How to Sand Between Polyurethane Coats on Wood (320–600 Grit Guide)

A flawless wood finish requires more than just layers of polyurethane—it’s the sanding between coats that creates that smooth, glass-like surface. This guide explains how to sand polyurethane safely and effectively, from leveling imperfections to prepping for the final glossy coat.

Why Sanding Between Coats Matters

Each coat of polyurethane raises wood fibers and traps small dust particles. Sanding between coats flattens these imperfections and ensures better adhesion for subsequent layers. Without sanding, the finish can feel bumpy and may peel over time.

Recommended Tools

• Wet/dry sandpaper (320–600 grit range).
• Foam sanding pad or hand block.
• Vacuum and tack cloth for cleaning.
• Microfiber rags and high-quality brush or applicator.
• Good lighting for inspection.

Ideal Grit Sequence

• 320 grit – Lightly scuff the first coat to remove raised grain.
• 400 grit – Smooth the second coat for even texture.
• 600 grit – Final sanding before the last coat for silky gloss.

Step-by-Step: Sanding Between Polyurethane Coats

1. Let the coat cure. Wait until the surface is completely dry—typically 24 hours for oil-based, 6–8 for water-based polyurethane. Sanding too early can clog the paper and ruin the finish.
2. First sanding pass. Use 320 Grit (25-pack) wet/dry paper to level the first coat. Sand with light pressure along the grain until the surface feels uniformly smooth.
3. Clean the surface. Vacuum and wipe with a tack cloth to remove all sanding dust before reapplying polyurethane.
4. Apply the next coat. Brush or wipe on a thin, even coat. Let it dry, then inspect under raking light for nibs or streaks.
5. Second sanding pass. Use 400 Grit (50-pack) sandpaper to smooth the second coat and eliminate imperfections.
6. Final finish sanding. Before the last coat, gently sand with 600 Grit (100-pack) paper to achieve a silky-smooth surface. Avoid cutting through layers—use minimal pressure.
7. Apply final coat. Use long, overlapping strokes for consistent sheen. Avoid over-brushing to prevent bubbles or drag marks.

Special Cases

For high-gloss finishes, allow the final coat to cure for several days before buffing lightly with 1000–1500 grit wet/dry paper. For satin finishes, stop at 400 grit before applying the last layer. If you accidentally sand through, spot-touch with polyurethane and feather blend when dry.

Pro Tips

• Always sand in the direction of the wood grain.
• Use a soft touch—you're removing imperfections, not the coating itself.
• Keep sandpaper clean; polyurethane residue clogs grit quickly.
• Use good lighting—dust nibs and streaks show best under low-angle light.
• Thin coats dry smoother and need less sanding overall.

Aftercare

• Allow the final coat to cure 3–7 days before heavy use.
• Clean with a soft cloth and gentle cleaner—avoid ammonia products.
• Rebuff every few years with 1000 grit for refreshed shine.
• Maintain stable humidity to prevent cracking or hazing.

FAQs

• Do I always need to sand between coats? Yes, except if recoating within 2 hours on fast-drying products—always check manufacturer guidelines.
• Can I wet-sand polyurethane? Yes, but only after full cure—wet sanding too early can cloud the finish.
• What if I get bubbles in the finish? Let it dry, then sand smooth with 400 grit and apply a thin recoat.

Watch & Learn

By carefully sanding between polyurethane coats from 320 to 600 grit, you’ll achieve a perfectly smooth, professional finish that enhances your wood’s natural beauty and durability.