PUZZLED ABOUT PRIMERS? Here are tests you can duplicate TEST 1 —One coat of self-priming vinyl. Coating breaks away (L) due to severe undercutting (R), exposing metal to progressive corrosion.
CAUSTIC
TEST 2 —Epoxy primer, epoxy topcoat. Coating lifts off in single sheet (L) as adhesion fails (R), exposing entire surface to corrosion.
TEST 3—Oil primer, oil topcoat. Both coats fail completely (L) as underfilm caustic reacts on their oils to form soaps (R).
TEST 4—Amercoat's No. 86 inhibitive primer and No. 33HB vinyl topcoat. Corrosion restricted to scored line (L), no undercutting or peeling (R).
JLhe purpose of these accelerated tests is to show what happens when various types of coatings are exposed to a typical corrosive environment. Four clean steel panels, free from mill scale and rust, were coated with dif ferent combinations of primers and topcoats. Each was scribed to bare metal and immersed in salt water in the presence of free oxygen, for two weeks. As caustic deposits formed over cathodic areas of the steel in tests 1, 2 and 3, failure occurred in three ways. The vinyl, though not directly attacked, was undercut as caustic
spread beneath the film and destroyed adhesion. The epoxy coating, known for critical adhesion to smooth metal, proved impervious to caustic attack. It was, however, lifted in its entirety as moisture spread beneath the sur face. The entire oil paint film was quickly penetrated by the salt solu tion, creating widespread corrosion and caustic formation. The caustic then reacted with the oil to saponify the film. In the fourth test the corrosion was limited to the score mark. Reason: Amercoat No. 86 Primer resists un dercutting and adheres tenaciously,
inhibiting electrolytic corrosive action. The conclusions are clear. To pro vide long term protection in corro sive service, start with Amercoat No. 86 Primer, which provides a sound and lasting base for quality topcoats such as Amercoat No. 33HB. Write today for complete data on Amercoat No. 86, and have the de tails on hand when planning your next important coating job.
Amercoat®
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CORPORATION """-^— Ξ-*^1™ϋ^""-"'
"Dept. XE"
4809 Firestone Blvd., South Gate, Calif. VOL. 50, NO. 5
·
MAY 1958
19 A
