For most drywall joint compound, start with 120- or 150-grit sandpaper, then finish with 220-grit for a paint-ready surface.
Why Grit Choice Shapes The Finish
USG’s finishing handbook notes that coarse abrasive scratches remain under primer and recommends 120-grit or finer for standard compound and 150-grit or finer for lightweight blends. 3M lists 150-grit sheets as the sweet spot for flattening seams without scarring the paper face. Family Handyman’s grit chart reminds users that higher numbers equal finer mineral size, which smooths instead of gouging. Careful selection, then, shields finished walls from surprise swirl marks.
| Stage | Recommended Grit | Primary Aim |
|---|---|---|
| Knock-down of heavy ridges | 100-120 | Flatten trowel lines and high spots. |
| General leveling pass | 150 | Blend compound into paper face. |
| Final feathering before primer | 180-220 | Erase swirl marks and leave a velvety profile. |
Choosing Sandpaper Grit For Drywall Mud
Home Depot suggests knocking down dried ridges with 100- or 120-grit, then shifting to 150-grit for broad seams. Fine Homebuilding backs the 150-grit norm for whole-wall passes and keeps finer sheets for touch-ups. Bob Vila places 120- to 150-grit in the same role and reserves 220-grit for the last skim that erases hairline scratches. This sequence removes tool marks without slicing through tape.
What The Numbers Mean
Grit numbers follow the CAMI scale. A 100-grit sheet carries roughly 150-micron particles, while 220-grit drops below 70 micron. Lower numbers slice; higher numbers polish. The modest jump between 120 and 150 keeps the scratch pattern even, letting the next grit work faster.
Compound Type Alters The Plan
Lightweight joint compounds sand easier yet scratch faster. USG advises skipping coarse sheets and beginning at 150 when using topping or lightweight mud. Heavy all-purpose mud can handle 120-grit on the first pass, though steady pressure and a flat pad keep the paper facing safe.
Patch Size Guides Grit Choice
Small patches dry harder than full coats, so a 120-grit sanding sponge often feels firm enough. Larger surfaces benefit from pole sanders with 150-grit screens because the mesh sheds dust and resists clogging.
Best Sandpaper Grits When Sanding Joint Compound
The five-step plan below blends advice from USG, tool makers, and pro finishers.
Step 1 – Locate High Spots
Rake a low-angle work light across the surface and mark ridges with a pencil. This reduces blind sanding and shortens time with coarse paper.
Step 2 – Knock Down Ridges
Use a 120-grit sheet or screen and a hand sander. Keep the pad flat and push from fresh compound toward the paper edge. Stop once the ridge blends.
Step 3 – Level The Field
Shift to 150-grit. Pole sanders cover wide seams without creating dips. 3M’s 150-grit drywall sheets and screens come pre-cut for pole handles so they stay flat over the joint.
Step 4 – Feather And Polish
Once the seam feels flush to a straightedge, wipe with a brush. Pass 180 or 220-grit lightly to erase swirl marks. HGTV notes that a light sweep with 220-grit brings patched areas flush with the surrounding wall finish.
Step 5 – Check Under Primer
Primer can lift nap and show hidden scratches. After the first coat dries, sand again with 220-grit as This Old House advises for trim and walls alike.
Hand, Pole, Or Sponge?
Fine Homebuilding prefers a hand sander for corners and a pole sander for seams, both loaded with 150-grit or finer. Screens cut faster on wide areas because dust drops through the mesh, while paper leaves a tighter scratch on detail work. A sanding sponge wraps around inside corners and helps avoid shredding tape.
Dust Control Boosts Visibility
Light grit means lighter scratches, yet dust still hangs in the air. 3M’s open mesh screens limit clogging and let drywall powder fall through holes. Better Homes & Gardens adds that stepping outdoors to clean sheets keeps dust away from fresh mud.
