too.
However, if you have cracks wider than 1/8-inch the these should be fixed and repaired prior to sealing. To repair these small cracks, you also need to seal them but with a different type of product. Use a concrete acrylic sealant or concrete patch repair and make sure you wait the appropriate time for the repair to dry before starting with the basement sealer.
Applying the Floor Sealer
Once your floor is clean, prepped and completely dry (wait at least 2 days after any mopping or power washing) you’re ready to apply the basement floor sealer. Please be sure to read the specific instructions of whichever concrete floor sealer you have purchased. The following instructions are a general guide to give you an idea of what you should expect when sealing a concrete floor, but different products have different instructions.
- Some sealers require you so spray a thin haze of water over the concrete until the floor is damp using a hand pump sprayer. This helps the floor to absorb the sealer but is not required with all products.
- Next you will spray or roll a layer of sealer across the concrete working in sections and overlapping your passes so that there is good coverage right across the floor. Some sealers work better with sprayers than rollers.
- You don’t want the sealer to puddle but you do want a good covering, so if puddling starts just use a roller or mop to spread it thinly over the floor until it is absorbed.
- You may be required to apply two thin layers, one straight after the other, and then let the floor dry or you may need to apply one coat, let it dry (2-3 hours) before adding a second coat.
- You can walk on the floor while the sealant is still wet, but try to work from one end of the room to the other so you don’t miss a patch.
- When applying your second coat paint at right angles to your first coat for better coverage.
- Remember that thin and consistent smooth layers are best, you can always add more layers but you can’t fix layers that are too thick!
Avoid Sealing the Basement Wall Floor Joint
Using a sealer on a basement floor is all about waterproofing the concrete slab that makes up your floor so that moisture doesn’t penetrate through it. It is not a solution in the medium to long term for waterproofing the whole of your basement as a way to exclude leaks.
If you have a lot of rainfall, and high hydrostatic pressure around the outside of your basement it is very hard to keep moisture from finding a way in.
The concrete basement floor is poured in such a way that there is a gap between the basement wall and the floor, this gap is called the cove joint and is where you typically see water seepage when the hydrostatic pressure is high.
It might seem like a bright idea to seal this gap too, but it is not. Sealing the cove joint only forces the hydrostatic pressure to build up somewhere else and over time the water will win out. If you live in an area where the water pressure around your home is a problem then the solution is to install an interior drain tile system that will redirect the pressurized water to a sump pump where it can be removed safely.
What’s the Best Basement Floor Sealer to Use?
So, let’s get down to the nitty gritty and look at your best basement sealer options. There’s really no need to go to a specialist store for this kind of thing. A good quality concrete sealer for your basement can be found at any of the big box stores.
Where you may get confused is in choosing which concrete floor sealer is right for your particular basement situation. The answer to this really boils down to two questions, how new/old is your concrete floor and what are your current moisture levels like? Roughly speaking there are three types of basement concrete sealer:
- A densifying/hardening sealer
- A waterproofing sealer
- A combined densifying and waterproofing sealer.
If you have a new, or fairly recent, basement slab that is already dense (not porous) then a waterproofing sealer will probably suffice. If your concrete basement floor is older and more porous (but is not currently experiencing much moisture problems) then you would use a dual action densifying and waterproofing sealer. If your concrete is old, porous and currently experiencing problems with moisture then you may need to start with a densifying sealer first, wait until that has set before then applying a waterproofing sealer if needed.
It is important that you correctly evaluate your concrete before starting. If you are unsure about the state of your basement concrete or your moisture levels then we recommend consulting a professional before undertaking the work.
It is also important to note that most of these sealers are not sold as a solution for basements with severe pre-existing moisture problems. If you do have severe moisture issues you may need to consider other solutions which include, but are not limited to, installing a proper drainage system, applying an epoxy flooring, or installing dehumidifiers and ventilation.
Once you have decided which kind of sealer you need then you are ready to choose one of the top brands. The three brands you are going to come across most frequently are RadonSeal, Foundation Armor and GhostShield. All three brands have strong reputations, excellent customer service and can be purchased at Home Depot, Lowes, Amazon and other in-person or online retailers.
Wherever you choose to buy your basement sealer, and whichever brand you decide to go with, we highly recommend contacting the manufacturer direct with any questions or concerns you may have before purchase.
We’re confident that you will get good results with any of the three basement floor sealers that we recommend, but if we had to choose our favorite it would be GhostShield due in part to their excellent website that clearly lays out how to choose the right application for your basement.
Right at the top of their homepage is “Find You Product” button that takes you to a questionnaire where you can determine which of their best products is the best for your particular basement. The questions are similar to those we have already discussed, namely…
- Are you taking preventive measures or do you already have moisture problems?
- If you have moisture issues already have you taken a reading of the moisture levels?
- If you’re taking preventative measures are you looking for maximum protection (densifier + water repellent) or are you looking for the most cost efficient option?
