Boat Fiberglass Restoration: 400?800?1500?3000 Grit Sequence

Boat hulls and fiberglass decks fade, chalk, or scratch from sun and water. The way to revive gloss is progressive wet sanding: 400 ? 800 ? 1500 ? 3000 grit, followed by compound and wax. This removes oxidation, smooths the gelcoat, and restores shine that lasts.

Why Wet Sand Fiberglass

UV and salt degrade gelcoat, leaving dull, porous surfaces. Compounding alone can’t cut through heavy oxidation; sanding levels the gelcoat first. Each grit step reduces scratches until surface is ready to polish. Finish protects hull and keeps it slick in water.

Tools & Materials

• 9×11 in wet/dry sandpaper sheets: 400, 800, 1500, 3000 grit
• Orbital sander with foam pad or hand block
• Spray bottle with water + soap
• Marine compound and polish
• Wax or ceramic coating
• Microfiber towels
• PPE: gloves, respirator, eye protection

Recommended Grit Sequence

• 400 grit — Removes chalky oxidation, levels surface.
• 800 grit — Refines 400 scratches, begins clarity.
• 1500 grit — Smooths to satin, reduces haze.
• 3000 grit — Pre-polish finish before compound.

Step-by-Step: Boat Fiberglass Restoration

1. Wash hull. Clean thoroughly with boat soap. Salt or grit left behind scratches.
2. Sand at 400 grit. Using 400 grit (25-pack), wet-sand until chalk and oxidation disappear.
3. Step to 800 grit. Switch to 800 grit (50-pack). Sand evenly until surface looks smoother.
4. Refine at 1500 grit. Move to 1500 grit (100-pack). Work until surface feels silky.
5. Final pass at 3000 grit. Finish with 3000 grit (25-pack). Sand lightly until hull has satin sheen.
6. Compound. Buff with marine compound to remove final haze.
7. Polish & wax. Apply polish, then marine wax or ceramic coating to protect gloss.

Special Cases

Severe oxidation: Start at 220 grit before 400 ? 800 ? 1500 ? 3000.
Colored hulls: Require more care—dull spots show faster.
Decks: Use nonslip-safe cleaners—don’t oversand textured areas.

Pro Tips

• Keep surface wet—dry sanding burns gelcoat.
• Sand evenly in long strokes—avoid wavy spots.
• Replace paper often—oxidation clogs quickly.
• Buff in shade—heat reduces compound effectiveness.
• Seal annually to lock in gloss.

Aftercare

• Wash boat with pH-neutral soap after outings.
• Wax every 6–12 months.
• Spot polish with 3000 grit and compound if dull patches return.

FAQs

• Can I skip to compound? No—oxidation is too deep for polish alone.
• Why stop at 3000? Beyond this, compound achieves full gloss more efficiently.
• Does sanding thin gelcoat? Slightly—work evenly, only enough to remove oxidation.
• Do I need wax? Yes—wax or ceramic protects finish from UV and salt.

Video: Fiberglass Sanding & Buffing

Closing: Boats shine again with proper sanding. Follow 400 ? 800 ? 1500 ? 3000 grit, then compound and wax, to restore fiberglass hulls and decks to their original luster.