How to Sand Between Coats of Polyurethane (320, 400, 600 Grit Step-by-Step Guide)

Polyurethane provides a tough, protective finish for wood furniture, floors, and trim. But to achieve a silky-smooth surface, sanding between coats is essential. Each coat of polyurethane raises tiny fibers and leaves behind dust nibs or bubbles. By sanding properly with 320, 400, and 600 grit sandpaper, you can create a flawless finish that feels as good as it looks.

Why Sand Between Coats of Polyurethane

Skipping this step often results in a rough texture, uneven sheen, or surface imperfections. Sanding ensures that each layer bonds tightly with the next while removing bumps for a smooth, professional look.

Benefits of sanding between coats:

• Improves adhesion: Creates microscopic scratches that help the next coat bond better.
• Smooths texture: Eliminates dust particles and brush strokes.
• Enhances durability: Multiple coats bond strongly for long-lasting protection.
• Silky finish: Achieves that hand-rubbed, professional feel.

Choosing the Right Grits

• 320 grit: Removes bubbles, dust nibs, and raised fibers after the first coat.
• 400 grit: Refines the surface and smooths out imperfections between later coats.
• 600 grit: Provides the final sanding pass for an ultra-smooth, glass-like finish.

Tools and Materials You’ll Need

• Sandpaper sheets: Reliable wet/dry sheets in 320, 400, and 600 grits.
• Sanding block: Helps maintain even pressure on flat surfaces.
• Vacuum or tack cloth: Removes fine dust before recoating.
• Foam brush or applicator: For applying smooth, even coats of polyurethane.
• Clean microfiber cloth: Wipes surfaces dust-free.

Step-by-Step Sanding Between Coats

1. First sanding (320 grit). After the first coat dries, sand lightly with 320 grit (25-pack) to remove dust and raised grain. Wipe clean with a tack cloth.
2. Second sanding (400 grit). Once the second coat cures, use 400 grit (100-pack) to smooth out bubbles or uneven sheen. Clean thoroughly before recoating.
3. Final sanding (600 grit). Before the last coat, finish with 600 grit (25-pack). Sand lightly for a silky, touchable surface that’s ready for the final layer.

Special Considerations

Water-based polyurethane: Dries faster and usually requires finer sanding between coats.

Oil-based polyurethane: Longer drying time but sands more easily—be patient before sanding.

High-traffic surfaces: Apply at least three coats with sanding in between for maximum durability.

Pro Tips

• Sand lightly—just enough to dull the sheen, not remove the finish.
• Always sand with the grain to avoid scratches.
• Use a vacuum plus tack cloth for complete dust removal before recoating.
• Allow proper drying time before sanding to prevent clogging the paper.
• For the final coat, skip sanding and let the polyurethane cure to a natural gloss.

Aftercare Once Finished

• Allow polyurethane to cure fully (up to 30 days) before heavy use.
• Clean surfaces with a damp cloth—avoid harsh chemicals.
• For extra smoothness, rub out the final coat with 0000 steel wool and paste wax.

FAQs

• Do I need to sand after the final coat? Not unless you want an ultra-flat matte finish. Most projects are complete after the last coat cures.
• Can I skip 600 grit? Yes, but 600 grit ensures the smoothest professional finish.
• What happens if I don’t sand between coats? Coats may not bond properly, leading to peeling or uneven finish.
• How many coats are best? Typically 3–4 coats for furniture, 5+ for high-traffic floors.

Watch & Learn

Shop polyurethane sanding sheets: Get 320, 400, and 600 grit sandpaper in convenient packs. Shop fine grit sandpaper.

Closing Thoughts

Sanding between coats of polyurethane may seem tedious, but it’s the secret to a flawless finish. By working through 320 → 400 → 600 grits, you’ll eliminate imperfections and create a silky-smooth surface that enhances the beauty and durability of your wood projects. With patience and the right sanding sequence, your finish will rival professional results.