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Urethane vs. Epoxy Primer – When to Use Which

In many industrial and commercial settings, the best way to protect a concrete floor is with a well-specified and professionally installed resinous coating system, which should always start out with an appropriate primer coat. Urethane (also referred to as polyurethane) and epoxy are two resin types frequently utilized in the manufacture of primers. Your flooring contractor is likely to recommend a flooring system that includes either an epoxy or urethane based primer. Knowing more about these two types of products can help inform your discussions.

FloroPoxy MVT Epoxy Primer used as the first coat in this colorful high performance floor by Florock UK of Great Britain.

FloroPoxy MVT Epoxy Primer used as the first coat in this colorful high performance floor by Florock UK of Great Britain.

Choosing an epoxy or urethane based primer will depend as much on the overall flooring system selected as on the type of facility, the room environment and the daily activities taking place in the space where the coatings are to be installed.

Unique Characteristics of Urethane Primers

When today’s resinous flooring professionals talk about “urethane primers”, they are usually referring to cementitious urethane primers. Also called urethane mortars, these products are very different from what one may think of as thin film polyurethane clear coats and high performance urethane topcoats. Cementitious urethane primer, slurry and troweled materials are unique in that they contain a Portland cement component. As the first coat in a multi-layered, 3/16”-1/4” thick urethane mortar flooring system, cementitious urethane primers provide excellent surface penetration and bond to mechanically prepared concrete substrates.

Unlike many epoxy base coats, cementitious urethane primers are moisture tolerant and can be applied to concrete floors that are consistently damp, such as in food processing plants, or even over “green” concrete. Because the standard minimum cure time for a newly poured slab is twenty-eight days prior to application of most other floor coatings, construction managers greatly appreciate the time saving option of polyurethane mortar systems that allow installation of the cementitious urethane primer as early as five days after fresh concrete placement.


Thanks to their Portland cement content, like urethane mortar systems as a whole, these primers expand and contract at a rate very similar to concrete. When exposed to drastic swings in temperature, cementitious urethane primers can maintain their good bond.

Despite these many outstanding benefits, urethane mortar primers and their compatible cementitious flooring systems are not right for every application. Mixing and application techniques can be quite technical, with many manufacturers requiring contractors to undergo special training and certification prior to installing. In fact, the great majority of floor coating systems actually start out with epoxy primers.

Epoxy Flooring Primers

With the exception of urethane mortar flooring systems with their cementitious urethane primers, most industrial, commercial and institutional floor coatings get installed over epoxy primers. As a rule, epoxy primers bond tenaciously to correctly prepared concrete and provide an excellent base for subsequent coats, whether a creatively decorative, high traffic flooring system or a heavy duty 1/4” thick epoxy-aggregate mortar floor. Low viscosity epoxy primers help fill the pores of the concrete and can begin the job of evening out small imperfections in the slab surface. They are an economical, tried-and-true solution on which many experienced flooring professionals rely.

Standard epoxy primers require a dry substrate and do not perform well over damp concrete. However, new moisture tolerant epoxy primers are available and offer a good option for certain environments. Current technology enables industrial grade epoxy primers to be manufactured completely solvent free, with zero V.O.C.’s. Many have lower odor installation and offer accelerated cure times to ensure faster turnaround.

Knowing What is Right for You

Both cementitious urethane and epoxy primers offer superior benefits under certain conditions. Your regional floor coating representative and local factory-approved installer can help design the best system, including the optimal primer, for your facility’s application. Whatever your unique flooring needs, at Florock, we’re ready to help.