As corrosion challenges intensify across key industries, coating technologies are under greater scrutiny. While thermoset powders remain the standard, thermoplastic coatings are gaining ground for their durability, repairability and resistance to harsh environments, making it essential for coaters to understand how each system impacts performance, cost and service life.

Contributed by Michael Withers

Although thermoset powder coatings have long been the industry standard due to their balance of performance and process familiarity, thermoplastic powder coatings are emerging as a compelling alternative, particularly in demanding service environments. Their inherent toughness, ability to be remelted and repaired and strong resistance to chemicals, moisture and impact make them well suited for applications where long-term durability is critical. For coaters and specifiers, understanding the fundamental differences between thermoset and thermoplastic systems is essential to making informed decisions that align performance requirements with cost, maintenance expectations and service life.

Thermoplastic powder coatings are the preferred coating due to their superior corrosion and chemical resistance. Therefore, this specialty coating is found in household appliances such as dishwashers as well as pesticide sprayers on farming equipment.

Thermoset vs. Thermoplastic Powder Coatings

Thermoset powder coatings, commonly based on polyester, urethane or epoxy chemistries, undergo a crosslinking reaction during curing that permanently sets the coating. Once cured, they do not reflow when reheated, which makes removal difficult and typically requires sanding, blasting or chemical stripping. Field repairs are generally performed using liquid coatings and application is most often done via electrostatic spray.

Thermoplastic powder coatings (TPPC[SL1] ), including Polyvinyl Chloride (PVC), polyolefins (polyethylene or polypropylene), and nylon (typically PA-11 or PA-12) chemistries, do not crosslink. Instead, they melt and flow over the substrate, encapsulating it. This enables them to reflow when heated, making field repairs much easier. They can be applied using electrostatic spray, hot flock spray or fluidized bed dipping, offering flexibility in application methods.

As far as film build and applied costs are concerned, there are differences when comparing thermoset and thermoplastic powder coatings. First, thermoset coatings are typically applied at a film thickness of 2 to 3 mils, with an applied cost ranging from approximately 5 to 10 cents per square foot.

Thermoplastic coatings are generally applied at much higher film builds, typically 8 to 12 mils, and can go even higher when required. Their applied cost is usually in the range of 30 to 40 cents [MW2] per square foot.

Benefits of Thermoplastic Powder Coatings

The key differentiator is corrosion performance. When applied above 6 mils, thermoplastic coatings exhibit no microporosity, whereas thermoset coatings inherently contain microporosity at their recommended film builds. This makes thermoplastics far superior in aggressive, corrosive environments.

Thermoplastic coatings are generally not decorative, and color options are more limited. However, in applications where corrosion resistance is critical and color is still important, a hybrid system can be used: thermoplastic as a primer with a thermoset topcoat. When proper application guidelines are followed, this approach is successful and enables access to a full spectral range of colors and even metallic finishes.

That said, primer/topcoat systems represent only a small percentage of thermoplastic usage. Most thermoplastic applications are direct-to-metal, single-coat systems.

Playsets are commonly coated with thermoplastics not only because they are safe for children to touch, but because their soft feel is pleasing compared to thermoset coating’s feel, which offers a colder, harder touch. In coastal locations that require regular maintenance and recoating with liquid or replacing the part entirely, TPP offers superior corrosion performance.

Substrate Concerns and Common Applications for TPPC

Let’s address some of the issues related to corrosion performance. While the coating does assist, it does not stand alone. It is a part of system: substrate, pretreatment and powder coating.

Before we get into coatings or applications, let’s talk about substrates. Steel has the least corrosion performance and needs the most help from the rest of the system. Proper pretreatment is critical to long term performance.

Galvanized steel [MW3] has better performance but still needs the proper treatment. Even galvanized steel will corrode, especially if it is pickled to remove oxides then left unprotected to the environment. Once pickled, it is highly reactive with the moisture in the air and will rebuild oxide very quickly. The problem then becomes at the powder coater, your pretreatment system isn’t built to remove heavy deposits of zinc oxide. Therefore, you can experience early coating failure in the field.

Cast iron has many difficulties to overcome. First, you have to deal with outgassing. Tiny bubbles come out of the cast material and create pinholes in the coating. Second, are the impurities that can lead to early corrosion failures.

Cast aluminum has different issues. The choice of aluminum alloy is generally made for its strength and flow performance in the mold. Often corrosion performance is sacrificed or ignored. A380 alloy is often chosen for its flow/strength properties but due to its impurity content, it has one of the least corrosion resistant performances. A356 and A360 have much better corrosion resistant performance but don’t match A380 in other areas.

Extruded aluminum has very good performance with proper pretreatment. The alloy choice is often based on other properties and corrosion performance is consistent across the choices.

Stainless steel has its own challenges. Due to impurities in the steel, you can see very different corrosion performance across the many alloys.

