Priming the Bodywork

Primer is a critical layer in a vehicle's decorative coating because it provides several benefits for the vehicle owner. Primer helps smooth the metal surface, resulting in a more appealing reflective appearance. It provides a cushion layer against the impact of road debris to reduce paint chipping. Finally, primer works with the coating layers above and below it to improve overall corrosion resistance, adhesion, and long-term weathering durability.

Primers come in various colors, typically black, grey, yellow and red. The color of the primer is important and selecting it will depend on the color of paint used. The primer color can affect the final color of the paint. There are also specific primers made for specific types of material. For example, aluminum, steel, plastic and fiberglass, each have primers designed to work with those specific surfaces. Using a primer made for aluminum on a steel surface may not provide the cohesiveness that is desired (it might peel).

Contrary to a lot of websites, it is recommended that you sand surfaces to at least 180-220 grit sandpaper before applying even a high-build primer. Some websites indicate that 80 grit is enough. While it initially appears enough, the sanding grooves left by 80 grit are too deep and the primer will not provide sufficient adhesion and will cause paint problems later on. Play it safe and go to 180-200 grit paper! Remember 90% of painting is body prep which includes bodywork and priming!

There are several different types of primers available:

  • Etching Primer

    This primer chemically protects against the corrosion process and contains an acid. It is a thin coat used on bare metal to prevent rusting. just used to prevent rusting. This doesn't mean that you can prime your car and then park it outside and it won't rust. This is a common misconception - the car may rust even faster! One of the functions of primers is to have the paint stick to it which means to allow the paint to be absorbed/bonded to the primer layer (to put it simply). Primer does this equally well with water! This means that if you primer your ride and leave it outside, it is NOT protected and it will RUST!

  • High-build/Surfacer Primer

    The high-build primer is generally used when the metal is a bit rough and you need a slight buildup to help cover scratches or pinholes or bodywork. It is a thick primer that has solids and is used to fill small imperfections and sanding marks. It is thick enough to provide a thickness that can be sanded or block sanded to a smooth base for paint.

  • Finishing Primer/Primer Sealer

    The finishing primer is thinner, dries fast and is generally used for surfaces that already has a smooth finish and it may be applied over the high-build primer for a smoother finish. You do not sand this primer, it is the last stage before painting. Application is the same, except the high-build needs more drying time between coats and before sanding.

You can purchase primer in aerosol cans or cans of paint that are used with a spray gun. For small areas, the spray cans will suffice. For larger areas and for finishing, you will want to use a spray gun to create a nice even finish. When using a spray gun, you may need a larger nozzle for high build primers due to the high build primers being thicker.

When you spray primer, the top spraying "tip" is to look at the reflection of the wet primer while spraying. Primer dries flat and provides little reflection except when you spray it. The reflection seen during spraying will show any surface irregularities that you may not be able to see when the primer is dry. The nice thing about primer is that it dries fast and you can quickly see and correct any faults in the bodywork before you proceed with painting.

On my 54 Pontiac, at this point I've stripped the paint and rough finished the roof chop. The car is in a rough primary and will need to be sanded and smoothed before any paint is applied. There is also the rusted rocker panels, rear quarter panels and trunk lip to be addressed not to mention the custom mods to be done.

front in primer

Here's the front in primer, the hood needs to have the channel filled yet.

ass end

Here's the rear end, you can see the rusted out sections quite well now.

Driver's door interior panel primed

Passenger's side door primed

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Copyright May 2011 Eugene Blanchard