Between-Coat Sanding for Poly: De-Nib & Level (320–600)

Ever laid down a beautiful coat of polyurethane only to find little dust bumps, tiny fibers, or a hint of orange peel once it dries? That’s normal. The fix isn’t heavy sanding—it’s a smart, gentle between-coat routine that knocks down nibs, levels minor texture, and sets you up for a glassy final coat. In this guide you’ll get a complete workflow, including which grits to use, how much pressure to apply, and how to inspect your surface so you never sand through or dull edges prematurely.

Why Between-Coat Sanding Matters

Polyurethane—especially waterborne—dries fast and traps whatever lands on it in the first hour: dust, fibers, even micro-bubbles. Those nibs telegraph through subsequent coats. A controlled de-nib/level pass creates a uniform, micro-toothed surface that new finish can bite into, while also removing tiny high spots so the next coat lays down flatter. Done right, you’ll use less finish overall and get a clearer, smoother build with fewer coats.

Tools You’ll Need

• Silicon carbide wet/dry sheets (9×11 in), grits 320–600. All eQualle sheets support wet or dry use.
• Soft sanding block or foam interface pad for flats; hand pad for profiles/edges.
• Raking light (LED bar or headlamp) to reveal nibs and subtle texture.
• Vacuum with brush, microfiber cloth, and a fresh tack cloth.
• Clean, lint-free wipe and mineral spirits or water (match your finish family) for surface checks.
• Nitrile gloves and a fresh, dust-free applicator for the next coat (foam or synthetic bristle, or an HVLP rig).

Recommended Grit Sequence

• 320 grit: Light de-nib; removes dust pimples without cutting through.
• 400 grit: Gentle leveling pass when you see faint orange peel or minor brush marks.
• 600 grit: Optional pre-final pass for ultra-clear topcoat flow and a silky touch.

Tip: Work dry for speed and feel. If paper loads or the air is dusty, a light mist (damp-sanding) keeps the sheet cutting clean and reduces airborne dust. Keep water away from oil-based films until fully cured.

Step-by-Step: De-Nib and Level Without Sand-Throughs

1. Confirm cure window. Follow the can: most waterborne polys sand in 1–2 hours; oil-based often needs 8–24 hours. If dust piles on your paper or the film smears, it’s not ready. Wait.
2. Stage your inspection light. Kill the overhead glare and sweep an LED at a low angle. Every nib casts a tiny shadow; light texture appears as a faint pebbled highlight. Mentally mark trouble zones before you touch paper.
3. De-nib with 320. Wrap a fresh sheet around a soft block. Use whisper-light pressure and long with-grain strokes. Aim to kiss the tops of bumps, not remove film. A dependable starting point is 320 Grit (25-pack)—fine enough to be safe, yet still effective on nibs. After two or three passes, re-inspect in raking light; nibs should flatten into the surrounding sheen.
4. Vacuum and tack. Vacuum thoroughly, then wipe with a microfiber. A very light tack keeps dust out of your next step. Dust left behind becomes tomorrow’s nib.
5. Level texture at 400 (as needed). If you see faint orange peel or brush ridges, glide 400 grit with minimal pressure. Focus on the affected region and then feather out three long strokes beyond it to avoid a witness line. For consistent results across cabinet runs or tabletops, keep bulk on hand like 400 Grit (50-pack).
6. Edge and profile caution. Switch to a hand pad or folded sheet on edges, molding, and bevels. Let the pad conform; if the raking highlight suddenly widens on an edge, you’re thinning the film—back off and use feather-light touch only.
7. Fix localized flaws smartly. Tiny runs/sags? Shave cured drips with a razor held nearly flat, then level at 400. Pinholes from bubbles? Perforate with a fine needle, spot-sand at 400, and plan a slightly wetter next coat.
8. Optional refinement at 600 before the last coat. For gloss or high-clarity waterborne poly, a quick 600-grit pass can make the final coat melt in beautifully. Keep the pressure feather-light—this is refinement, not removal. For shop-wide consistency, stock a contractor box like 600 Grit (100-pack).
9. Clean to perfection. Vacuum again. Wipe with a compatible solvent (water for waterborne; mineral spirits for oil) to preview clarity and find any remaining scratches. If you see a uniform matte, you’ve created ideal tooth for the next coat.
10. Recoat technique. Stir, don’t shake. Strain into a clean tray or cup. Apply a thin, even coat with consistent overlap. Maintain a wet edge and work under good light so you can see your film.

