Floor Sanding Abrasive Grit Guide: Which Grit for Each Stage?

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Selecting the right sanding abrasive grit sequence is critical to achieving a smooth, professional timber floor finish. Use the wrong grit at the wrong stage and you create scratches that show through your oil or lacquer. This guide explains each grit level, when to use it, and which abrasive types work best for Australian hardwoods and softwoods.

How Grit Numbers Work

Grit numbers refer to the size of the abrasive particles on the disc, belt or paper. Lower numbers mean coarser, more aggressive cutting. Higher numbers mean finer, smoother finishing. A 24-grit disc removes material fast. A 150-grit disc creates a smooth surface ready for coating.

The standard sanding sequence moves from coarse to fine in controlled steps. Skipping grits or jumping too far between stages leaves visible scratch patterns in the finished floor.

Grit Progression: Never Skip More Than One Grit

After the first cut, sanding is about removing the scratches left by the previous grit. A good grit progression lets each step fully remove the scratches from the step before, without leaving scratches of its own deeper than the next step can remove.

The rule from sanding machine and abrasive makers such as Lägler and Pallmann is simple: never skip more than one grit. Lägler's common grit sequence runs 16, 24, 30, 36, 40, 50, 60, 80, 100, 120, 150. Going from 40 to 60 skips one grit, which is fine, and so does 60 to 100. Going from 36 to 60 skips two (40 and 50) and breaks the rule. Scratch depth follows particle size, so a fine grit cannot erase a much coarser scratch in any sensible number of passes.

The right progression depends on the finish going down:

Hard wax oil and oil finishes (Rubio Monocoat, WOCA): 40, 60, 80, then finish at 100 or 120. Go no finer than 120. Finer grits burnish the grain closed and cut oil uptake, which shows up as patchy colour.

Water-based polyurethane (such as Berger-Seidle AquaSeal): 40, 60, 80, 100, 120. If you are staining, water pop after the final grit, as the last step before the stain. Our water popping guide explains when it helps.

Oil-based polyurethane: 40, 60, 80, 100. Go on to 120 only if the coating's data sheet calls for it.

When to start coarser than 40: start at 40 on most floors, and go coarser only when the floor is badly damaged or heavily coated, for example cupped or uneven boards, thick paint or varnish, several layers of polyurethane from past refinishing, or stains soaked deep into the grain. Lägler advises starting with as fine a grit as the floor allows, because a finer first cut takes less time and wastes less timber. From a coarse start the one-grit rule still applies: 24, 36, 50, 80 works, and so does 36, 40, 60, 80. Then carry on to your finish's final grit.

Engineered boards: an engineered board has a limited hardwood wear layer over its core, and a coarse first cut can go straight through a thin one. Start at 60, and drop to 40 only if 60 will not lift the old coating. If you are unsure how thick the wear layer is, check with the flooring manufacturer before you sand.

Edger: the edger runs the same grit as the drum at each stage. 40 on the floor means 40 on the edger, 60 means 60, and so on. The edges start at 40 on most floors, go coarser only on badly damaged or heavily coated floors, and finish at the same final grit as the field. If the edges finish at a different grit, the perimeter reads as a frame under the coating. That is the edge halo effect.

Coarse Grits: 16 to 40

Use coarse grits for the initial cut. This stage removes old coatings, levels uneven boards and takes the floor down to fresh timber. Start with a 40-grit ceramic or zirconia belt on the drum sander. Only go coarser, to 36 or 24, on badly damaged or heavily coated floors, and then use one of the coarse-start sequences above.

Ceramic abrasives from SIA cut faster and last longer than standard aluminium oxide at this stage. They handle the heat generated during heavy material removal without glazing over.

Run the sander with the grain. Diagonal passes are acceptable on the first cut to level cupped boards, but follow up with a pass along the grain direction.

Medium Grits: 60 to 80

The medium grit stage removes the scratch pattern left by the coarse grit. A 60-grit pass followed by an 80-grit pass is the standard approach. This is where the floor starts to look smooth.

Zirconia abrasives perform well at this stage. They maintain their cutting edge longer than aluminium oxide and produce consistent results across the floor.

Pay attention to the edger work. Match the grit sequence on the edger to the drum sander. If you finish the main floor at 80 grit, the edges need to match before moving to fine grits.

Fine Grits: 100 to 150

Fine grits prepare the timber for coating. A 100-grit or 120-grit pass removes the medium grit scratch pattern and creates a surface smooth enough for oil or lacquer application.

For water-based lacquer systems like Berger-Seidle AquaSeal, finish at 120 grit. Water-based products highlight fine scratches, so the surface needs to be clean and consistent.

For oil finishes like Rubio Monocoat or WOCA, 100 to 120 grit works well. Going too fine with oil finishes reduces absorption. The timber needs some tooth for the oil to grip.

Abrasive Types Explained

Aluminium Oxide: The most common abrasive. Good all-round performance. Cost-effective for fine grit work and general sanding.

Zirconia: Harder than aluminium oxide. Self-sharpening as it wears. Ideal for medium grits and hardwood species like spotted gum, blackbutt and jarrah.

Ceramic: The hardest and longest-lasting option. Best for coarse grit work and heavy material removal. SIA ceramic discs and belts are the professional standard in Australia.

Disc, Belt or Paper?

Drum sanders use belts for the main floor area. Edgers use discs. Orbital or multi-disc machines use paper or mesh pads for the final screening pass.

Match the abrasive type to the machine and the stage. Ceramic belts on the drum for the first cut. Zirconia discs on the edger for medium work. Aluminium oxide mesh on the buffer for the final screen.

Common Sanding Mistakes

Skipping grits. Jumping from 36 straight to 100 leaves deep scratches that the fine grit cannot remove. Follow a progression that never skips more than one grit, such as 40, 60, 80, 100, 120. If you have jumped more than one grit, go back and add the missing steps so that no step skips more than one grit.

Using worn abrasives too long. A dull disc generates heat, burns the timber and creates an uneven surface. Change abrasives when they stop cutting efficiently.

Ignoring the edges. The edger needs the same grit progression as the drum sander. Mismatched edges show clearly once the finish is applied.

Recommended Grit Sequence

For most Australian hardwood floors, this sequence delivers professional results:

First pass: 40 grit (ceramic belt on drum sander)
Second pass: 60 grit (zirconia belt on drum sander)
Third pass: 80 grit (zirconia or aluminium oxide)
Fourth pass: 100 or 120 grit (aluminium oxide)
Final screen: 120 or 150 grit (mesh pad on buffer)

For hard wax oil and oil finishes, screen no finer than 120. If a badly damaged or heavily coated floor needs a coarser first cut, use one of the coarse-start sequences in the grit progression section above.

EcoGrit stocks a selection of SIA professional sanding abrasives, including zirconia floor sanding belts and sanding discs. Browse the Abrasives collection to find what you need for your next job.

See also: timber floor sealers.

See also: professional lacquer systems.

See also: timber floor finishes guide.

See also: common lacquer application mistakes.

Sources

• Lägler, Sanding of wooden floors, floor sanding manual (PDF)
• Pallmann, Pallmann Spider Sanding Recommendations, info sheet (PDF)

Products in this guide

• sia abrasives range - professional sanding belts and discs
• sia 2800 zirconia sanding belt 200x750mm - for 8-inch drum floor sanders
• sia 1749 sanding disc 178mm CH-Star - for floor edge sanding
• sia 1815 sanding disc 150mm siafast - for timber floor sanding with 150mm discs

All available from EcoGrit, shipped Australia-wide. Trade pricing available for flooring professionals.