Depending on the answers to these questions you can choose between the following products:
Lithi-Tek 9500 – If you have new concrete or concrete in good condition that has never had any moisture issues then Lithi-Tek 9500 is a deep penetrating hardener and water repellent in one and a great cost effective preventative solution. It comes as a concentrate (1 gallon) which you dilute with water to make up to 5 gallons of sealer. Cost is just under $100.
Lithi-Tek 4500 & Siloxa-Tek 8510 – For the fullest protection you can split the job into two sections. Lithi-Tek 4500 is the densifier and hardener while Siloxa-Tek 8510 is the water repellent, both also come in 1 gallon units of concentrate. Lithi-Tek 4500 costs just under $80 and Siloxa-Tek 8510 just under $75. This fuller protection is about 50% more expensive and of course more labor intensive as well. This combination is also what is recommended if you have a small amount of existing moisture in your basement already (under 3lb per 1000 sq/ft).
Vapor-Tek 440 – This last GhostShield product is the only one we’re going to recommend if your basement already has significant moisture issues. It is a two part epoxy coating so it is actually a different type of concrete sealer to the ones we have discussed.
In this instance, rather than penetrating into the floor and changing the density of the concrete, Vapor-Tek 440 works as a moisture barrier that seals any moisture into your concrete. Up to this point we have been considering basement floor sealers that penetrate and densify the tiny air capillaries within your concrete, but these only work on relatively dry concrete floors. If that ship has already sailed and you have more than 3lb per 1000 sq/ft of moisture then sealing the existing moisture into your concrete with a product like Vapor-Tek 440 is the next best step.
Vapor-Tek 440 is also an excellent solution for anyone intending to lay a different flooring type over their concrete slab. If you want to install carpet in your basement or maybe a basement floating floor of cork or vinyl plank flooring and are concerned about future moisture, then applying this protective moisture seal (along with any other plastic vapor barriers or waterproofing precautions) will give you added piece of mind that moisture won’t be creeping up into your flooring from below.
As mentioned Vapor-Tek 440 is a two part coating which you mix together and then apply in one coat leaving a clear gloss finish. It comes in two kit sizes, 1.5 gallons and 3 gallons, and once mixed must be used at once. This is a significantly more expensive solution with the 1.5 gallon kit selling for just under $250 and the 3 gallon at just under $500. We recommend confirming the suitability of this product directly with Ghostshield.
RadonSeal offers two basement floor silicate sealing options, RadonSeal Standard and RadonSeal Plus. You should use Standard on your newer, less porous concrete and Plus on older (more than 20 years old) concrete. RadonSeal doesn’t contain a water repellent, what it does do, as we have been discussing, is close up the capillaries within the concrete and thus hardening the surface and restricting moisture.
Although RadonSeal has Radon in its name it is not the only basement floor sealer to protect against Radon gas. All the densifying sealers we are discussing close up the capillaries within porous concrete that allows both moisture and gases to seep up and through your concrete. It’s also worth mentioning that densifying sealers may help against Radon but it won’t stop gas seepage altogether.
At the time of writing you can purchase 5 gallons of Radon Seal Standard for around $180 and 5 gallons of RadonSeal Plus for around $200.
Foundation Armor also offers two different penetrating densifiers/hardeners, one for dense floors (Armor L3000) and one for more porous concrete (Armor S2000). Once you have applied either of these hardeners you can then follow up with one of their water repellent sealers Armor SX5000 (solvent based) or Armor SX5000WB (Water Based)
2 coats should be all your need to harden and seal your concrete but if you are already experiencing moisture problems you may need extra coats. S2000 and L3000 come in 1 gallon and 5 gallon containers giving you some budget flexibility depending on the square footage of your basement.
Foundation Armor S2000 and L300 can be bought in both sizes on Amazon
- S2000 1 gallon costs around $75
- S2000 5 gallon costs around $225
- L3000 1 gallon costs around $85
- L3000 1 gallon costs around $330
Our Home Flooring Pros wholeheartedly recommend applying some type of basement floor sealer to your concrete as a way to strengthen and protect your floor from future moisture damage or to remediate any existing low level moisture problems.
The types of basement sealers we have discussed are not a magic cure-all for very old and damp basements that were built long before the current building codes were introduced or have been left to deteriorate for decades and are now in terrible shape.
Always get professional feedback from reputable builders before undertaking any kind of basement. renovations.
Q: What should I do if I see efflorescence on my concrete floor
A: Efflorescence appears as a white powdery or crystalline deposit and is a good indicator of moisture within your concrete. It’s not a problem in and of itself, but it’s a sign that using a basement sealer on your concrete floor is a good idea and this salty deposit should be cleaned off the floor prior to sealing.
Q: How much does it cost to seal a basement floor?
A: If you’re doing the work yourself you will only pay the cost of the sealer plus the cost of the roller or sprayer you are using to apply the product.
Q: Can I paint over a sealed basement floor?
A: Yes you can but be aware that any basement floor sealer that contains water repellents will also repel and water based paints.
- Hydrostatic pressure is the pressure created by standing water, so when there has been heavy rainfall or snow melt for example the ground becomes saturated, the water table rises and and the water, which weighs a lot, pushes up against your basement walls creating pressure and looking for a place to go.