What Is Self-Etching Primer?by Tom Lutzenberger
Anyone who has had to paint metal knows that the first step is to strip off the old paint, or at least cover it with primer so that the new coat will adhere properly. For parts that need to be stripped down to the metal surface, etching helps new paint stay on instead of peel off when dried. Self-etching primer combines the two-step process of etching and primer into one chemical.
How it Works
For parts that will be painted again with enamel-based paints, etching-primer is applied right after the metal part has been completely stripped of old paint and dirt. This not only protects the metal from flash rust due to oxidation, but also prepares the surface for the final paint coat. The primer itself includes acid and zinc as the operative elements. The acid burns into the metal chemically and the zinc applies a seal. For the etching process to work correctly, the metal must be completely bare so that all oil residue and previous paint can be removed.
Any rust on metal parts must be removed first either by sanding, media blasting or brushing off with metal brushes. Self-etching primer will not get rid of the rust; it will only paint over it. This will stop corrosion expansion until the area once again gets exposed to moisture and air.
Buying the Primer
Self-etching primer frequently comes in a gray color, similar to other primer paint. The tell-tale feature will be on the description of the paint container, specifically identifying the self-etching feature included in the paint. The most common paint type comes in a spray can version, which is the easiest to apply.
The application does not require multiple coats. One coat is enough since the secondary and final coats of paint will provide the actual outer surface. For metal parts with nicks, dents, and scratches, Bondo or similar filler needs to be applied and sanded down first to provide a smoother surface for the primer application. The self-etching chemicals will not affect the Bondo filler once it is dried onto the metal.
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