Should you prime a car before painting?

Primer is the most loved and feared word in the automotive do it yourself lexicon. Maybe that’s an exaggeration, but speaking of primer conjures up all sort of images, and depending on who you’re talking to these can range from heaven to horror. 

If you aren’t familiar with primer, here’s a primer. Primer is paint, but not in the way that paint is paint. Paint is paint because it creates an enduring and beautiful covering for your car’s body. Primer is paint only because it goes on the car and does have some tone of color. Their purposes are vastly different, but in many cases, one can’t survive without the other. 

Primer is a bonding agent. This means that primer enables a bond between the surface underneath it and the paint that will be sprayed on top. You want your paint to be strong and adhere well to the surface below it, so you should always apply a coat of primer before you paint, correct? Not necessarily. There are times when primer is very important, times when it is of little importance and even times when it could have an adverse effect on the job you’re trying to finish. 

Benefits of Primer, or When You Should Use Primer

As mentioned above, primer is the bonding agent, the glue, between whatever’s below it and your car’s paint. When your car was new, it was a beautifully welded patchwork of fresh steel panels and parts. This virgin metal, if painted naked, would eventually reject the paint so carefully sprayed on it and quickly rust, turning a brand new car into junk in no time at all. The same is true with any bare metal, new or not. Any time you do bodywork on your car, you are likely to uncover bare metal.

In most cases, you should get down to bare metal, like when you’re working with body filler, for instance. Sanding your repaired area to bare metal ensures that you’ll have a reliable repair that will last much longer than the parking lot job that just slapped a patch over the damage. Some coats of a good primer will make it even stronger. Any time you sand away from your vehicle’s paint and expose bare metal, you should apply primer before you paint, sanding lightly between coats to be sure you’ve got a smooth surface every time. 

When Don’t You Need Primer? 

There are lots of car people who will say that a coat of primer is worth applying 100% of the time before you spray your final paint coats. I disagree. Primer is very valuable in most cases, but if you’re completing a very small repair involving minimal molestation of your car’s sheet metal, primer may be overkill. Worse than that, it could make your repair harder to complete. Consider a small repair that was not sanded to bare metal. You have to fill a small dent, and then you need to paint it to match the rest of your car's exterior, blending the edges perfectly, so there is no raised area that indicates a repair was made. The smaller the repair area, the tougher it can be. Sometimes two coats of primer can raise the repair area enough to make it far more difficult to hide well.

Another time you don't need primer is when bare metal is not exposed at all. This includes bare plastic! And considering what percentage of minor damage happens to bumpers, and the fact that most bumpers today are plastic, you can skip the primer step without much worry at all. For larger repairs, you may need to order your paint with a flex agent mixed in.

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