In 1907 Leo Baekeland, a Belgian-American chemist, developed a new synthetic polymer with a combination of phenol and formaldehyde that he called Bakelite.  Since then additional synthetic resins were developed that formed a basis for protective and decorative polymeric coatings.

In 1936 Pierre Castan synthesized a Bisphenol A type epoxy by reacting epichlorohydrin and in 1946 the first epoxy adhesive was commercialized.  This was followed in 1937 when Otto Bayer invented the polyurethane resin.  Finally, in 1988 polyureas were developed.

Over the years, epoxies, polyurethanes, and polyureas formed the backbone technologies for high performance coatings.  Among these polymers, polyureas exhibited outstanding commercial acceptance compared with epoxies and urethanes, where an amine is made to react with a polyisocyanate to produce a fast-setting coating.  Polyureas have advantages as a coating system that includes rapid cure (usually less than a few seconds), high elongation (>400%), excellent abrasion resistance (<10 mg loss Taber Abrasion), and outstanding tear strength (>50N/mm).  However, the fast cure of polyureas requires specialized and relatively expensive plural-component spray equipment for application.

Polyfunctional amine compounds such as polyureas are used as co-reactants for polyisocyanates in many applications, but the use of these materials over time was limited by their very high reactivity and short gel time.  The little or no pot life did not allow widespread use of these resin systems in many coatings applications.

Before the turn of the twenty-first century, new environmental regulations pushed suppliers of raw materials to develop resin systems that meet new low VOC requirements without sacrificing performance.  The development of polyaspartic resins in the 1990’s was the result of this effort.

Polyaspartic esters, a specific type of polyurea resin, were developed to provide high performance and allow formulations with low VOC, together with relatively moderate reactivity.  This extension in the rate of cure, compared with rapid-cure conventional polyureas, allowed the use of polyaspartics in coatings formulations that offer an acceptable pot-life and working time for application.  In addition to a more practical gel time, polyaspartics provide:

  • One-coat application – normally applied at 6-8 mils, but can be applied up to 16-18 mils, or more, in a single coat application;
  • Rapid curing compared with epoxies and urethanes — resulting in a return-to-service in a few hours or the next day;
  • Weatherability – UV stable, color-fastness and non-yellowing compared with epoxies, along with high gloss and stain resistance;
  • Tough, Hard, Abrasion-Resistant Films – Scratch, abrasion and scruff resistance is greater than epoxies or urethanes;
  • Low VOC’s – Can be formulated for low viscosity at high solids or without solvents and with excellent flow and leveling in contrast to solvent-dependent epoxy and urethane coatings formulations where solvent odors restrict use;
  • Low-Temperature Applications – Can be applied at temperatures from -30°F up to 140°F;
  • Chemical Resistance and Good Mechanical Properties — Enables a wide variety of applications; and
  • Flexibility – Polyaspartics can now be formulated with extraordinary flexibility and strength, allowing for application on flexible substrates such as wood, plastics, and metal.

These characteristics make polyaspartic coatings ideal for concrete flooring applications as well as many other applications, including:

  • Concrete Resurfacing
  • Direct-to-Metal
  • Wood Coatings
  • Plastics Coatings
  • Wind Turbines
  • Hybrid Technologies
  • Composites
  • Gel Coats
  • Patching Compounds, Crack Fillers and Putties

The Chemistry of Polyaspartic Coatings

Aspartics are prepared by a Michael Addition reaction of di-amines onto maleic acid di -esters which are secondary aliphatic di-amines. Steric hindrance is built into the molecule via the di-amine, which has a significant advantage over conventional polyamines, the use of which is limited by its extremely high reactivity with low-cost aromatic polyisocyanates. Thus, polyaspartics make up a special class of hindered secondary amines whose reactivity can be custom-designed for desired performance using conventional application methods.

Compared to the typical secondary amines, polyaspartic chemistry allows coatings to be formulated with sufficient pot life as well as low viscosity to allow the use of a brush or roller.  In addition, faster return-to-service has enabled polyaspartic coatings to save time and money for the applicator.