Bus stops and other city signs that are made of aluminum are exposed to harsh ice melting salts and chemicals during winter months. Thermoplastic powder coatings provide protection from these strong chemicals and salts.

Now let’s look at applications.

Chain link fencing: Colored chain link fencing found in sports complexes, music venues, city parks and residential or commercial properties is typically coated with polyvinyl chloride (PVC) thermoplastic powder coatings.

Dishwasher racks: One of the most well-known applications is dishwasher wire racking. These components must withstand thousands of cycles in slightly alkaline environments with elevated water temperatures. Weld joints and cut wire ends are especially vulnerable to corrosion. Nylon thermoplastic coatings have become the industry standard for this application because they consistently perform.

Playgrounds and recreational structures: The softer feel of polyethylene (PE) thermoplastic coatings makes them ideal for playground equipment. Their corrosion resistance also makes them suitable for coastal installations where thermoset coatings often struggle due to lower film builds and microporosity.

Design trends increasingly include welded grid floors, stair systems and railings. Thermoplastic coatings excel in these applications, offering durability, textured slip resistance and ease of field repair.

Marine and coastal environments: In marine or brackish environments, PE or HDPE (high density polyethylene) thermoplastic coatings provide exceptional protection. Applications include boat anchors, railings, tie-downs, lighting structures, birdhouses, and both residential and high-rise coastal railings. These are among the most corrosive public-use environments, and thermoplastics consistently perform well.

Agricultural equipment: Polyethylene thermoplastic powder coatings also provide superior chemical resistance. Fertilizer and pesticide sprayers are exposed to aggressive chemical environments where thermoset coatings can struggle.

Wind energy structures: Wind turbines are expected to operate for 25 years or more, often in coastal or offshore conditions. PE thermoplastic powder coatings offer the durability required to meet these environmental challenges.

Urban infrastructure: Bus shelters, light poles, signage and transit enclosures are routinely exposed to deicing salts and other corrosive chemicals. While aluminum substrates help, they are not sufficient on their own. Thermoplastic coatings significantly extend service life in these environments.

Pedestrian bridges and city parks: Pedestrian bridges, whether steel, galvanized, or aluminum are expected to last decades. Thermoplastic coatings provide corrosion protection that meets these expectations and can be field repaired without removing large structures, dramatically reducing life-cycle costs.

Anti-graffiti applications: Concrete underpasses and retaining walls are prone to graffiti. Thermoplastic coatings naturally resist adhesion and can be cleaned more easily than many thermoset systems, making them a compelling solution.

Pools and water facilities: Swimming pool fencing, railings and filtration components are exposed to chlorine or saltwater; both highly corrosive. Thermoplastic coatings protect these structures especially well, including cast aluminum components where alloy selection can present corrosion challenges.

Cost Considerations and Process Efficiency

For job coaters, selecting the right coating system is often a balance between substrate limitations, corrosion performance and throughput. The overall system cost for a new system requires and understand of your largest part size and what primarily is j80you’re your business. Perhaps very large parts shouldn’t be on the conveyorized line but coated with a batch system. Thermoplastic powder coatings can be [SL4] applied through the same guns but adjust to the settings is often needed.

An epoxy primer with a polyester topcoat can achieve corrosion protection, but it requires two coating and cure cycles, increasing time and cost. A thermoplastic system, while more expensive per pound, can often achieve equal or better corrosion resistance in a single-coat process.

When comparing total applied cost, throughput and operational efficiency, thermoplastic powder coatings are often competitive and sometimes more economical than multi-coat thermoset systems.

Both salt water and chlorinated pools are aggressive in causing premature corrosion, but with fencing around pools that are coated in thermoplastic powder coatings, long-term corrosion protection is guaranteed.

The Higher Price of Thermoplastic

The difference in cost between thermoplastic and thermoset powder coatings begins with manufacturing. Thermoset powders are formulated, blended, extruded, cooled into brittle chips and then ground into powder using an air-classifying mill[MW5] .

Thermoplastic powders, due to their lower melt temperatures, require a different approach. After extrusion into pellets, they are ground using an air-classifying mill with the addition of liquid nitrogen. Liquid nitrogen prevents melting during grinding but significantly increases production costs; one of the primary reasons thermoplastic powders are more expensive.

Thermoplastic powder coatings are not a universal replacement for thermoset powder coatings, but in corrosive, high-durability environments, they offer unmatched performance. The best recommendation is always to consult with a coatings specialist to determine the most effective solution for your specific application.

Metal fencing can enhance the appearance of a home, but if using thermoset powder coatings, routine maintenance is necessary. Thermoplastic powder coatings have better corrosion performance and significantly less organic growth potential, so maintenance is significantly reduced.

Michael Withers is business development manager, architectural powder coating and thermoplastics, North America, at Axalta Coating Systems.