How to Sand Gelcoat on Boats for Repair and Polishing

Gelcoat protects fiberglass boats from water and UV damage, but over time it can fade, scratch, or crack. Sanding gelcoat is essential for repairs, refinishing, or polishing. Here’s a step-by-step guide to sanding gelcoat safely and effectively.

Why Sand Gelcoat?

Sanding removes oxidation, smooths scratches, and preps the surface for new gelcoat, paint, or polish. Without sanding, coatings won’t adhere properly, and imperfections will remain visible.

Tools You’ll Need

• 9x11 in wet/dry sandpaper sheets
• Orbital sander or sanding block
• Spray bottle with water
• Microfiber cloths
• Polishing compound or marine paint

Best Grit Sequence for Gelcoat

• 400 grit: Removes oxidation and surface damage.
• 800 grit: Smooths and levels scratches.
• 1500 grit: Pre-polish sanding for semi-gloss finish.
• 2000 grit: Refines for a near-gloss finish.
• 3000 grit: Ultra-fine sanding before buffing.

Step-by-Step: Sanding Gelcoat

1. Clean the surface. Wash thoroughly to remove salt, dirt, and oils.
2. Start with 400 grit. Use 400 grit (25-pack) to remove oxidation.
3. Smooth with 800 grit. Apply 800 grit (50-pack) for refining scratches.
4. Polish with 1500 grit. Use 1500 grit (100-pack) before final polishing.
5. Finish with 2000–3000 grit. Wet sand evenly for a mirror-ready finish.
6. Buff and polish. Use marine polish and a buffer for shine and protection.

Special Cases

For deep cracks or chips, repair with fresh gelcoat or resin before sanding. For light oxidation, start with 800 grit instead of 400.

Pro Tips

• Always wet sand gelcoat to prevent heat buildup and clogging.
• Sand in overlapping strokes for even results.
• Apply UV protectant after polishing to extend finish life.

Aftercare

• Wax or seal gelcoat regularly to maintain shine.
• Rinse with fresh water after each outing to reduce salt buildup.
• Re-polish annually or as needed depending on use.

FAQs

• Do I need to sand before reapplying gelcoat? Yes—sanding ensures proper adhesion.
• What grit before polishing? 1500–3000 grit gives the smoothest base.
• Can I sand gelcoat by hand? Yes, but power sanders save time on large areas.

Watch & Learn

Restore your boat’s finish with eQualle’s wet/dry sandpaper sheets, available in 25, 50, and 100 packs in grits 400–3000. Shop gelcoat sanding sheets here.