Why You Should Use an Epoxy Primer for Your Floor Coating

epoxy floor primer
Epoxy floor primer

When to use an epoxy floor primer is a subject that is often overlooked by the average home owner who is investing in a premium garage floor coating.  In fact, many people aren’t aware that they exist or think that it’s just an added cost by the manufacturer that they don’t need.

Epoxy primers provide an abundance of benefits for your coating with some specializing in problems associated with the surface of the concrete itself. With exception to the inexpensive one-coat epoxy paint kits, if you want to insure that you achieve the best possible adhesion and endurance of your garage flooring for years to come, then you should seriously consider the use of an epoxy primer for your floor.

Benefits of an epoxy floor primer

The benefits of using an epoxy floor primer for your garage are many.  Let’s take a quick look at these to get a better understanding of what they do.

  • Epoxy primers are thin and provide for better adhesion because they penetrate into the concrete substrate for a better bond.
  • Primers provide for a better chemical bond of the thicker epoxy base coat which results in a longer lasting and more durable garage floor coating.
  • Because of their thinner nature, epoxy primers help to eliminate bubbles and pinholes that can form due to outgassing of the concrete.
  • They allow for the subsequent base coat to achieve a higher dry film thickness and coating uniformity since it is not soaking into the concrete.
  • Some epoxy primers are effective in providing a moisture barrier for garage floors that have light moisture problems such as efflorescence.
  • Most are moisture tolerant and work well when being applied in high humidity areas of the country or concrete that has not fully dried from being cleaned or acid etched.
  • Some are specialized such as oil blocking primers.  These are solvent based primers made to cover concrete that has been contaminated by oil and can’t be completely cleaned.

How epoxy primers work

Epoxy adheres to concrete by forming a mechanical bond within the pores of the surface.  This is why you need to profile the surface by either etching or grinding the concrete.

Primers are designed to penetrate deeper into the pores in order to achieve a better mechanical bond to reduce the chances of delamination of a properly prepared surface.  As a result, it also produces a thinner epoxy film or tie coat that the next coat can chemically fuse with.  This process produces an even stronger bond yet and is why most contractors always use a primer.

air bubbles and pinholes in epoxy floor coatingAir bubbles, craters, and pinholes can be created in epoxy from outgassing of the concrete.  Air in the slab will rise due to a temperature increase or change in humidity.  If it does this during the initial application and curing process of a 100% solids epoxy without primer, it can form these bubbles, craters, or pinholes when the air escapes the concrete.  It can also happen due to poor mixing of the epoxy or improper back rolling.

Because of their thinner film, primers reduce the likelihood of bubbles and pinholes forming as they soak farther down into the concrete to fill those voids that can hold air and reduce the chances of air finding its way to the surface.  If air does find it’s way to the surface, the bubble will usually pop and then slowly fill back in before curing due to the low viscosity of the epoxy primer.

Since most epoxy primers are water based, the chemical makeup provides for moisture tolerance and as a result some brands can actually be applied to a damp slab.  This is beneficial for the DIY epoxy installation that profiles the slab with acid etching.  Instead of waiting 24 -48 hours or more for the slab to dry completely, you can apply your primer when the concrete is still damp or if the humidity is up.

Many of these same primers will also form a vapor barrier to ward off the problems associated with moisture that tries to work its way to the surface.  If you think you have a moisture problem, contact the manufacturer first to determine how much moisture you can have in order to use their product.

Oil stop epoxy primers

Finally there is epoxy primer for those who thought they could not epoxy coat their garage because of oil contamination that could not be removed completely.  Some manufacturers make an oil stop primer that is solvent based and works by actively seeking out and bonding to the oil contaminants embedded in the concrete.

These are usually dark in color however and need to be covered with more than one base color coat or with a full refusal paint chip application.  If not, the darker color may bleed through and alter the color coat.

Will your epoxy floor coating fail without a primer?  No, if you prepped your floor correctly, chances are your coating will not fail.  However, with all the benefits that can be gained from using an epoxy floor primer, it’s hard to come up with an excuse not to. They are definitely something to strongly consider and most cost less than the standard epoxy formulas due to their thinner film thickness.

If you want the most durable and trouble free coating that you can have for your garage, then the investment for an epoxy primer is going to be worth it for years to come.


    • Shea says

      Hello Grant. If you have a very good profile that was achieved by grinding, then most polyaspartics do not require a primer. However, always check with the manufacturer. Some applications may require thinning of the first coat and this acts as a primer.

