Epoxy Primer is used as a metal primer in automotive applications.
It improves adhesion of the paint to the steel and works to seal the steel from air and water in the fight against corrosion (rust).
I own a 2003 Chevrolet S10 pickup truck that had a rust issue on the lower corner of the drivers-side 3rd door. I had noticed bubbling on the corner of the door and ignored it for a while. The time finally came to address this problem.
To make the job easier I removed the door from the truck. This required me to remove four hinge pins. This door did not have any electrical connections with which to be concerned.
Once the door was off I checked the extent of the damage. A wire wheel on a grinder would remove the bubbled paint and expose the underlying metal.
The damage was much worse than I had anticipated, extending several inches across the panel.
My analysis quickly determined that the best course of action would require metal replacement. I purchased a repair panel to replace the entire lower portion of the door. The body side molding of the truck would hide the weld and paint seam.
Alignment marks were made on the existing door and the replacement panel. I cut out the old panel and matched it to the new panel so that both were the same size.
With the old metal removed I could get into the door to remove rust and repaint the steel with new primer and paint. I worked to prevent future problems by addressing existing rust problems inside the door and adding a layer of epoxy primer to prevent corrosion.
The new panel was carefully fitted to be as close to factory appearance as possible. The bottom edge of the door had not been attached by weld from the factory. I didn’t want to weld it this time so I used thickened epoxy resin to create a bond between the new panels.
The next step was to weld the sides of the panel into place while being careful to not warp the sheet metal of the door. I carefully stayed below the line of the top of the body side molding. I had marked this no-go area with tape.
With the welding completed I moved to making it look nice. Careful grinding of the weld removed excess material and smoothed the area.
Polyester filler “Bondo” is spread into the couple of small areas that would show around the body side molding. After curing, the filler was sanded and filled again until I created a smooth transition from the metal to the filler.
The area was cleaned before being sprayed with epoxy primer to seal the bare sheet metal and body filler. The epoxy primer was allowed to cure before being sanded and covered with 2K filling primer. This filler primer is thicker and easier to sand. This helps fill and small imperfections in the surface until everything is a smooth transition.
A final sanding of the primer was completed before the area was masked off and sprayed with sealer. This is the final coat before the paint and it helps to improve adhesion and to hide any discolorations.
The paint basecoat was applied over the door in even and overlapping coats. Clearcoat paint was sprayed on top of the basecoat, creating a smooth outer surface that will hold up to the extreme weather that will be encountered. This clearcoat is the first line of defense against UV, water, salt, and other chemicals that are confronted on the roadways.
I spray painted the inside of the repair with rust-preventative primer and a coat of paint. After allowing it to dry overnight, I added a coat of creeping oil for another layer of protection against corrosion.
Reinstallation of the door and the weatherstripping made the project complete. My truck again has a great looking door that will remain rust -free for years.