Compared to the traditional polyurethane chemistry, the reactivity between the amine and the aliphatic polyisocyanate in polyaspartic chemistry enables the formulator to forgo using a tin catalyst, and this allows the polyaspartic coating to be applied at higher film thicknesses than the traditional polyurethane coatings. This minimizes bubble formation and bubble release caused by the carbon dioxide gas produced by tin when it catalyzes the isocyanate reaction with water.  Bubbles and foam are especially present when polyurethane coatings catalyzed with tin are applied at higher levels of humidity.

The Technology of Polyaspartic Coatings

The technology of polyaspartics for coatings was developed in the early 1990’s and initial project work focused on reducing VOC’s in automotive base-coats.  For this purpose, polyaspartic amines were used as reactive modifiers of polyols or as reactive diluents to replace solvents in polyurethane coatings systems.

Towards the close of the 20th century, paint contractors took note that polyaspartics could be applied onto concrete in one-coat, whereas the conventional system at the time required 1-3 coats of epoxy and often followed by 1-2 coats of polyurethane.  This system allowed a 2-car garage to be completed in one day rather than several days as required by a combination of epoxy and urethane.  The contractor charged the same amount to the customer for the one-day job, compared with 2-3 days’ work for alternate systems, and the paint crew went to the next job the day after.  Polyaspartics enabled the contractor to be much more efficient – in fact, some contractors learned how to finish two garages in one day with the quick return-to-service of polyaspartics.

Going into the 21st century, the commercial growth of polyaspartics in the hands of paint contractors was relatively slow.  Some contractors heard about the efficiency of polyaspartics by word of mouth, but polyaspartic coatings at the time were formulated with limited pot life or working time in the range of 10-20 minutes.  Coatings manufacturers recommended the use of solvents to extend the working time from 10-12 minutes or from 14-16 minutes, depending on the formulation, to working times that were double or even longer.  Solvents in polyaspartic formulations extended working time and reduced viscosity of the system, and use of solvents also lowered the cost of the system.  But these same solvents also introduced objectionable odors and safety hazards to both workers and clients.

In 2016 a new technology for polyaspartics was introduced to the industry by Pflaumer Brothers, Inc., consisting of new, low viscosity trimer polyisocyanates developed specially to extend the working time of 2-K polyaspartics.   Continuous research by Pflaumer focused on innovative chemistries to develop a new polyaspartic amine, commercialized in 2018, used by itself or as a modifier to extend working time in combination with conventional trimer polyisocyanates.

Pflaumer also introduced new functional additives during this period to improve flow and leveling along with bubble release, thus improving overall appearance with brush and roller applications.  Reactive and non-reactive diluents were added in 2018, replacing conventional solvents and enabling the formulation of high solids polyaspartics at low viscosities. Colorants specifically developed for polyaspartics by Pflaumer were introduced that enabled the formulator to offer special designs both indoors and outdoors to their clients.

Thus, by 2020, the coatings chemist was able to formulate polyaspartics with working time, color, appearance, performance, and application properties approaching that of epoxies and urethanes – but with a system capable of one-coat application and a quick return-to-service.

Properties of Polyaspartics

Polyaspartic polyurea overcomes many of the practical complexities of a polyurea, while retaining the finest properties of both polyurea and aliphatic urethane. Polyaspartic is a type of polyurea (actually a polyaspartic aliphatic polyurea) where the –NCO terminated pre-polymer is reacted with secondary or hindered aliphatic di amines, resulting in polyurea linkages, but giving ample time (20-30 minutes) for application by conventional methods like brushing or rolling.

Polyaspartics have a relatively low viscosity compared with conventional polyureas, and they provide good wetting ability onto properly prepared concrete and can be applied at higher dry-film thickness in a single coat, apart from UV stability and excellent chemical and abrasion resistance. Polyaspartics can be applied at a wide range of temperatures, bonds easily to concrete surfaces, and cures to touch within an hour. It can be formulated to be flexible enough to bridge small cracks, and can withstand relatively higher temperatures when cured, and impart bubble-free, high gloss films.

The stunning advantage of polyaspartic chemistry is its fast cure which means that there is virtually no down time and one thick layer can be applied in a single application in a single day. The coating is easily applied at room temperature, requires no external heat source for curing, and the surface can be walked on after just a few hours.

