CAUSES: Slight ridges in dry paint film often are due to poor-quality applicators. If the polyester or nylon filament of a brush is not finished properly, it will leave marks. Other causes include a too-porous surface that absorbs too much coating, excessive brushing, applying too little paint, using the wrong type thinner or not allowing enough drying time between coats. Brush marks will occur in paint films that dry too rapidly.
SOLUTIONS: Always use top-quality applicators. Brushes should have tapered bristles properly flagged and tipped.
Smooth the surface by sanding before repainting, or the brush marks will show through the new coat. If the surface is porous, a primer should be applied. Be sure to use a recommended thinner if the coating is too thick, and allow the paint to dry completely between coats.
To make sure improper brushing is not the cause, ask your local independent dealer to demonstrate correct brushing techniques.