How to Use a Block Sander on Primer

Before repainting your car's fender, prime and then sand.

Between priming and painting body parts on your car, you should use a block sander to get the primer surface ready. Sanding prepares the surface of the car after the primer for optimal adhesion of the top coats of paint.

Things You'll Need

• Sandpaper (180-grit or 220-grit)
• Sandpaper (400-grit)
• Air sander
• Primer surfacer

Instructions

1. Wait for the primer to completely dry after application. The specific time will vary based on conditions in your garage and the primer's manufacturer.

2. Apply primer surfacer to the entire area you're going to sand. This keeps the sander from taking away too much primer and shows you particular areas that may be rougher on the body than others.

3. Use the block sander with 180-grit or 220-grit sandpaper to start. Use vertical and diagonal strokes to sand. When you've covered the entire area, go back with 400-grit sandpaper to get rid of any rough areas. If you start to see metal through the paint, stop.

4. Add primer to fill scratches that appear during sanding. Return to Step 1 and start again. This may happen several times, but each time you should have fewer scratches.

5. Use an air sander with the lighter-grit paper to "feather" the surface into surfaces that still have all paint coats. This will make the line between painted parts and what you're repainting seamless.

References

• Autovations: Restoration Tech Tips
• YouTube: DIY - How to Block Sand Primer to Get Ready for Paint
• Welle Auto Supply: Block sanding