Although this step is not absolutely necessary, it is certainly a good idea if you want to achieve a really good result. Also I wouldn’t recommend doing this with ordinary primer/surfacer as it is usually not thick enough to rub back.
The first step is to grab yourself a pressure-pack can or tin of black acrylic if you don’t mind using the spray gun again.
Usually a decent sized pressure pack can will be sufficient for most cars, just be sure it is acrylic not enamel as enamel will react with the top coat acrylic if there is even the smallest trace of it on the panel.
The next step is to spray a light coat across your panels. Read the instructions and allow enough drying time before sanding.
For the next step I use 800-1000 grit wet and dry paper used wet and with a sanding block. Once again you want to follow the lines of the panel and keep plenty of water on the surface. As you can see (hopefully!) from the pictures some of the repairs that we did are far from perfect and although the door looked good these imperfections would have showed up after the top coat was on. Hence the reason to use a guide coat!
The beauty of high-fill primer is that 99 percent of the time you can sand out these imperfections without the need for more filler or reaching the bare surface below. Be extra careful at the edges of the panels as it is easy to sand through the primer there and as with the speed file, don’t be tempted just to sand one little area to get rid of all the guidecoat, keep the sanding block moving across a large area until all the guide coat is gone. If you do happen to sand through the primer it is simple a matter of applying some more primer and a guidecoat to the area and sanding again.
Once you think you have sanded the entire panel wash it down with clean water and check for any remaining guide coat, re-do any problem areas and finally either dry the panel with compressed air or leave it out in the sun for an hour or two.
An important note regarding primer – 99 percent of primer/surfacers, spray putties etc are porous meaning that they will absorb moisture. The amount of time between applying the primer and the top coat should be as little as possible and once the wet sanding is finished be sure to dry the panel down as much as possible. Any moisture trapped in the primer has the ability to ruin our nice new paint job. Not good!
Part Seven is finally done – Click Here.