Study concludes that pre-painted metal parts are effective against corrosion.

CLEVELAND - Pre-painted metal parts should provide a superior, cost-effective product in corrosion and durability, compared with parts painted using other paint-application methods, according to the National Coil Coating Association.

The NCCA, along with the help of PPG Industries and the North American Zinc-Aluminum Coaters Association, set out to compare the corrosion resistance of pre-painted metal louvers on air-conditioning units to those coated with three types of post paint.

Pre-painted louvers with exposed cut edges were tested in the field along side three sets of metal louvers, one with a post-painted "electrocoat," a process where electricity is used to apply the paint, a second with a powder finish and a third with a spray finish. The parts in all instances were made of hot-dipped galvanized steel and louvers were exposed to the same environment in Daytona Beach, Fla.

Comparisons made after 16, 44 and 68 months of exposure to the elements showed pre-painted parts were repeatedly and significantly better than the post-painted parts in terms of the corrosion resistance, uniformity or treatment and film thickness, according to NCCA.

The reason that the pre-painted parts outperformed each of those with a post-painted application is because pre-painted metal sheet is uniformly cleaned, pretreated and painted as a flat surface, so the edge-to-edge and side-to-side variances are virtually eliminated.

In addition, the pre-painted parts has two coats of paint, tightly bonded to the metal as compared to post-painted parts, which generally has only one coat of paint.

The study found that in most cases, the pre-painted part has paint on the backside as compared to the post-painted part, which at best has minimal amount of overspray. Uniform pretreatment and paint on the backside of a part increases the corrosion resistance of the part, enhancing long-term durability, officials said.