How to Sand Fiberglass for Paint or Gelcoat: Essential Tips for Smooth Finishes

Fiberglass surfaces, whether on boats, cars, or outdoor equipment, require careful sanding to ensure paint or gelcoat adheres properly. This SEO-optimized guide covers the best sandpaper grits and techniques to sand fiberglass effectively—preventing scratches and preparing a perfect base for finishing.

Why Sand Fiberglass?

Sanding removes surface imperfections, oxidation, and prepares the gelcoat or resin for new coatings. Proper sanding avoids peeling, bubbling, or uneven color.

Best Sandpaper Grits for Fiberglass

• 80–120 grit sandpaper: For initial rough sanding and smoothing out imperfections.
• 180–220 grit sandpaper: For smoothing and feathering edges.
• 320–400 grit sandpaper: For final sanding before applying primer or paint.

Step-by-Step: How to Sand Fiberglass

1. Wear protective gear—fiberglass dust can irritate skin and lungs.
2. Start sanding with 80–120 grit to level rough areas and remove oxidation.
3. Use 180–220 grit to smooth transitions and feather edges.
4. Finish with 320–400 grit for a smooth, paint-ready surface.
5. Clean the surface thoroughly to remove all dust before painting.

Pro Tips for Fiberglass Sanding

• Wet sanding is recommended to reduce dust and heat buildup.
• Use a sanding block for flat areas and hand-sand curves and edges.
• Replace sandpaper frequently for effective cutting.

FAQs

• Can I use power tools to sand fiberglass? Yes, but use variable speed and light pressure to avoid damaging the surface.
• Is wet sanding necessary? It's recommended for dust control and smoother finishes.

Watch & Learn

Shop the best sandpaper for fiberglass at eQualle and find more marine and automotive finishing tips on our DIY blog.