Quick answer: Sand a hardwood floor with a drum sander in three passes – 36 or 40 grit to strip the old finish and flatten, 60 grit to remove the coarse scratches, 100 grit to smooth – working with the grain, overlapping each pass by half a belt width, and never stopping with the drum down. Edge with a matching grit after each pass, vacuum, then stain and seal. Between sealer coats, screen or hand-sand lightly with 320. The belt sizes rental drum sanders take are 8" x 19" (EZ-8), 7-7/8" x 29-1/2", 9-7/8" x 29-1/2", 11-7/8" x 29-1/2" and 11-7/8" x 31-1/2".
Before you start
- Clear the room, remove the base shoe or quarter-round, and set every nail head below the surface – one proud nail tears a belt.
- Seal doorways and vents; drum sanding makes a lot of fine dust.
- Check the floor thickness. Solid hardwood can be sanded several times; engineered floors have a thin wear layer and may take only one light pass.
- Rent the drum sander and an edger together, and get extra belts – a heavily finished floor eats 36 grit.
The grit sequence
| Pass | Grit | Purpose |
|---|---|---|
| 1 | 36 or 40 | Strip old finish, level boards, remove deep scratches and cupping. Use 24 only on very rough or heavily coated floors. |
| 2 | 60 | Remove the 36/40 scratches and even the surface. |
| 3 | 80 or 100 | Smooth for stain and sealer. 100 is the usual final grit; go to 120 on maple or for a water-based finish. |
| After sealer | 320 (or a 120–150 screen) | Light hand or buffer sanding between coats to knock down raised grain and dust nibs. |
The species and condition of the floor change the starting grit – oak with one old coat of poly may start at 40; a painted or multi-layer floor starts at 24 or 36 – but the principle holds: never skip more than one grit, or the coarse scratches show through the stain.
How to run the drum sander
- Load the belt per the machine, abrasive out, and tension it. Check the arrow if it's a lap-spliced belt.
- Start at one wall, about two-thirds of the way across the room, with the drum raised. Start the motor, begin walking forward at a steady pace, and lower the drum smoothly onto the floor.
- Sand with the grain – along the boards, never across (except a first diagonal pass on a badly cupped floor).
- Keep moving. The drum is always moving when it's down. Stopping for even a second digs a dip you can't fix.
- Lift at the end of the run before you stop, back up in the same track with the drum down (most machines cut in both directions), lift, and shift over.
- Overlap each pass by about half the belt width.
- Do the other third by turning around and sanding the remaining strip, overlapping into the finished area.
- Edge the perimeter and closets with the edger at the same grit, then scrape corners the edger can't reach.
- Vacuum thoroughly, change to the next grit, and repeat.
After sanding
Vacuum, then wipe with a damp (not wet) cloth or tack cloth. Apply stain if you're using one, let it dry fully, and apply the first coat of sealer. When it's dry, sand lightly with 320 by hand or run a buffer with a fine screen to level dust nibs and raised grain, vacuum, tack, and apply the final coat – or two.
Watch: sanding a floor with a drum sander
Floor sanding belt sizes
| Belt size | Fits |
|---|---|
| 8" x 19" | Clarke EZ-8 and similar 8" drum sanders |
| 7-7/8" x 29-1/2" | 8" belt-type floor sanders |
| 9-7/8" x 29-1/2" | 10" floor sanders |
| 11-7/8" x 29-1/2" | 12" floor sanders |
| 11-7/8" x 31-1/2" | 12" floor sanders (long belt) |
All are sold in 10-packs in 24 to 120 grit. Not sure which your rental machine takes? Measure the old belt – see how to measure a sanding belt – or check the model number against the list. Browse all floor sanding belts.
Mistakes to avoid
- Stopping with the drum down – dips.
- Sanding across the grain on the final passes – scratches that show under stain.
- Skipping grits – coarse scratches under the finish.
- Not vacuuming between grits – stray coarse grit under the fine belt.
- Running a loaded belt – burn marks. Change it.
- Forgetting the edger – a different scratch pattern at the walls, or a visible ridge.
