Do it yourself painting can be a rewarding experience that can save you money in the long run, as long as you're prepared to put in the work. To ensure that your car comes out looking like it's supposed to, make sure that you're using the right kind of primer.
What Is Self-Etching Primer?
Apply self-etching primer as a base coat. This will give the paint a texture to grip on to. Self-etching primer is a primer that can come in an array of mixtures including a compound mixture that you have to mix yourself. It is also sold as an aerosol mixture, which can be used as simply as spray paint. Self-etching primers can be used on anything from steel or stainless steel, to aluminum, fiberglass or plastic.
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How Are They Used?
Wash and dry your metal before application. Apply primer only to a freshly cleaned surface. Most of the time self-etching primer is primarily intended for unprimed metals. Self-etching primer is a lacquer paint mixed with sulfuric acid. Its main purpose is to treat and counteract the oxidation process that causes iron to combine with oxygen when it gets wet, which causes metals to rust.
Acid Paint Primer?
Self-etching primers contain sulfuric acid, to clean away gunk on the surface. For this reason, self-etching primers are not recommended over clear coat finishes or existing paint. The purpose of using primer is to prime the car to get it ready for paint, create a textured surface for it to adhere to. You will be anything but ready for more paint if you use a self-etching primer on the existing surface as it will likely cause the edges to come up.
Metal Only
Use self-etching primers on metal surfaces only. The sulfuric acid in these mixtures can cause undesirable affects to the existing paint job. When applied to paint they can cause chipping and corrosion to the existing paint surface. This will require sanding as well as a fair amount of grunt work just to get the car ready to be primed again. For this reason you should not use self-etching primer on existing paint or gloss finish.
Alternatives
For a better finish over the existing painted surface, try using a pyroxylin or epoxy primer. Pyroxylin primers have been around at least as long as Ford's Model T, and are still used by some today, though it can be difficult to find the right mixture. Epoxy primers are considered by many to be the new standard as they can be used on metal or existing paint. Simply spray on, wait 30 minutes and sand if necessary.