How to Sand Marine Gelcoat for Repairs & Refinishing

Boat hulls and other fiberglass marine surfaces are coated with gelcoat for protection and shine. Over time, UV exposure, scratches, and oxidation dull the finish. Sanding is the first step in restoring or repairing gelcoat, ensuring smoothness and adhesion for polishing or repainting.

Why Sand Gelcoat?

Gelcoat is durable but prone to surface oxidation, chalking, and scratches. Sanding removes the damaged layer, smooths repairs, and prepares the surface for polishing, waxing, or repainting. Without sanding, restoration products can’t penetrate effectively.

Tools You’ll Need

• Random orbital sander or sanding block
• Bucket of clean water (for wet sanding)
• Microfiber towels
• Marine-safe polishing compound
• Silicon carbide wet/dry sandpaper sheets

Best Grit Sequence for Gelcoat Sanding

• 600 grit: Removing oxidation and leveling repairs.
• 800 grit: Refining surface and preparing for finer sanding.
• 1200 grit: Smoothing scratches for a semi-gloss finish.
• 2000 grit: Final sanding before polishing.
• 3000 grit: Ultra-fine prep for mirror-like gloss.

Step-by-Step: Sanding Marine Gelcoat

1. Start with 600 grit. Wet sand using 600 grit (25-pack) to remove oxidation and level patch repairs.
2. Smooth with 800 grit. Use 800 grit (25-pack) to refine scratches.
3. Refine with 1200 grit. Switch to 1200 grit (25-pack) for improved clarity.
4. Polish with 2000 grit. Sand lightly with 2000 grit (100-pack) to prepare for polishing compounds.
5. Finish with 3000 grit. Use 3000 grit (50-pack) to achieve a high-gloss surface.
6. Buff & seal. Apply a marine polish and UV-protective wax to maintain shine.

Special Cases

For deep scratches or gouges, start at 400 grit before working up. For lightly oxidized gelcoat, you may begin at 800 grit. Always use plenty of water to avoid clogging sandpaper.

Pro Tips

• Work in small sections to maintain control.
• Use circular motions for even sanding.
• Keep sandpaper flat to avoid gouging the gelcoat.

Aftercare

• Reapply marine wax every season for protection.
• Rinse hulls after each use to prevent salt buildup.
• Store leftover sandpaper in a dry, sealed bag.

FAQs

• Can I sand gelcoat by hand? Yes—use a sanding block for small areas. For large hulls, a random orbital sander saves time.
• Do I need to polish after sanding? Absolutely—polishing restores gloss and seals the surface.

Watch & Learn

Proper sanding makes gelcoat restoration easier and longer-lasting. Shop our marine sanding collection for the right grits to keep your boat looking its best.