How to Sand Marine Gelcoat for Repair and Polishing (320–2000 Grit)

Boats and jet skis with fiberglass hulls rely on a gelcoat layer for shine and protection. Over time, this gelcoat can oxidize, scratch, or dull. Sanding is the key step in restoring gelcoat surfaces before buffing them back to brilliance.

Why Sand Gelcoat?

Gelcoat surfaces degrade from UV rays, saltwater, and abrasion. Sanding removes oxidation, smooths scratches, and preps the surface for polishing compounds or re-coating. Done correctly, sanding can bring back the original glossy look of your boat or watercraft.

Tools You’ll Need

• Dual-action (DA) sander or sanding block
• Respirator mask and eye protection
• Spray bottle or hose for wet sanding
• Microfiber cloths
• Wet/dry sandpaper sheets (320–2000 grit)
• Marine polishing compound & buffer

Recommended Grit Sequence

• 320 grit: Initial sanding to cut through heavy oxidation.
• 600 grit: Smoothing out 320-grit scratches.
• 1000 grit: Refining the surface for clarity.
• 1500 grit: Pre-polish sanding.
• 2000 grit: Ultra-fine finish before polishing compound.

Step-by-Step Process

1. Clean the hull. Wash thoroughly to remove salt, grime, and wax.
2. Start with 320 grit. Wet sand using 320 grit (25-pack) for oxidation removal.
3. Refine with 600 grit. Smooth the surface with 600 grit (10-pack) wet/dry sheets.
4. Polish with 1000 grit. Use 1000 grit (100-pack) to eliminate haze and prep for gloss.
5. Finish with 1500–2000 grit. Achieve an ultra-smooth surface ready for buffing.
6. Buff and polish. Apply marine compound with a buffer to restore deep shine.

Special Cases

For colored gelcoats, avoid starting too coarse—test with 600 grit first. For severely chalky surfaces, multiple passes may be required before polishing.

Pro Tips

• Always wet sand to control dust and heat.
• Work in small sections to avoid uneven sanding.
• Keep the sander moving—staying in one spot can thin the gelcoat.
• Seal with marine wax after polishing for UV protection.

Aftercare

• Rinse boat after every use to reduce salt buildup.
• Apply marine wax 2–3 times per season.
• Store covered or indoors to prolong gelcoat life.

FAQs

• Can I dry sand gelcoat? Not recommended—wet sanding keeps the surface cool and dust-free.
• Will sanding remove deep cracks? No—deep cracks require gelcoat repair filler.
• Do I need to re-coat after sanding? Not always—often, polishing after 2000 grit restores shine without recoating.

Watch & Learn

With the right sanding sequence, your boat’s gelcoat can look brand new again. Explore our medium sheets, fine grits, and ultra-fine papers to tackle any marine restoration project.