When To Switch Grit
Swap once the surface is flat but still dull. 150-grit leaves a haze that wipes off with a damp cloth. If ridges remain after two slow strokes, stay on the same grit; moving up too soon traps low spots.
| Symptom | Likely Cause | Solution |
|---|---|---|
| White scratches visible through primer | Grit too coarse or heavy pressure | Re-sand with 180-220, then prime again. |
| Paper face torn | Pad tilted or grit under 120 | Skim a thin coat, sand with 150. |
| “Pillowy” seams | Moved to fine grit too early | Return to 120-150 over the high edge only. |
Safety Gear For The Job
N95 masks capture airborne gypsum; goggles shield eyes; a headlamp highlights ridges during inspection.
Ceiling And High Wall Strategy
Ceilings hide fewer flaws because light grazes across them. Home Depot explains that a pole sander fitted with a 150-grit screen works best overhead, keeping elbows down and the pad flat. Move in slow arcs; brisk strokes lift one edge and create tramlines. Where two ceilings meet in a valley, switch to a fine-edge sanding sponge so the crisp angle stays sharp.
Wet Sanding Option
Some finishers prefer wet-sanding the final pass to keep dust down. Bob Vila lists a damp sponge as a way to erase small burrows after the second coat dries. Wring the sponge nearly dry, rub in one direction, rinse when clogged, and follow with 220-grit once the surface dries.
Reusing Screens And Sheets
Drywall screens fill slower than paper. A quick knock against a stud clears most dust. When the mineral dulls, flip to the fresh side; each screen cuts twice before disposal. 3M notes that its silicon-carbide mesh tolerates water rinse, restoring bite after heavy use.
Routine Checks Between Grits
Shine a flashlight across the wall after each grit. Any mark that catches the beam will show under paint. Stop and skim pits before moving on. Mark spots with a soft-lead pencil; This Old House warns that ink may bleed through latex paint.
Maintaining Even Pressure
Uneven push creates waves. Fine Homebuilding teaches that the wrist stays locked while the elbow guides the pole sander, letting the abrasive glide along rather than bounce.
Common Sanding Mistakes
Skipping grits: jumping from 120 to 220 looks quicker yet leaves witness lines.
Grinding corners: driving the pole head into inside angles shreds tape. Fold a 150-grit sheet by hand instead.
Over-sanding fasteners: the shiny cap of a screw polishes sooner than compound; stop once the halo disappears.
Sanding too soon: damp compound clogs paper and forms pills. Wait until the surface turns consistent white.
Primer And Grit Relationship
Paint makers label drywall primers “high build,” yet these coatings hide only shallow scratches. This Old House recommends scuff-sanding moldings and walls with 220-grit to help primers bond and to remove lint raised by earlier coats.
Ceiling Light Test Before Painting
Dim the work light and tilt a bare bulb near the surface. Shadows exaggerate leftover scratches. Carry a postage-stamp piece of 220-grit to buff stray nubs on the spot.
Screen Versus Paper: When Each Wins
Screens resist caking, suit pole sanding, and survive rinse. Paper makes a tighter scratch, costs less, and wraps over sponge blocks for spot work. Lowe’s lists 150-grit drywall sheets sized for common handles, letting users swap between paper and screen without changing tools.
Repairing Damage From Over-Sanding
If the brown paper layer shows, seal it, let it dry, skim a thin coat, and sand with 220-grit only after curing. Paint alone never hides the fiber texture.
Sanding On Rapid-Set Compound
Rapid-set powder cures harder than regular mud. Family Handyman suggests starting at 100-grit with these products, then progressing the usual way. Keep fresh sheets close; fast-dry powder carries quartz that dulls sandpaper in minutes.
Dust Collection Tips
Attach a vacuum hose to the pole head if available. Homebuilding & Renovating says dust control not only protects health, but also sharpens surface inspection during the job.
Field Checklist
- Start at 100-120 only on ridges, progressing once flat.
- Lock the wrist, guide with the elbow.
- Move the light often to cross-check scratches.
- Finish with 220 and wipe walls with a microfiber cloth.
- Prime, sand lightly with 220, then paint.
Wrap-Up
The smoothest drywall emerges from a short grit ladder: 120 to flatten, 150 to level, 180-220 to polish. More stages mean fewer scratches and less filler later. If unsure, consult USG’s drywall finishing handbook for a grit range matched to the compound in use.