Sanding Fiberglass: Smooth Repairs and Polished Surfaces

Fiberglass is strong and lightweight, making it ideal for boats, cars, and home projects. However, sanding is essential for repairs, refinishing, or preparing surfaces for paint or gel coat. This guide explains the grit sequence, tools, and techniques to sand fiberglass safely and effectively.

Why Sand Fiberglass?

Sanding removes rough edges, levels repairs, and preps the surface for coatings. Without sanding, paint and gel coat may not adhere, and repairs may remain visible. Proper sanding also ensures a smooth, professional-looking finish.

Tools You’ll Need

• Silicon carbide wet/dry sandpaper sheets (80–2000 grit)
• Sanding block or orbital sander
• Respirator, gloves, and goggles
• Vacuum or tack cloth
• Polishing compound (for finishing)

Recommended Grit Sequence

• 80 grit: Heavy shaping or stripping damaged fiberglass.
• 120 grit: Smooth repairs after coarse sanding.
• 220 grit: Prep for primer or gel coat.
• 600 grit: Refine scratches before polishing.
• 1500–2000 grit: Final wet sanding for glossy finish.

Step-by-Step: Sanding Fiberglass

1. Wear protection. Fiberglass dust is hazardous—always use a respirator and gloves.
2. Start coarse with 80 grit. Use 80 grit (25-pack) to strip damaged areas.
3. Smooth with 120 grit. Switch to 120 grit (50-pack) for even shaping.
4. Refine with 220 grit. Use 220 grit (100-pack) before coating.
5. Finish sanding. Progress to 600 grit, then wet sand with 1500–2000 grit for a polished surface.
6. Polish and coat. Apply polishing compound or gel coat for protection and shine.

Special Cases

For boat hulls, use coarser grits (80–120) to remove oxidation before progressing finer. For auto fiberglass panels, stick to 220–600 grit before priming. Always wet sand fine grits to avoid clogging.

Pro Tips

• Always sand in stages—don’t skip grits.
• Wet sanding keeps surfaces cool and dust-free.
• Check progress often to avoid sanding through fiberglass layers.

Aftercare

• Seal fiberglass with gel coat or paint to protect against UV and moisture.
• Polish regularly for lasting shine.
• Repair chips promptly to prevent deeper damage.

FAQs

• Can I dry sand fiberglass? Yes, but wet sanding is safer and reduces dust.
• Do I need special sandpaper? Yes, silicon carbide wet/dry sheets work best.
• What grit before paint? 220 grit provides the best adhesion for primers and paints.

Watch & Learn

Sanding fiberglass properly ensures smooth, durable, and polished results. Stock up on wet/dry silicon carbide sandpaper sheets—packs of 25, 50, and 100 available across all grits. Shop fiberglass sanding sheets here.