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 or vendor 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.


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.


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. This reduces any chances of delamination of a properly prepared surface. The primer also produces a thinner epoxy film or tie coat that the much thicker base coat can chemically fuse with. This process produces a much stronger bond of the base coat and is why most contractors always use a primer.

Air 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 this happens during the initial application and curing process of a high solids or 100% solids epoxy to bare concrete, it can form these bubbles, craters, or pinholes when the air escapes the concrete.

As a side note, these bubbles can also happen due to poor mixing of the epoxy or improper back rolling.

Because of their thinner film, epoxy primers reduce the likelihood of bubbles and pinholes forming. They do this as they soak farther down into the concrete to fill the 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 as well. 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.


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 high solids epoxy formulas due to their thinner film thickness.

If you are going to spend the money for a commercial quality, high solids garage floor coating, then it’s well worth the few dollars more for an epoxy primer. It will help to provide the most durable and trouble free coating that you can have for your garage and the investment will provide a great return for years to come.

You get what you pay for!      4/16/18

So, what are they getting? Both the Rust-Oleum Epoxyshield and Quikrete epoxy paint is an actual 2-part water based epoxy coating — one part is a tinted epoxide resin and the second part is a polyamine hardener. Both have approximately a 50% solids content by volume with the remaining being water. Commercial  or higher quality epoxy have 100% solids,  a huge difference.  The water acts as a carrier agent for the epoxy and allows it to be applied very easily, just like paint and that is why they are marketed as such. SO WHY THE PROBLEMS WITH RUST-OLEUM AND QUIKRETE?

The other scenario is the online shopper looking for a deal on epoxy floor coating products. They find great deals online for these epoxy garage floor paint kits with all the promises of a beautiful epoxy floor for less than half the price of other epoxy systems. They then make the purchase not really knowing what they are getting.

What happens, however, is this water base evaporates as the epoxy cures and what you are left with is just over 50% of what originally went on the concrete. Actual dry film thickness is approximately 3 mils for the Rust-Oleum Epoxyshield product and 2.4 mils for Quikrete.

Best yet would be a higher quality epoxy that has up to 100% solids with no VOC’s to worry about. It’s more difficult to work with and you have a shorter period in which to do it, but when it cures, very little evaporates and what you have left is 100% of the product on your floor. As an example, epoxy paint is on average 2.5 mils thick when cured and 100% solids epoxy is 9 to 12 mils thick.

So as you can see, there is a big difference between a one coat product such as the Rust-Oleum or Quikrete epoxy and the much thicker and more expensive multi-coat system of commercial epoxy floors. You cannot expect to get the same protection, durability, and shine from these simple one coat kits that you do from a higher quality commercial product.

The big issue though is that many home owners are not aware of these differences in epoxy floors and expect the best from the lesser expensive kits.

Another problem is poor preparation of the floor when these kits are installed. This is probably the biggest mistake that is made. The pores of the concrete surface need to be exposed in order for epoxy to mechanically bond to it. This is called profiling the concrete. Rust-Oleum and Quikrete both give you a citrus acid cleaning solution to use on the concrete to help expose these pores, but the problem is that it’s not always effective. Many times you need something stronger such as muriatic acid to etch the floor   or even better, concrete grinding.

A few drops of water on various spots of the floor can test this. If the concrete turns dark and immediately absorbs the water, then the concrete is profiled correctly. If it sits there without absorbing right away, the pores are not exposed and the epoxy will not bond well.

Poor profiling of the concrete is what causes the delamination or peeling of the epoxy paint within a few weeks or months. The pores of the concrete must be exposed and be free of all oils and dust. It takes more work to prep the floor than it does to apply the epoxy paint. Poor floor preparation is the cause of most bad coatings.