Applications of Polyaspartics

Polyaspartic coatings deliver innovative solutions for coatings on steel for corrosion protection and are recommended along with a zinc-rich primer for long-term durability and protection. Compared to two or three or more coats required for epoxy protective coatings in the past.  Now the coating scheme consists of a zinc-rich primer and a one-coat polyaspartic topcoat, ensuring excellent corrosion protection while maintaining the requisite film thickness. For the last 15 years, polyaspartic coatings have proved their usefulness as protective coatings in protecting wind turbines, bridges, industrial plants, food processing plants including breweries and wineries, and agricultural and construction machines against corrosion.

Though the polyaspartics were developed about 20 years ago for coating steel to prevent corrosion, their high performance features led to use as concrete floor coatings. Many companies promoted polyaspartics for floor coatings for industrial and commercial uses and polyaspartics thus entered the floor coatings market. Polyaspartics are known throughout the coating industry for outstanding one-coat performance and fast return-to-service.

The entire focus of the floor coating industry today is to provide customers and contractors user-friendly dependable coating systems that can be installed with consistency and speed. Concrete floors are notorious for cracks and joints which present a unique problem to rigid epoxy floor systems when continued movement either from thermal or load transfer factors cause reflective cracking in the epoxy polymer floor coating systems.

These cracks are then subject to increased wear from mechanical traffic and serve as a collection point for liquids, dirt and debris leading to undercutting and progressive damage to the flooring system. Recoat windows are another concern when applying multiple coats, as epoxies need 8-24 hours for curing of every layer.

Today, the facility owners do not have sufficient time to allot to the flooring contractors because of the fear of the delayed return to service, which ends up in production losses and so are wary of the conventional flooring coatings systems that take a minimum 3 days to return the coated floors back into service.   And as if by design, polyaspartics meet these expectations for return-to-service.

Epoxies have been the industry’s workforce floorings for a long time, because they are relatively inexpensive, easy to apply and deliver good results — at least at first. Epoxies will start cracking at floor joints, bulge at vulnerable points, fade in direct sunlight, yellow with age and are prone to hot tire pick-up. In short, epoxies are better in aesthetics, but are poor in properties due to their very low elongation (<3%) and, in addition, epoxies take a long time to cure and to complete the job within a reasonable period of time.

Urethanes are fast curing and have all the desirable properties needed, but are very sensitive to moisture and hence have limiting factors. Polyurea, due to its rapid curing, tends to follow the contours of the surface to which it is applied without leveling or filling in depressions or ridges, thus giving a textured look. Polyaspartics overcome all the above deficiencies and look aesthetically much like a typical self-levelling epoxy.

Polyaspartics have almost three times the abrasion resistance of epoxies, and are more flexible and UV stable. When comparing polyaspartics to urethanes, polyaspartics have the advantage in high film build properties as they are not as sensitive to moisture as urethanes and are far less likely to bubble. Polyaspartic coatings can replace the two layer system of an epoxy base coat and urethane top coat with one coat system which is faster to apply and provide superior performance properties.

Overall, the chemistry of polyaspartics provides comparable performance and appearance to that of both epoxies and urethanes but with one-coat application.  In addition to one-coat application, polyaspartics coatings offer fast return-to-service with commensurate savings for labor, down-time, and other resources on total project costs – altogether a savings of 20% to 60% of the total cost of a project compared with multi-coat applications required for epoxies and urethanes.

The cost savings for a one-coat application of polyaspartic is compared with a multi-coat application of epoxy and urethane on a steel bridge in a case history.  A portion of the bridge, consisting of 12,264 square feet was coated with a 3-coat system consisting of one coat of a zinc-rich primer, one coat of an epoxy base coat, and one coat of a urethane top-coat.  Another portion of the same bridge consisting of 10,525 square feet was coated with a zinc-rich primer followed by one coat of polyaspartic.  The rate of application of the 3-coat system was 383 square feet per day, and the rate of application of the 2-coat system was 502 square feet per day, a difference of 31% in productivity.  The cost to paint the 3-coat system was $102/square feet, while the cost to paint the 2-coat system was $77/square feet.  The two-coat system was applied in substantially less time than the 3-coat system, allowing the bridge to return to service much more quickly.

This cost savings is being recognized throughout the world where time to complete a job and the cost of labor are important.  And this is why polyaspartic coatings are gradually becoming a strategic choice compared with epoxies and urethanes in the global marketplace for industrial and maintenance coatings.