How to Sand Between Coats of Polyurethane for a Smooth Finish (220, 320, 400, 600 Grit Guide)

Applying polyurethane can protect wood and bring out its natural beauty—but without sanding between coats, you risk roughness, bubbles, or dust nibs ruining the finish. The secret to a silky-smooth surface is light sanding with the correct grits between layers. This guide shows how to sand between coats of polyurethane using 220, 320, 400, and 600 grit sandpaper.

Why Sand Between Coats?

Each coat of polyurethane raises the grain slightly and traps dust particles. Sanding removes these imperfections and gives the next layer a surface to grip. The result is a durable, professional-grade finish.

Recommended Tools

• 220–600 grit wet/dry sandpaper – the key for fine surface prep.
• Sanding sponge or block – keeps sanding pressure even.
• Tack cloth – removes fine dust between coats.
• Foam brush or lint-free applicator – applies polyurethane smoothly.
• Vacuum & microfiber cloths – essential for dust-free work.

Best Grits for Polyurethane Sanding

• 220 grit: First sanding after the initial coat.
• 320 grit: Standard grit between middle coats.
• 400 grit: For high-gloss or furniture-grade projects.
• 600 grit: Final sanding for ultra-smooth finishes before polishing.

Step-by-Step Process

1. Apply the first coat. Once dry, sand lightly with 220 grit (50-pack) to knock down raised grain.
2. Sand between coats. Use 320 grit (25-pack) for intermediate layers to smooth dust nibs and ensure adhesion.
3. For fine furniture finishes. Switch to 400 grit (100-pack) between final coats.
4. Final refinement. Before polishing or waxing, finish with 600 grit (25-pack) wet sanding for a silky, mirror-like surface.
5. Clean thoroughly. Always remove sanding dust with a tack cloth before applying the next coat.

Special Cases

For oil-based polyurethane, allow 24 hours before sanding. For water-based formulas, 6–8 hours is often enough. Avoid heavy sanding—just a light scuff is sufficient to promote bonding.

Pro Tips

• Sand gently—over-sanding may cut through previous coats.
• Always wet sand with 400–600 grit to reduce clogging and scratches.
• Use consistent strokes in the direction of the wood grain.
• Apply thin coats—thicker layers increase drying time and risk of imperfections.

Aftercare

• Let the final coat cure fully (at least 7 days) before heavy use.
• Buff with fine polishing compound if a mirror-like finish is desired.
• Maintain with gentle cleaners—avoid harsh chemicals that dull the shine.

FAQs

• Do I have to sand after the last coat? No, unless you want a super-smooth polished finish.
• What happens if I skip sanding between coats? You may get rough patches, poor adhesion, or uneven sheen.
• Can I use steel wool instead of sandpaper? Yes, but use synthetic pads on water-based polyurethane to prevent rust particles.

Watch & Learn

For a flawless polyurethane finish, stock the right grits. Explore the full fine grit sandpaper collection here.