You may have noticed some boats have a checkerboard pattern within these painted surfaces. This is caused by a secondary cure resulting from painting a cored laminate black that leads to shrinkage and the core showing through. The three most important factors in getting a good result are preparation, preparation, and preparation. Seventy-five percent of the cost of painting involves preparation. Any paint job is only as good as the preparation that precedes it, and the skill of the people doing the work.
Improper preparation can only result in dissatisfaction and a failed paint job.
Old gel coats are often porous and may have absorbed years worth of waxes and oils, a condition that reduces the ability of new paint to adhere to the surface. Thorough dewaxing and sanding is needed to make sure that contaminates are removed. This is followed by special primer coats that improve adhesive properties. All surface irregularities must be smoothed out, old holes and scratches filled and carefully faired out. There's nothing like a fresh, glossy coat of new paint to show up surface defects.