How to Sand Drywall Joints Without Causing Flashing or Uneven Sheen

Even a perfectly taped drywall joint can look uneven once painted if the sanding isn’t handled correctly. Flashing—those visible dull or shiny patches under paint—happens when joint compound and paper face reflect light differently. The key is not just smoothing the joint, but feathering it into the surrounding surface with the right grit progression and light control. Here’s how to sand drywall joints for a flawless, invisible finish.

Why Sanding Technique Matters

Drywall compound is softer than the surrounding paper face. Over-sanding can cut through to paper, while under-sanding leaves visible ridges or tool marks. Controlled sanding removes excess mud and blends transitions evenly without damaging the paper or altering texture absorption before painting.

Recommended Tools

• Pole sander or hand sanding block with hook-and-loop pad
• 9x11" silicon carbide sandpaper sheets or mesh
• Dust mask or respirator
• Raking LED light or inspection flashlight
• Tack cloth and vacuum

Ideal Grit Sequence

• 120 grit: Knock down ridges and flatten compound
• 150 grit: Blend seams into surrounding drywall
• 220 grit: Final smoothing for paint or primer

Step-by-Step: Sanding Drywall Joints Smooth

1. Inspect under light. Position a raking light across the joint to reveal highs and lows. Mark any visible ridges or tool lines with a pencil.
2. Flatten ridges. Use 120 Grit (25-pack) sandpaper on a sanding block. Work in long, even strokes across the seam—not along it—to level out compound thickness.
3. Feather edges. Switch to 150 Grit (50-pack) and sand outward 6–12 inches on both sides of the joint. Keep strokes light and blend until the surface feels continuous under your palm.
4. Final finish. Finish with 220 Grit (100-pack) to remove fine scratches. Avoid sanding directly over screw heads—spot sand them gently to avoid exposing metal.
5. Clean and check. Vacuum the wall and shine the raking light again. Any visible line or halo means more feathering is needed before priming.

Special Cases

For wet or hot-mud joints, let compound cure fully before sanding to prevent clogging the abrasive. For existing painted walls, scuff-sand the entire area lightly with 220 grit to equalize sheen and improve paint adhesion.

Pro Tips

• Always sand in circular or crosshatch motions to avoid flat spots.
• Use mesh abrasives for less clogging on large jobs.
• Keep pressure light—sandpaper cuts faster than you expect on soft joint compound.
• Prime with a drywall sealer before painting to eliminate flashing and texture contrast.
• Replace paper as soon as it loads up; clogged grit polishes instead of cuts.

Aftercare

• After priming, inspect under angled light again—minor imperfections may reappear as shadows.
• Lightly re-sand with 320 grit between coats for ultra-smooth finishes.
• Wipe walls with a damp microfiber cloth before the final coat of paint to remove dust haze.

FAQs

• Should I wet sand drywall? Wet sanding reduces dust but dulls texture; use for small touch-ups, not large areas.
• Why does my paint look patchy? That’s flashing—apply drywall primer and ensure even sanding depth before painting.
• Do I need to sand between coats of mud? Yes—lightly scuff each layer to remove high edges before applying the next.

Watch & Learn

For consistent drywall results, use durable silicon carbide sandpaper from the fine sandpaper collection. Their sharp cut and clog-resistant backing keep surfaces smooth and ready for paint.

Conclusion: A flawless drywall finish begins with smart sanding. Follow the 120–150–220 grit sequence, keep your strokes even, and inspect under light—your joints will disappear under paint, leaving walls perfectly uniform.