    • Shea says

      Hello Miguel. Epoxies do not “require” a primer to work. However, a primer is a wise choice to use for all the reasons mentioned above and is also why professional installers use primer. They can’t afford to put down a coating that they might need to come back and repair at a later date, so they insure the quality of their coating by using it. You can install most epoxies without a primer and have good results if you have prepped the floor properly, but you will not benefit from the additional gains that a primer will provide.

  1. Jeromy says

    For a basement, should I use water based or 100% solid epoxy? Should I use a primer? If so what kind? I’ve decided on Armorpoxy, Armorgarage, or Budget Bob’s as my 3 possible companies I will order from. I would like this floor to be my permanent floor. Any suggestions? I’ve just heard that Rustoleum Epoxyshield (even the Professional kit) is not very good durability.

    • Shea says

      Hello Jeromy and thanks for visiting our site. Your question depends on how durable you want your floor to be. If you are looking for a high build coating that will give you the best protection for the dollar, then 100% solids epoxy is the way to go. Many manufacturer’s will use a water based primer however since it is not being used as the build coat. Both ArmorPoxy (which goes by ArmorClad for their residential products) and Armor Garage sell and recommend using a primer. Budget Bob’s does as well. ArmorPoxy and Armor Garage provide very good products. Budget Bob’s product changed after his death a few years ago. They do not provide technical data sheets online to compare, so we don’t have an opinion about their product.

      For long term wear, the EpoxyShield kits are not your best bet. The Professional series is better, but it is solvent based and you don’t want to be applying that in an enclosed area of the home. Also if you haven’t done so already, make sure to do a moisture test first since it will be applied in a basement.

  2. Nick says

    Hi I had a couple of questions. I have spoken with three different professional installers, all touting what they apply as best which is making it difficult. However when discussing application, none of them mentioned a primer. All stated basically grind (or shop blast?)\clean, apply color coat , chips, top coat. When asked what about a primer coat the basic response was oh, the product mfg has that all figured out in the product itself.

    That sound odd to you? I want the longest lasting floor possible and I’d think they would not want warranty issues so why would they all skip the primer step? (BTW my garage floor 1 approx 1k sqft and about 10 yrs old w typicla dirt\stains if it matters).


    • Shea says

      Nick, you’ve been asking about both polyaspartic/polyurea coatings (PAP) and epoxy coating in different articles on our site. It’s not unusual for professional installers of PAP systems to not use a primer. PAP coatings are typically thinner than commercial epoxy, the base coat can be made less viscous for better penetration, and due to the fast cure rate, vapor transmission doesn’t have much of a chance to form bubbles.

      For epoxy some installers will thin the first coat of commercial epoxy which will act as the primer. Others may state what you cited about the manufacturer stating that it’s all figured into the formula. That, in our honest opinion, is just good marketing tactics by the manufacturer in order to try and make their product look better. It is not a substitute for primer though. As we stated in the article, no epoxy manufacturer states that you have to use a primer. However, many good installers use them for the reasons stated above. If you feel confident in the work of the installer, if they were willing to offer references, and they have a good warranty and are known for standing behind their work then I wouldn’t worry too much.

  3. Nico says

    With the 1 coat epoxy systems, can I apply a primer to make the system more durable or does it do more harm than good?

    • Shea says

      Hi Nico, applying an epoxy primer first will always improve the performance of a quality epoxy product. It allows for a thicker dry film thickness of the base coat since it won’t be absorbed by the concrete and better adhesion as well. Technically you would have a 2 coat system this way.

  4. jared says

    Hi, I am wondering if I can use epoxy /epoxy primer on a freshly poured garage floor or would this not allow the concrete to cure properly. Essentially what I’m looking for is a glossy looking floor that I can spill oil on and just wipe it off, also what could I put on it to make slip resistant?


    • Shea says

      Hi Jared. You need to wait a minimum of 28 days, preferably longer if you can, before applying epoxy or most any topical film forming sealer to a freshly poured garage floor. Moisture is being released during the curing phase and will interfere with the adhesion process. After that you will need to acid etch or grind it in order to apply the epoxy. One coat of primer by itself is not recommended. Primers are designed to penetrate the concrete and can leave a blotchy look. If you apply a second coat of epoxy or polyurethane over the primer, then you will get the glossy look. Polyurethane is the best for adding an anti-slip additive like Shark Grip. It will make the floor slip resistant.

