How to prep for spray paint gun work

Just as important as knowing how to use a spray gun is knowing how to prep your surface beforehand.

Before using a gravity feed spray gun or any other type of spray gun on your vehicle or panel, you need to ensure that the surface you’re working with is as clean and smooth as it can be. This is where prep work comes in. It’s a vital stage of auto refinishing.

How to prep for spray paint gun work

 Here we’ll talk about the key stages of panel preparation.

Sanding back + filling

Firstly, you’ll need to sand your surface. Sanding is done for two key reasons; to remove imperfections and to create adhesion as an abraded surface will hold the paint layer from your spray gun effectively.

An orbital sander is probably the best investment you can make for this purpose and ideally if you can use two, one small and one large for different areas, you’ll be even better off. In most cases, you’ll need to sand all the paint off until you reach the bare metal. Do this using light pressure with the orbital and making sure not to hold it at an angle or to keep it in one spot for too long, or you risk heating up and distorting the paint as well as making the surface uneven. An uneven surface means trouble once you get to the stage of using your paint spray gun.

For the dents and scratches on your surface, you’ll need to apply filler and there’s an art to this. Apply the filler to your board and then mix with downward sweeping movements to remove all the air bubbles and create a smooth texture.

Next fill in your dent. You can use a spatula or anything with a sharp flat edge. Some people even use a credit card! Apply your filler in smooth strokes and with multiple layers rather than one big blob as this will allow it to cure evenly and results in a much better finish. Usually, filler takes around five to 10 minutes to cure, but this can differ depending on the make. 

Levelling your repair area

Once your filler is cured, you’ll need to sand it back with paper and a sanding block. Start with coarser sandpaper and gradually move on to a finer grain, sanding multi-directionally and keeping your strokes as small as possible, so that you don’t over sand the surrounding area; and your aim should be to level the repair area with the surrounding area to enable your paint spray gun to do its best work. If you’re not happy that your surface is level, you can always apply more filler and repeat the process.

Sanding back your filled surface a little also once again creates an abraded surface that will hold the primer. 
Applying primer + sanding back

Next, mask off the repair spot ready for the application of primer. A tip here is not to make your masked area too small. Depending on the size of the repair spot, allow a generous surrounding area to avoid a too sharply defined border between your repair area and the rest of the panel.

There are many different kinds of primer on the market but the key is to choose one appropriate for direct to metal application. Primer is applied with a spray paint gun in a sweeping motion and you’ll usually need around three coats. Curing times on a primer vary widely, taking anything from an hour to a day depending on the primer you’re using, so check on your tech sheet. Once your primer is dry you’ll once again need to create a smooth surface by sanding back. At this stage, it’s useful to use what’s called a guide coat of graphite powder or darker paint over the top of your primer. This gives you a visual guide. Sand the area, using increasingly fine sandpaper until the guide coat has disappeared. You can then sand over the area, again using finer and finer sandpaper to smooth out the surface.

How to prep for spray paint gun work

Smoothing + finishing your panel ready for paint

This stage is about preparing your panel for painting with a gravity feed spray gun or your preferred style of gun, and there’s more than one way to do this. You might use a finishing disk on the orbital sander and go over the whole area panel. Another approach is to use pasting method where sanding paste is applied to totally clean and smooth out your surface. You may even prefer to smooth your panel with find sandpaper by hand. An optional next step is to apply a sealer, which is like another smoothing primer to give a good foundation for your paint. It improves the quality of your finish in some cases but may not always be necessary.

Orientation coat

You will then need to apply an orientation coat. A good method is to use a solvent based toner from the same manufacturers as your paint. The orientation coat is essentially a binder that you’ll use to smooth your surface and fill in all the micro scratches on your panel. This is especially important if you’re using a light colour or metallic paint, so the paint particles won’t get caught in minor scratches and catch the light or stand out. Your panel is now ready for the first application coat of colour from your paint spray gun.


Please note the information provided in this website is General Information only, please read all product data sheets and safety data sheets before commencing any work. If pain persists show a professional.