Surface finishing is essential for the practical use of reactive metals like ductile iron and carbon steel. When left unprotected, the iron in these metals reacts with oxygen to form rust. This means that colorful exteriors aren’t just decorative—they are functional barriers that prevent corrosion.
Metal parts can be finished with either powder coating or wet paint. While they serve a similar function, each coating type has a unique set of advantages and disadvantages.
Both coatings contain resins, additives, and pigments. The major distinction is solvent: wet paint contains solvent, but powder coating doesn’t.
The solvent in wet paint keeps all the other components in suspended liquid form. In contrast, powder coating is applied as a dry powder. All the other differences between powder coating and wet paint—application method, color matching, texture, and even operator training requirements—stem from that basic difference in chemical composition.
Despite being applied in different states (liquid versus solid), the industrial application methods for powder coating and liquid paint are surprisingly similar.
Pretreatment is identical in both processes. Before any coating can be applied, the surface needs a thorough cleaning. Any oil, dirt, moisture, or other contamination will interfere with surface adhesion.
After cleaning, the processes diverge slightly.
For the powder coating process, dry powder is shot through an electrostatic gun on to the metal exterior. The gun gives the powder a negative charge, and the negatively charged powder is attracted to the grounded part. The attraction results in fast, even application.
Once the coating reaches the desired thickness, the coated piece is placed in a curing oven, where the heated powder gels. Curing creates thermal bonds between powder particles, resulting in a smooth, hard finish.
Liquid paint is dispensed in a fine spray. It is also electrostatically charged, but to much less effect. While powder coating forms even coats with almost effortless ease, liquid paint needs to be applied by highly trained experts to avoid drips or sags.
Some liquid paints are air dried, while others are placed in a curing oven.
It is normal for both powder coating and liquid paint to include a primer and a color coat, however, liquid paint may also include multiple color coats and a clear top coat.
In some applications, the appearance of the finished paint job is nearly as important as performance.
Some textures can be attained equally well by powder coating or wet paint, but others are easier to achieve with a particular medium.
Textured finishes are much easier to attain with powder coats. Thinner powder coats are naturally more textured, while thicker layers are smoother.
It is technically possible to attain a high-gloss finish with powder coating, but it is much easier with liquid paint.
Powder coating has many strengths, but liquid paint is the unequivocal winner when it comes to color matching.
Custom colors of liquid paint can be mixed on-site, and with a high degree of precision, by almost any paint supplier. A blue and red pigment can be mixed to produce purple paint.
In contrast, custom powder coat colors require a special production run. The color of powder coatings is determined by the plastics ground down to form it. There is no solvent in powder coating, so an attempt to blend blue and red powder will just create a blue and red speckle pattern.
Because it is hard to color match, powder coating is usually produced in large batches of standard colors. Custom orders are possible, but more time consuming and expensive than color matching with wet paint.
A finish is meant to protect metal surfaces from corrosion and other environmental damage. If the finish is damaged by scratching or chipping, it ceases to function as an effective barrier.
Powder coating provides better performance than wet paint—it is more resistant to chipping, scratching, and other wear because of the thermal bonding it undergoes during curing, and because it can be applied in much thicker layers.
In addition to its physical toughness, powder coating provides superior color retention. Long term exposure to moisture, sunlight, and heat breaks down the resins found in both paint and powder coating. This process, known as chalking, causes resin and pigment particles to lose adhesion. Affected particles form a chalk-like layer on the coating surface.
The early stages of chalking merely give the coating a faded appearance, but severe chalking will eventually erode the coating enough to compromise surface protection. The rate of chalking depends on the resiliency of the resin. Polyester based powder coatings are frequently used as top coats due to their exceptional chalk resistance.
Health & Safety
Powder coating isn’t just more durable than liquid paint—it is also safer to store and apply.
Liquid paint is hazardous for several reasons. First of all, it’s flammable. Careless storage can easily lead to a dangerous chemical fire. Wet paint is also a health hazard to the operators that work with it.
Wet paint emits volatile organic compounds (VOCs). Long term exposure to VOCs, especially in enclosed spaces, causes respiratory irritation and compounding health problems. VOCs are also a major source of industrial pollution.
Because powder coatings don’t contain any fluids to evaporate, they don’t emit any VOCs, and are completely free of the associate health and safety risks.
Powder coating is usually cheaper than wet paint in the long run, but the upfront costs tend to be higher. Wet paint technology has been around a lot longer (powder coating was developed in the 1950s), so the equipment and materials are more widely available.
The savings with powder coating are mostly indirect, but they add up fast.
First, powder coatings have a much better utilization rate. Unlike liquid paint, powder can be collected and reused. Approximately 70% of paint is lost to overspray during application, while material loss of powder coating can be kept under 5%.
Cost is also heavily effected by safety and environmental regulation. Because it is more hazardous, wet paint requires more investment in mitigation measures and insurance premiums. Powder coating facilities can keep these costs to a minimum.
Labor costs are also lower for powder coating. It doesn’t rely on highly trained operators. Powder coating can be done well by almost anyone, or even automated.
Finally, powder coating has much lower disposal costs. Less of it needs to be disposed due to the high utilization rate, and any amount that does need to be thrown away isn’t subject to the same tight environmental controls as paint.
New technological advancements and decreasing costs are driving up the popularity of powder coating, especially in industrial applications. While there will always be a role for liquid paint, you can expect to see more powder coating on the market in the future.