Choose your grit progression: a science-backed sanding schedule
Sanding is not about removing material. It is about progressively removing the scratches left by the previous grit. The art of a professional sand is choosing a progression that each step fully removes the scratches from the step before, without leaving any of its own scratches deeper than the next step can remove.
The Australian Timber Flooring Association Code of Practice for Sanding and Coating of Timber Floors provides recommended grit progressions by species and coating system. Below is the EcoGrit distillation of that guidance, plus our own workshop observations from ten years on Australian hardwood.
The 2x rule
The industry rule of thumb: never skip more than one grit. In practice, each step should be approximately double the abrasive particle size of the previous step, i.e. half the grit number. 40 to 60 is fine. 40 to 80 is borderline. 40 to 120 is a guarantee of visible scratch marks in the finished floor.
Why? Because the scratch depth left by a belt is roughly proportional to particle size. A 40-grit belt leaves scratches ~120 microns deep. A 120-grit belt can only remove ~40 microns per pass. It cannot erase a 40-grit scratch in three passes, let alone one.
Recommended progressions
Three common systems, each with a different final step.
Hard wax oil finishes (Rubio, WOCA, Ciranova)
- 40 grit (or 36 if floor is previously painted or badly damaged)
- 60 grit
- 80 grit
- 100 grit
- 120 grit (final) - buff only, no belt
Never exceed 120 grit. Finer grits burnish the timber cells closed and reduce oil uptake by 40-60%, producing patchy colour and poor penetration.
Water-based polyurethane film finishes (Berger AquaSeal 2K PU)
- 40 grit
- 60 grit
- 80 grit
- 100 grit
- 120 grit (buff)
- Water pop if staining
- 120 grit re-buff
Optionally finish at 150 grit for very fine-textured timber (European Oak, Ash) but only if directly applying primer, never if water-popping.
Oil-based polyurethane
- 40 grit
- 60 grit
- 80 grit
- 100 grit (buff, final)
Oil-based polyurethane bonds better to a slightly coarser surface. Do not exceed 100 grit.
When to start coarser than 40
Start at 36 grit or 24 grit (on a drum, not a belt) when:
- Cupping > 1.5 mm (floor has absorbed excess moisture and bowled)
- Paint or varnish thicker than 200 microns
- Polyurethane in multiple layers from previous refinishing cycles
- Oil or food stains penetrated into the grain
From 36, progress: 36 -> 60 -> 80 -> 100 -> 120 (not 36 -> 40 -> 60, which is wasteful duplication).
Abrasive quality matters
Premium belts (sia, Mirka, 3M) use ceramic or zirconia alumina grits that fracture on impact to expose fresh cutting edges. Cheap belts use aluminium oxide that rounds over quickly, leaving the last half of a belt "polishing" rather than cutting.
A $35 premium belt that cuts cleanly for 300 m² leaves a measurably cleaner scratch pattern than a $15 belt that needed to be changed at 150 m². The saving is false economy and the final finish reads differently. EcoGrit stocks sia Abrasives as the EU trade benchmark; trade accounts receive volume-pricing.
Equipment alignment
Scratch pattern comes from three factors: grit, abrasive quality, and machine calibration. A drum that is not flat produces a wave pattern no finer grit can remove. A belt that is tensioned incorrectly chatters on interlocking grains.
ATFA-certified finishers calibrate drums and belts per every service cycle. At the DIY level, rental machines are serviced by the hire centre - if yours sounds rough, swap it. A bad machine ruins the floor.
Edger and corner work
The edger works in a different cut direction to the belt / drum. Scratch patterns overlap at the transition. Keep edger grit progression running one step behind the field:
- Field 40 -> edger 40
- Field 60 -> edger 50 or 60
- Field 80 -> edger 80
- Field 100 -> edger 80 or 100
- Field 120 -> edger 120 (or blend with the buffer)
Read more about avoiding the edge halo in our dedicated guide.
Common mistakes
- Skipping from 40 to 100. Sand scratches visible under finish. Go back and re-cut at 60 and 80.
- Stopping too early. Leaving the floor at 80 produces a texture that shows every dust mote under a gloss finish.
- Over-sanding on engineered. Most engineered flooring has a 3-4 mm wear layer. Full 40-grit progression can consume 1-1.5 mm. Start no coarser than 60 on engineered, and finish at 120.
- Wet sanding. Do not wet-sand timber floors. Water opens the grain unpredictably and the result is blotchy finish uptake.
Our trade advice
Run the 40-60-80-100-120 progression. Use quality ceramic belts. Buff the final grit with a 12-inch weighted buffer. Vacuum thoroughly at each grit change, not just at the end.
For abrasive recommendations by species or abrasive quantity estimates for your project size, call +61 401 270 818. We stock sia Abrasives for trade and retail, and we will estimate the right quantities for your sand.