How to Sand Between Coats of Polyurethane for a Flawless Finish (320–600 Grit Guide)

pplying polyurethane protects wood surfaces and brings out a rich, glossy look. But to achieve a glass-smooth finish, sanding between coats is essential. This process levels out dust nibs, bubbles, and brush marks, ensuring each coat bonds better and looks more professional.

Why Sand Between Polyurethane Coats?

Even in dust-free environments, small particles settle on wet polyurethane. Sanding removes imperfections and creates microscopic scratches that help the next coat adhere. Skipping this step often results in uneven sheen or peeling over time.

Best Sandpaper Grits for Polyurethane

• 320 grit: First pass between coats for light smoothing.
• 400 grit: Leveling brush marks or small bubbles.
• 500–600 grit: Final passes before the last coat for silky smoothness.

Tools You’ll Need

• Wet/dry sandpaper sheets (320–600 grit).
• Sanding block or pad for even pressure.
• Tack cloth or microfiber rag.
• Vacuum for dust removal.

Step-by-Step: Sanding Between Polyurethane Coats

1. Allow coat to dry fully. Wait 24 hours or follow manufacturer’s instructions.
2. Start with 320 grit. Use 320 grit (25-pack) to lightly smooth the cured coat.
3. Refine with 400 grit. Switch to 400 grit (100-pack) if you notice brush strokes or rough spots.
4. Finish with 600 grit. For the last sanding before the final coat, use 600 grit (50-pack) for a silky feel.
5. Remove dust. Vacuum thoroughly and wipe with a tack cloth.
6. Apply next coat. Brush or wipe on polyurethane smoothly, avoiding overworking.

Special Cases

If using water-based polyurethane, sanding may not be necessary between every coat. However, for oil-based polyurethane, sanding between all coats is strongly recommended.

Pro Tips

• Use a sanding block for flat surfaces—fingers alone create uneven pressure.
• Sand lightly—don’t cut through the finish, just smooth it.
• Vacuum dust before applying the next coat to avoid contamination.

Aftercare

• Allow final coat to cure for several days before heavy use.
• Buff with 0000 steel wool or polishing pads for an ultra-glossy finish.
• Clean with mild soap and water—avoid harsh chemicals.

FAQs

• Do I need to sand after the final coat? No—unless you want to buff for extra gloss.
• Can I use a power sander? It’s safer to sand by hand to avoid cutting through layers.
• What happens if I skip sanding? The next coat may peel or show defects more clearly.

Watch & Learn

Stock up on the right grits: From 320 to 600 grit, get packs in 25, 50, and 100 sizes for your finishing projects. Shop fine sandpaper.