Ask the Expert: For fleet refinishing, will using 50 grit sanding improve my paint adhesion?

Q: For fleet refinishing, will using 50-grit sanding improve my paint adhesion?

Dan Szczepanik, Global Product Manager - Fleet & Manufacturing, Sherwin-Williams Automotive Finishes: One would think that using a very aggressive sandpaper will provide a rough surface for the paint to adhere to and be a better prep than using 320 grit. One would be wrong. When it comes to ideal preparation of metal when sanding, the depth of the scratches is less important than the frequency of the scratches on the surface. 50 grit has many fewer abrasive particles on the sandpaper than 320 grit, but what it does have is much larger abrasive particles than 320 grit. This provides few, deep scratches and is not the best for paint adhesion. Adhesion studies have revealed the ideal abrasives are between 180 and 400 grit, with most operations using 220-320 grit. These sandpaper grits provide the optimum blend between frequency of scratches and depth of scratches, which is the best surface for today’s primers for adhesion.

Information provided by: Sherwin-Williams Automotive Finishes