Acrylic Enamel vs Acrylic Urethane
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I have always used acrylic enamel for my single stage jobs but recently I have tried acrylic urethane as well. What are the advantages and disadvantages of each? Why would you choose one over the other? Are there instances when one should be used instead of the other?
That is an excellent question!
The difference is the chemistry. They both have different binders (resins) that make up the base of the paint. The other parts of the paint (the pigmentation and the solvents) are not that different and in some product line, identical.
[b]Acrylic Enamel[/b] is an older technology where Acrylic Urethane is a little more modern, although both have been around for a long time.
Older Enamels cured through a process of oxidization. Basically, there would be no hardener/activator added. You reduce the product, spray it, then as air reacts with the binder in the paint they combine and change the chemical composition to become hard and durable. Even thought they have no activator they are considered a convertible coating (a product that changes chemically as it dries, and cannot be changed back). Acrylic Enamals are very similar but usually have a catalyst that helps to speed up the process as older enamels took a long time to fully cure. Acrylic Enamel catalyst is different from the hardener/activator used with urethanes. Some acrylic enamels, such as the Omni AE allow the option to use the catalyst or not use it.
[b]Acrylic Urethane[/b] became a new technology probably somewhere in the 1970s. Most all products today (basecoats, clear coats and industrial polyurethanes) are based on this technology. Urethane binders are divided into two parts: you have the base (resin in the paint) and the activator/hardener. When you mix the two together you start a chemical cross linking that makes a super hard/durable product that can be stronger and last longer than Enamel. Basically the resin contains a chemical called hydroxyl and the hardener contains isocyanide. The two chemicals are what combine to create a Polymer, through Polymerization which creates the strength of the paints. Polymers are also the base of all plastics. So technically urethane paints are a thin coat of hard durable plastic once cured.
So what does this mean for you? Urethane is probably a better choice for the long term. An advantage to the urethane, as well, is that as you spray it, the (clear) resin tends to come up to the surface quickly basically leaving a super thin clear coating over top of your pigment (similar to having a thin layer of clear coat). Most quality paints have some UV protection added to the resin, thus, the thin layer on top prevents UV degradation of the pigments and the paint much better than enamels, which is even more important when spraying metallic colours.
Basically what I would summarize with is that urethane is a newer technology that is generally more durable than enamel and therefore is likely a better choice. Many inexpensive paint lines (such as Limco, Omni and Nason) offer both AE and AU paints at similar prices, so if you have the choice go for the urethane even if it slightly more expensive. But as with anything, always compare apples to apples. A super inexpensive urethane may not be better than the worlds best acrylic enamel where there is some phenomenal price difference due to the quality of the products used to make the paints. However, you are unlikely to find much for quality acrylic enamels anymore and I am sure that in the next few years most paint manufacturers will completely stop making acrylic enamel paints.
Hope this might clear things up, and best of luck!
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