Rust-Oleum EpoxyShield and RockSolid are arguably the most well-known DIY garage floor kits. As a result, we get more questions from our readers regarding their application and subsequent problems than any other coatings available. And one of the more common questions is, what kind of concrete primer can be used for EpoxyShield, RockSolid, and similar DIY garage floor coatings?
The answer may surprise you. EpoxyShield and RockSolid do not require nor recommend the use of a primer. This includes any other brand of low-solids or water-based epoxy coatings. But why you ask?
The reason is fairly simple. However, this is an area where more people make the unfortunate mistake of applying what they think is the correct primer to use. So, let’s discuss what not to use and why. In addition, we will reveal when a primer should be used and for what type of garage floor coatings.
Lastly, with this newly acquired information, we will discuss why a primer should not be used for EpoxyShield, RockSolid, or similar store-bought DIY garage floor coatings.
Concrete Bonding Primers Should Never Be Used for Garage Floor Coatings
When it comes to primers for epoxy and other floor coatings, the biggest mistake made is to use a concrete bonding primer. Examples are Behr Concrete & Masonry Bonding Primer, Seal-Krete Lockdown Primer, Kilz Concrete Bonding Primer, etc.
These are all very thin film, single-component latex, and acrylic concrete primers that are not compatible with coatings. Epoxy, Polycuramine, and similar coatings will not adhere well, if at all when applied directly to concrete bonding primers.
To adhere, it would require roughing up the surface of the bonding primer with 150-grit sandpaper after it has dried. This allows the coating to form a mechanical bond with it.
Bonding primers are primarily used when applying paint and 1-part epoxy paint. If you do not understand the difference between concrete paint and concrete coatings, then it’s crucial to learn about the differences here.
Most importantly, concrete bonding primers do not form the same tenacious bond to properly prepared bare concrete as a true epoxy or similar concrete coating. As a result, the bonding primer becomes a severe weak link in the coating system.
What Kind of Primer is used for Garage Floor Coatings?
The correct primer to use for concrete and garage floor coatings is epoxy primers. And we don’t mean a “concrete primer” that is applied before epoxy. When you hear the term epoxy primer mentioned, it means an actual 2-part epoxy coating that is specifically formulated for use as a primer coat.
These are typically commercial-quality water-based epoxy coatings that are designed to wet out for good penetration and create a high bond strength to concrete. There are even 100% solids epoxy primers (no water or solvents) with special bonding characteristics. These high solids primers are not intended as a wear coat.
Here are examples of epoxy primers from our sponsor Legacy Industrial.
Like all coatings, 2-part epoxy primers chemically cure after application. When a base color epoxy coat is applied to the primer coat within the recoat window, the two coatings form an unbreakable chemical bond with each other.
Many epoxy primers are clear. However, some vendors and manufacturers offer colored epoxy primers that match the colored, high-solids base coat. This is particularly advantageous when applying a white coating or very light grey and tans over dark concrete. It helps to prevent ghosting of the concrete color through the lighter colors.
When Should Epoxy Primers Be Used?
Though it’s not a requirement, epoxy primers are highly recommended to be applied to properly prepared bare concrete before applying a high-solids (>80%) to 100% solids epoxy.
One of the primary reasons for this is that high solids epoxy is very thick. It can be upwards of 3 – 6X thicker than store-bought DIY coatings, depending on the solids content and coverage rate used. As a result, they don’t wet out and penetrate the concrete as well as an epoxy primer.
When an epoxy primer is applied, the high solids epoxy will obtain a chemical bond to the primer coat. This is a stronger bond than what it would obtain to the bare concrete.
The time to get high solids epoxy applied is typically 30 – 40 minutes depending on the current air temperature. This is known as the pot life. As a result of this short time, any air transfer or outgassing from the slab can get caught in the thicker epoxy as it cures. This can result in trapped air bubbles or pin holes. Applying an epoxy primer first prevents this from happening.
You can read in more detail why an epoxy primer should be used here.
Why EpoxyShield, RockSolid, and Similar Thin Mil Garage Coatings Don’t Use Primers
Now we know what type of primer should be used for coatings. So, let’s discuss the simple reason why they are not recommended for RockSolid, EpoxyShield, and similar coatings.
It all has to do with cost, value, and performance. Water-based DIY epoxy kits are thin mil, budget coatings. One gallon of epoxy primer typically costs more than a single-car EpoxyShield Kit (one gallon). In addition, an epoxy primer will perform better. So why spend more on an epoxy primer only to apply an inferior (EpoxyShield) epoxy color coat over it?
Read: Rust-Oleum EpoxyShield VS RockSolid Garage Floor Coatings
RockSolid Polycuramine penetrates and bonds to properly prepared concrete similar to an epoxy primer. However, Rust-Oleum states that RockSolid polycuramine should not be applied to epoxy unless it has fully cured.
This requires deglossing and roughing up the epoxy with sandpaper before applying RockSolid. This requires additional time and labor, not counting the additional cost of the epoxy primer.
In both cases, you are better off applying two color coats of EpoxyShield or RockSolid instead. The first acts as the primer coat. It’s cheaper to do this with EpoxyShield and it saves time and labor for RockSolid.
RockSolid has its own problems in terms of value though when you do this. Two coats of RockSolid are more expensive and no thicker than a single coat of a much higher performing, commercial-quality single-part polyurea coating. So why do this if you can apply a much better coating for less money?
What About Rust-Oleum Concrete and Garage Recoat Primer?
Many people confuse Rust-Oleum Concrete and Garage Recoat Primer for epoxy primer. It’s not.
This particular product was designed by Rust-Oleum to be applied over previously sealed bare concrete or older coatings that are adhered well. No prep is required other than cleaning first.
It is not to be applied to unsealed bare concrete or worn-out coatings that are peeling or have numerous bare spots. It’s the lazy man’s answer to avoiding proper prep work and can only be used in conjunction with other Rust-Oleum products.
We reviewed this product and discuss how works and when it should be used in this article here.
Final Thoughts
The store-bought DIY epoxy garage floor kits are intended for single coat applications to bare concrete. They are a popular budget solution to your garage floor coating needs.
If you believe you may require more than one coat to achieve the proper thickness and/or color before you begin your project, then you really should be looking for a better coating.
There are far better DIY garage floor coatings and coating systems that perform much better than what you can find at your local home improvement center or hardware store. If you would like to learn more about these, we suggest starting with our epoxy and garage floor coatings information section.
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