Special Cases & Adjustments

Waterborne poly: Tends to raise grain on early coats; the 320 pass doubles as a whisker knock-down. It also dries fast—work in smaller sections so you don’t outrun your wet edge.

Oil-based poly: Sands like butter once cured, but waits are longer. Err on the side of patience; half-cured oil will clog paper and smear.

High-build on tabletops: If you’re stacking multiple coats for a poured-glass look, keep each between-coat pass minimal. Heavy leveling should happen once you’re within one coat of final thickness.

Dark colors and high gloss: They reveal everything. Use a meticulous 320 → 400 → 600 progression and clean between each step. Inspect under cross-lighting from two angles.

Dusty shop days: Dampen the floor, wear a clean shirt, and turn off forced-air blowers while the film flashes. Cover nearby tools that shed dust (sanders, vacs) with a clean cloth.

Pro Tips

• Pressure discipline: The lighter you sand, the flatter your next coat will look. Let the grit do the work.
• Fresh paper, fast wins: Silicon carbide cuts sharp but loads as films warm. Swap sheets early to keep scratches consistent.
• Raking light is your superpower: Sweep it north-south and east-west. If a defect survives one direction, you’ll catch it in the other.
• Block for flats, pad for curves: Blocks keep tabletops dead-flat; pads conform to raised panels and molded rails.
• Thin the final coat (optional): A slight reduction (per manufacturer) helps self-level on large fields.
• Wet last, if you do: A light damp-sand at 600 (waterborne only) can leave an ultra-even scratch field for your final coat.

Aftercare

• Hands off during cure: Even when it’s dry to touch, full cure can take days. Avoid heavy items and hot cups on tabletops.
• Final rub-out (after full cure): For mirror gloss, you can level with 1000–2000 grit and polish; for satin, stop at 1000 and burnish lightly. Always confirm the finish is fully cured first.
• Clean gently: Mild soap and water on waterborne; damp cloth on oil-based for the first week. Skip harsh cleaners.
• Protect edges: They wear first. Use coasters and felt pads under décor to prevent micro-scratches.

FAQs

• Do I have to sand between every coat? If the recoat window allows chemical adhesion, you can sometimes skip sanding—but de-nibbing yields a flatter, cleaner result. Most pros do a quick pass every time.
• Why 320, 400, and 600? 320 safely knocks nibs; 400 refines texture; 600 preps for a glassy final coat without over-polishing.
• Will sanding make the finish cloudy? A uniform matte is good; gloss returns when you recoat. Cloudiness only persists if you trap dust or leave uneven scratches—use raking light to confirm uniformity.
• Wet or dry? Dry for feel and speed; a light damp pass reduces dust for waterborne films. Avoid water on oil-based until cured.
• What about between-coat tack cloth? Use a fresh tack lightly, or a microfiber plus a solvent-compatible wipe. Heavy pressure can leave residue.

Watch: Between-Coat De-Nib Basics

Closing

Between-coat sanding isn’t about grinding off finish—it’s about tuning the surface so your next layer floats on flat and dries clean. Keep it light, keep it clean, and follow a simple progression: de-nib with 320 Grit (25-pack), level at 400 Grit (50-pack) when needed, and, for showpiece clarity, refine with 600 Grit (100-pack) before the final coat. The payoff is a clearer, flatter finish in fewer coats—and a project you’re proud to show off.