How to Sand Drywall Patch to Reduce Lap Lines

Jesse Rowan
2026-02-23T14:25:38-06:00

If your drywall patch are leaving visible ridges, the fix is usually a flatter sanding pattern and a better grit progression. Below is a simple workflow to reduce lap lines while keeping the wall smooth, even, and ready for primer. These Silicon Carbide sheets are suitable for wet or dry use, so you can choose the approach that fits your dust control setup.

Why Sanding Matters

Drywall compound is soft compared with the paper face. If you focus pressure on the seam line, you can remove mud unevenly and create troughs that show up under paint. The goal is to flatten the repair, then refine the scratch pattern so primer lays down evenly and doesn’t highlight sanding marks.

Tools

Sanding pole (for ceilings and tall walls)

Hand sanding block (for corners and tight spots)

Drywall sanding sponge (optional for feathering edges)

Dust mask or respirator and safety glasses

Work light (raking light) to reveal ridges and lap lines

Vacuum with brush attachment or microfiber cloth

Tack cloth or slightly damp rag (for final wipe)

Recommended Grit Sequence

150 grit (knock down ridges/high spots)

220 grit (blend and feather edges)

320 grit (refine scratch pattern before primer)

400 grit (final touch for a paint-ready surface)

Step-by-Step

1. Let the mud fully cure. Sanding too early is the fastest way to create tear-outs and shiny low spots. If it feels cool or rubbery, give it more time.

2. Find the ridges with raking light. Hold a work light or flashlight low across the surface so every hump and lap line shows up. Mark the high spots lightly with a pencil.

3. Start with 150 Grit (100 Pack) to knock down highs. Use light pressure and long strokes across the seam (not just along it). Your goal is to flatten ridges without digging into the paper face.

4. Switch to 220 Grit (25 Pack) to feather the edges. Widen your sanding area 6–12 inches past the repair so the transition disappears. Keep the block/pole flat to avoid grooves.

5. Finish with 320 Grit (100 Pack) for a uniform surface. This step removes the coarser scratch pattern so primer doesn’t “telegraph” sanding marks. One or two quick passes is usually enough.

6. Check your work again under raking light. If you still see a ridge, spot-sand only the high area, then blend back out with the finer grit.

7. Clean the dust completely. Vacuum first, then wipe with a microfiber cloth. For final prep, a slightly damp rag helps pick up fine dust—let it dry before priming.

8. Prime before paint. Primer evens porosity between paper and compound so your finish coat looks consistent. After primer dries, a light 320–400 grit scuff is optional if you feel any roughness.

Special Cases

Corner beads: Use a sanding block and keep it aligned with the bead edge so you don’t round it over. Work from the compound toward the metal/vinyl edge, not directly on it.

Ceilings: A pole sander helps keep pressure even. Take frequent light-checks so you don’t over-sand one side of the repair.

Skim coats: If you’re leveling high spots across a wider area, keep your strokes broad and overlap passes so the surface stays flat.

Pro Tips

Use the lightest pressure that still cuts—pressure creates divots.

Sand in a cross-hatch pattern (left-right, then up-down) to keep seams flat.

If you hit paper fuzz, stop and seal it with primer; don’t keep sanding the face paper.

For less airborne dust, you can lightly mist the surface and sand gently—then dry fully before priming (keep moisture minimal on drywall).

Feather wide: the wider the blend, the less visible the repair after paint.

Aftercare

Run your hand lightly over the repair after dust is removed; your fingertips catch defects your eyes miss.

Prime repaired areas before painting to prevent flashing.

If you spot tiny pinholes after primer, fill with a thin skim, let dry, and sand lightly with 320–400.

Keep leftover sheets flat and dry so they don’t curl before the next repair.

FAQs

Why do ridges show up after painting? Paint highlights changes in texture and sheen. A ridge that’s barely visible on raw mud can look obvious once it’s coated.

Do I have to use all the grits? For many small repairs, 150 → 220 → 320 is enough. Add 400 if you want an extra-smooth final pass before primer or between coats.

Wet or dry sanding for drywall? Dry sanding is typical. If you dampen to reduce dust, keep moisture minimal and let the wall dry completely before priming.

How do I avoid lap lines on patches? Feather compound wider, then sand beyond the patch edges with light pressure—don’t stop your strokes at the patch boundary.

Watch & Learn

Tip: pause the video after each grit change and run a quick raking-light check. That “inspect before you move on” habit prevents over-sanding and keeps seams invisible after paint.

Done right, drywall sanding is more about sequence and pressure than brute force. Keep your passes wide, your pressure light, and your grit changes purposeful, and the repair will blend into the surrounding wall.