Powder Coating vs. Paint: Comparing Metal Finishes

Finishing is the final process in the manufacturing of many metal parts. Finishing makes parts look good, but it also protects them from corrosion, extending their shelf life and reducing maintenance. Painting and powder coating are two of the most widely used finishing techniques.

Both finishes coat the part in a layer that keeps moisture and oxygen from the substrate; however, they are made of different ingredients and applied using different processes. Each has strengths and weaknesses that impact its suitability for particular applications.

Powder coating is a dry finishing process. A powder is electrostatically applied to a surface and heated. The powder melts and flows together to form a thick, durable finish.

The powder is made of polymer resins, pigments, leveling agents, flow modifiers, and other ingredients. These are melted, mixed, and allowed to cool and solidify. The solid is then ground into a powder ready for application.

Powder coating is often applied through electrostatic spray deposition, although there are other techniques. First, the part is thoroughly cleaned to remove oils, moisture, and other contaminants. Then, the powder is applied via a spray gun. While it travels through the spray gun, it is given an electrostatic (negative) charge. The part to be coated is grounded, so the charged powder is attracted to it. The powder sticks to the part, quickly forming an even layer.

The parts are moved to a curing oven, where heat melts the powder. It flows together and reacts chemically to form molecular chains, providing a hard, durable protective coating.

While spraying is a widely used powder coating technique, parts can also be powder coated by fluidized bed coating. Fluidization forces air through a bed of powder, causing it to behave like a liquid or gas. The parts are heated and then dipped into the fluidized powder, causing the powder to melt and adhere to the part.

In contrast to powder coating, paint is a liquid mixture of ingredients that typically include pigments, solvents, and binders. Pigments provide the color, and binders hold the pigments together and help them to form a film on an object's surface. The solvent is a liquid — often oil or water‑based — that allows the paint to be applied more easily. As the solvent evaporates, the paint forms a hard layer.

Paint can be applied with brushes, but in industrial scenarios, it is almost always applied with a pneumatic spray gun. Spraying is faster, more efficient, and can be automated on high‑volume production lines. Additionally, spraying provides an even and uniform coating with a superior finish.

Powder coating applied by electrostatic deposition is best suited to metals. Metals can be grounded, which is essential to attracting the electrostatically charged powder. Metals are also better able to endure the high temperatures required for curing.

Non‑conductive parts can be powder coated, but not electrostatically. The powder would just fall on the floor. To powder coat materials such as plastic, glass, or wood, they must first be heated so that the powder melts on contact and sticks to the surface.

Neither powder coating technique is suitable for materials that are damaged by heating, including many plastics.

Powder coating does not rust, and it is excellent at protecting metal surfaces from rusting. Powder coat finishes resist peeling, cracking, chipping, and chemical exposure. Provided the coating is not damaged and has been applied to an appropriately prepared substrate, the underlying metal is safe from corrosion — improperly prepared substrates may cause flaking, bubbling, and peeling. However, no finish is indestructible even when it is applied correctly, and damage may allow water and moisture to penetrate. Once rust begins to form, it may spread and damage the finish in adjacent areas.

Powder coat finishes are more durable than painted finishes. Powder coating can protect metal for as long as two decades. However, exposure to moisture, UV, and heat degrades both finishes over time in a process called chalking. Chalking occurs at different rates depending on the environment the part is exposed to. An outdoor environment causes faster chalking, particularly if the part is in direct sunlight or exposed to harsh weather.

The quality of the powder and paint used also impacts their life cycle. More expensive UV‑resistant paints and powders retain their color and protective capabilities for longer than less durable alternatives.

Powder coating generally provides a thicker, more damage‑resistant finish that needs less maintenance than painted finishes. It is, however, more expensive, and it is not appropriate for parts that require thin finishes. On the other hand, paint is sufficiently durable for many applications, components can easily be repainted in the field, and painting is inexpensive compared to powder coating.

Finish thickness in the U.S. is measured in "mils," which are equivalent to a thousandth of an inch or about 0.025 mm. Powder coating thickness varies depending on the application, but between 2.5 and 3 mils is a typical minimum, rising to 6 mils and more for applications that require additional protection. Paint's thickness varies with the type of paint and the number of coats, but between 1 and 2 mils per coat is a reasonable estimate. If thinner finishes are desired, galvanization or conversion coating may be a better option, as discussed below.

Before choosing a powder‑coated finish or a painted finish for your parts, consider the durability, appearance, maintenance, thickness tolerances, and cost requirements on a case‑by‑case basis.

Painting and powder coating are popular finishes for metal parts, but there are many other finishes worth considering. They include:

Huyett manufactures and stocks a wide variety of parts available in many different finishes, including:

We offer a comprehensive range of secondary processes to help customers achieve their part finishing objectives, including painting, powder coating, conversion coating, galvanization, and more. Learn more about Huyett finishing processes in our guide to secondary processes or contact our expert Sales Team.