  5. Greg Trelfa says

    i coated my shop floor 15 yrs. ago with Rustoleum Professional Floor Epoxy. It has lasted very well but it’s time to be repainted. What steps should I take to ensure a quality job?

    • Shea says

      It all depends on the shape of the current epoxy Greg. If it is only worn in a few places, looks dull, but adhered well and not peeling up, you can always recoat it. We talk about that here. If it’s too worn out you will need to grind the floorto remove the existing coating in preparation for new epoxy. We have many articles with tips on applying epoxy, plus a DIY epoxy installation guide. You can find them here.

  6. Roy Foreman says

    I have a clean but dimpled concrete garage floor. I do not like the thought of grinding or using acid. Can I produce a sound finish by simply coating the rough concrete with a couple of coats of good primer prior to adding the paint surface. The garage houses one car and is lightly used. Thanks

    • Shea says

      Hi Roy. Assuming you are wanting to apply a 2-part resinous coating such as epoxy and not just paint, you are required to acid etch or grind the concrete first or it will not bond to the concrete correctly. A primer is not a substitute for proper concrete prep. It has the same requirements of the concrete before application. If you want to review a product that does not require acid etching or grinding of the concrete, we recommend that take a look at Rust Bullet concrete coating. However, you still will have the issues of the dimples.

  7. Leisa says

    I love your forums!! For a DIY person, they are extremely informative and very helpful!

    I purchased Armor Garage’s Armor Chip Garage 100% solids epoxy flooring. I didn’t buy their primer because they told me that it was not necessary. I have read a lot of online forums and get mixed responses about this, for the reasons that you have outlined above. While acid etching my garage floor, I could see very tiny bubbles coming up through some of the cracks. While I am planning to fill all of the cracks that I can see with SIka Crack Filler (followed by sanding), I am worried that there might be some micro-cracks that I missed and which may be a source of rising air bubbles. I am thinking that a primer would help address this concern. It will take me a week to order & receive their primer and I am wondering if I can just go to the local Sherwin Williams commercial store near me and use one of their Armor Seal Epoxy Primers so that I can apply it tomorrow. They have a 100% solids epoxy primer/sealer as well as two different water-based epoxy primers, and can be found here:

    1. In reading all of your extremely helpful and well-written forums, am I correct in assuming that I could use one of these as a primer or will there be some type of compatibility issue with Armor Garage’s epoxy base coat? I don’t understand why there would be compatibility issues but the SW customer service guy said you could only use products within the same line. I am assuming they are saying this more for liability reasons rather than technical reasons but am not sure. Is that assumption correct?

    2. If I can use the SW primer, can I go with the water-based epoxy primer or does it have to be 100% solids to match the 100% solids base coat?

    3. And if I can go with water-based epoxy primer, which I am thinking I can based upon what I have read on your website, is one of these 2 products better for me to use: ArmorSeal® Floor-Plex™ 7100 Water Based Epoxy Primer vs. ArmorSeal® Water Based Epoxy Primer, and if so why? Just trying to learn here. :-)

    It’s a Saturday and I would like to try and buy this today so that I can apply tomorrow. I’m not sure if you’re checking this forum, but any insight/help that you can offer me would be greatly appreciated!! Thank you in advance.

    • Shea says

      Hi Leisa and thanks for the kudos. There should not be a compatibility issue with using a different vendor’s epoxy primer, especially water based. That said, it could effect how Armor Garage would react if there is a problem with your coating. We know that Armor Garage sells very high quality product. Unfortunately however, they are one of the few vendors who do not make their TDS sheets readily available. As a result, we can’t determine which SW primer most closely resembles what Armor Garage offers.

      If you want to put down an SW primer anyhow, you do not need the high build 100% solids. The Armor Garage base color coat is already a high build coat. You would be better off with the higher solids water based primer.

      Do not worry about your micro cracks. The primer coat will take care of those if you choose to use it as will the Armor Garage high build color coat by itself. The key is to apply the first coat after the temps have peaked and started to cool. This significantly reduces any chances of water vapor wanting to rise up through the slab into the epoxy. The bubbles you saw coming up while etching is perfectly normal. Just make sure your floor is bone dry before applying the epoxy.

      Also, make sure your crack filler is sandable. Many have made the mistake of purchasing SikaFlex self-leveling crack sealer which is not. It’s also not paintable.

        • Shea says

          We can’t recommend a primer that you can buy locally. With few exceptions, most all quality garage floor coating products need to be ordered. If you are going to order then it would be best to go with what Armor Garage has. The epoxy crack product that you linked to will work just fine.

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