Any experienced painter will tell you that the key to a great paint job starts with proper vehicle preparation.

Whether you’re repairing a chipped area or respraying the whole car, avoiding mistakes during the prepping process will make the job easier and quicker and result in a better finish.

Here are four common mistakes to avoid when preparing a car for painting.

1. Not preparing the surface correctly

Proper surface preparation is key to a great paint job. Sanding, applying body filler, and priming must be done correctly.

Follow the manufacturer’s recommendations when applying body filler and finishing it.

Use the correct grit of sandpaper. You want to final sand using 400-grit, not 600-grit, 800-grit, or 1000-grit. Be careful when sanding a blend panel — don’t sand too much or too little.

When applying primer, don’t make the mistake of priming over bad bodywork that has pinholes or imperfections. Also, be sure to prime over feathered areas.

2. Not cleaning the surface properly

Applying paint to a dirty surface will prevent it from adhering. You should wash the surface before sanding, using water and car soap. Next, apply a good grade solvent designed to remove grease, wax, tar, road grime, and other surface contaminants.

Remember to clean new panels with a solvent. Not doing so will result in contaminants getting sanded into the panel, which will show up as a blistered paint finish.

The solvent should be applied using a clean towel or rag saturated with the solution. Wipe it off using another clean towel, not shop rags that could be contaminated.

3. Over-reducing or under-reducing paint

Follow the manufacturer’s recommendations when reducing paint. The instructions are based on careful chemistry and calculations. Painters who ignore   manufacturer recommendations will end up with a less than optimal paint surface.

4. Contaminated paint area or spray area

Contaminants such as dust and dirt can be sucked into the paint booth through a crack and end up on the car. Operate your paint booth at a slightly positive pressure compared to the surrounding environment. Keep your filters clean and don’t use the booths for anything but painting.

Always wipe down all surfaces with a microfiber cloth before painting. This is especially important in open face booths, where it is easy to pull in contaminants from the shop.

Shop cleaners should be silicone-free. Some new cleaners claim to be silicone-free, yet they include an additive that reacts the same way as silicone. Using them can cause fisheyes in your finish.

Avoiding these four common mistakes will help you achieve a great paint finish.