What You'll Need
Gathering everything before you start saves trips up and down the ladder. Here's my standard sanding kit:
- Sanding pole with swivel head ($25 to $40)
- Hand sanding block with foam backing ($8 to $12)
- 120-grit sanding screens or paper
- 150-grit sanding screens or paper
- 220-grit sanding screens or paper
- N95 dust mask (minimum) or half-face respirator
- Safety glasses or goggles
- Shop vacuum with drywall filter ($15 to $30 for filter alone)
- Plastic sheeting and painter's tape
- Work light with adjustable angle
- Damp sponge for wet sanding option
Total cost for someone starting from scratch: about $100 to $150. The sanding pole and shop vac filter are the big expenses. Everything else is cheap.
Step 1: Set Up Dust Containment
Do this before you touch sandpaper. Drywall dust is incredibly fine. It gets into everything. HVAC ducts. Electronics. Carpet fibers. Once it's in, it's hard to get out.
Cover HVAC vents with plastic and tape. Close doors to other rooms. Hang plastic sheeting across doorways if the room doesn't have a door. Put down drop cloths on floors, especially carpet.
Brother-in-law Jeff skipped this step when he flipped that house. Sanded three rooms with no containment. The dust ended up in the ductwork. Every time the heat kicked on for the next month, white powder puffed out of the vents. He spent more on duct cleaning than he saved by rushing.
The Box Fan Trick
Put a box fan in a window, blowing out. Tape a furnace filter to the back of it. This creates negative pressure in the room, pulling dust toward the window instead of into the rest of your house.
Cheap setup. Maybe $30 if you don't already own a box fan. Works surprisingly well. Uncle Frank taught me this one.
Step 2: Start with 120-Grit
120-grit is aggressive. It takes material off fast. You're using it to knock down high spots and ridges, not to create a final finish.
Work the sanding pole in circular motions first to find the bumps. You'll feel them through the pole. Then switch to straight strokes along the length of the joint to smooth everything out.
Don't press hard. Let the grit do the work. Pressing hard creates gouges and swirl marks that you'll have to fill and re-sand.
When to Skip 120
If your finish coats are already smooth with just minor imperfections, start at 150. The goal is minimal sanding. Every pass removes material you worked hard to apply.
Step 3: Progress to 150-Grit
150-grit smooths out the scratches left by 120. Same technique. Light pressure. Long strokes along the joints.
This is where I spend most of my time. The transition from 120 to 150 makes the biggest visual difference. You're removing scratch patterns and starting to get that smooth, ready-for-paint surface.
Dave tends to stop here. He says 150 is good enough. Carlos disagrees strongly. "I can see 150 scratches through primer," he told me once. "Every single time." He's not wrong, but he's also painting professionally and has higher standards than weekend DIYers.
Step 4: Finish with 220-Grit
220-grit is your finish pass. It removes the fine scratches from 150 and leaves a surface that disappears under paint.
By this stage you're barely removing any material. Light pressure. You're polishing more than sanding. If you're creating dust clouds at 220, you're pressing too hard.
I use a hand sanding block for 220 work. The pole is great for coverage, but the block gives better control for final touch-ups. You can feel subtle imperfections through the foam backing.
The Raking Light Test
Set a work light at a sharp angle to the wall. The shadows reveal every imperfection. Scratches, ridges, depressions, and anything the topcoat missed.
Do this between each grit step and again at the end. What looks fine under normal lighting often looks terrible at a raking angle. Fix problems now, not after primer.
Wet Sanding for Dust Control
After that first living room disaster, I learned about wet sanding. It eliminates almost all airborne dust. Not completely dustless, but close.
You use a damp sponge instead of sandpaper. The sponge smooths the compound while the water traps the particles. No clouds. No snowstorm. Just damp white residue that wipes away.
How Wet Sanding Works
Dip the sponge in water and wring it out until just damp. Too wet and you'll dissolve the compound. Too dry and you're back to making dust.
Work in circles, rinsing the sponge frequently. The surface will look streaky at first. That's fine. Let it dry and hit it with a light 220-grit pass if needed.
Downsides of Wet Sanding
Slower than dry sanding. You can't remove as much material. If your mud job has significant ridges or high spots, you'll need dry sanding first.
I use dry sanding with 120 and 150 for shaping, then wet sanding for the final pass. Best of both worlds. Most of the dust gets generated by the coarse grits anyway.
Common Mistakes to Avoid
I've made all of these. Learn from my screwups.
Over-Sanding
This is the big one. Sand too much and you go through the compound into the tape. Once you've exposed paper tape, you have to re-coat and wait for it to dry.
The tape usually shows as a slightly different texture before you actually break through. Stop as soon as you see it. The goal is to sand the compound level with the tape, not below it.
Lightweight compound makes over-sanding easy. The stuff comes off so smoothly that you can blow right through it without realizing. Check often.
Sanding Before It's Dry
Wet compound gums up sandpaper and leaves streaks. If your paper is loading with paste instead of creating dust, stop. Let it dry another day.
The compound changes color as it dries. All of it should be uniform light gray before you sand. Any darker spots mean moisture still inside.
Skipping Grits
Going straight from 120 to 220 doesn't save time. The 220 can't remove the deep scratches from 120. You end up spending longer than if you'd just done the progression properly.
The grits work together. Each one removes the scratches from the previous one. Skip a step and you're fighting physics.
Not Wearing a Respirator
Drywall dust isn't immediately toxic, but breathing it day after day isn't great for your lungs. An N95 mask costs $2. A half-face respirator with P100 filters costs $30 and lasts years.
Wear one. Every time. I didn't for my first few projects and I could taste grit for days afterward. Not worth it.
What to Expect After Sanding
A properly sanded wall feels smooth when you run your hand across it. No ridges. No scratches you can feel. The joint should be invisible, or close to it.
After sanding, wipe down with a damp cloth or tack cloth to remove dust. Then prime. Primer reveals every imperfection you missed. That's normal. Touch up with spackle, sand lightly with 220, and prime again.
Carlos says he goes through this cycle two or three times on high-end jobs. Even professionals don't get it perfect in one pass. Knowing that made me feel a lot better about my own learning curve.