How to Choose and Use a Random Orbital Sander
I’ve been sanding floors, decks, doors and dining tables for long enough to tell you the truth nobody at the tool counter wants to admit: the brand of random orbital sander on your bench matters far less than the grit ladder you climb with it. I’ve watched blokes spend $600 on a Festool ETS EC 150 and still leave swirl marks on a spotted gum coffee table because they jumped from 80-grit straight to 180. I’ve watched a $79 Ozito do beautiful work on a jarrah door because the owner went 80, then 120, then 180, and changed paper before it glazed. My apprentice Jacob argued with me about this on his second week on the tools — he wanted to “save time” by skipping 120 on a refinish job. We sanded that table top three times before the swirl marks finally came out. Cheap lesson. So this guide is about technique first, machine second. The grit ladder is what separates a finish that looks like glass from one that catches the afternoon light and shows every circle.
What you’ll need
- A random orbital sander — 125 mm pad is the sweet spot for furniture and doors, 150 mm if you’re tackling decks or large table tops
- Open-coat aluminium oxide discs in 80, 120 and 180 grit (Festool Granat or Mirka Abranet — not the cheap general-purpose multipack)
- A vacuum extraction hose, or at minimum the dust bag fitted and emptied every five minutes
- A P2 dust mask (P3 if you’re sanding old paint that might be lead-based — anything pre-1970)
- Safety glasses and earmuffs (a 5 mm orbital running for an hour will damage hearing)
- A tack cloth or microfibre and metho for between-grit clean-down
- A pencil — yes, a pencil. I’ll explain
- A clean rag and a soft brush for the disc face mid-job
Step 1: Pick the right sander for the job, not the biggest one
For 90% of household jobs — doors, table tops, chairs, skirting prep — a 125 mm 5 mm-orbit machine is what you want. The Bosch GEX 18V-125 (cordless) and the corded Makita BO5041 are both excellent. If you’re doing deck boards or large flat panels, step up to a 150 mm 6 mm-orbit machine like the Festool ETS 125 with the right pad, or the Bosch GEX 150 AC. A bigger orbit removes more material faster, but it also leaves deeper scratches you have to chase out — which is why deck-flatting machines have 6 mm orbits but fine-furniture sanders have 2–3 mm. Match the orbit to the work, not the wallet.
Step 2: Buy open-coat paper, not the Bunnings four-pack
This is the single most important sentence in this article. The “general purpose” sandpaper packs at the front of the abrasives aisle are closed-coat — grit packed tightly across the disc face. They work fine on pine and MDF. On Aussie hardwoods they glaze inside thirty seconds because there’s no space for the resinous dust to clear. You want open-coat aluminium oxide or ceramic discs. Two names that matter: Festool Granat (yellow) and Mirka Abranet (mesh, looks like a tea-strainer). Both clear dust, both last 5–10 times longer on hardwood, both cost roughly twice as much per disc — which is a third of the cost per square metre sanded. Bunnings stocks Mirka in the trade aisle. If yours doesn’t, order from Sandpaperman or Timbecon online.
Step 3: Hook up dust extraction or accept the consequences
A random orbital sander without dust extraction is a machine for sanding the same square of wood ten times because the dust keeps re-cutting your surface. Plug into a shop vac with the right adapter (most sanders ship with a 27 mm or 35 mm port) and your discs last twice as long, your finish is twice as good, and your lungs thank you. The Festool CT MIDI vac is the gold-standard pairing, but a $99 Ozito wet/dry with the right cuff does 80% of the job. If you’re sanding deck timber that’s been oiled previously, the dust is also a fire risk — pile it on concrete in the sun, not in a bin.
Step 4: The 80→120→180 ladder — never skip a rung
The rule I’ve been preaching since 2009 and it has never failed me. Start at 80 grit to remove the old finish or flatten the surface. Go to 120 grit to remove the scratches the 80 left behind. Go to 180 grit to remove the scratches the 120 left behind. That’s it. Do not jump 80 to 180 — the 180 paper cannot remove an 80-grit scratch in any sensible timeframe; you’ll just polish around it and the swirl will show under finish. Do not start at 120 because the surface “looks okay” — if the old finish needs removing, you need 80. The ladder is non-negotiable. The number of swirl-mark callbacks I’ve taken over the years all traced back to skipping a rung.
Step 5: Use the pencil trick between grits
Before you start each grit, scribble pencil lines diagonally across the surface — light squiggles every 100 mm or so. Sand at that grit until every pencil line is gone. That tells you, objectively, that the grit has done its job and removed the previous grit’s scratches. If you skip this and just “sand for a bit”, you’ll move up to the next grit while 80-grit scratches are still hiding under glare. The pencil never lies and it costs nothing.
Step 6: Aussie hardwood gotcha — change paper before it glazes
On jarrah, spotted gum, blackbutt or merbau you’ll get 30–60 seconds out of an 80-grit disc before it starts to glaze. You’ll see it: surface goes shiny and grey instead of matte and tan, and the sander stops cutting and starts skating. Stop. Pull the disc off (Granat and Abranet are hook-and-loop, two seconds) and put a fresh one on. A glazed disc burnishes the timber, generates heat, and burns case-hardening into the surface that bleeds through stain and finish. On a 4 m deck plank in spotted gum you may go through four 80-grit discs. That’s normal. Buying open-coat paper is what makes this affordable. For deck work where you actually shouldn’t be using a sander at all, see how to strip and re-stain a timber deck — chemical strip beats sanding every time on a real deck.
Step 7: Sander technique — slow, overlapping, no pressure
Move the sander at about 25 mm per second. That’s slow — slower than feels right. Random orbital sanders cut by random orbit, not by you forcing them. If you push down, you stall the orbit, the pad bogs, and you leave swirl marks. Let the weight of the machine do the work. Overlap each pass by 50%. Keep the sander flat — never tilt onto an edge to “knock down a high spot”, that’s what a hand block is for.
Step 8: Sand with the grain on the final grit, only
Random orbital sanders sand in random direction by definition. That’s their gift. But on the final 180-grit pass on visible furniture surfaces, do a final pass moving the sander only along the grain direction. It removes the last cross-grain micro-scratches and the difference under stain is visible. On floors and decks where you’re going to coat with poly or oil, this matters less — but for a dining table it’s the difference between “decent DIY” and “looks bought”.
Step 9: Vacuum and tack between grits, always
Between 80 and 120, vacuum the surface, then wipe with a microfibre dampened in metho (methylated spirits). Same between 120 and 180. Why? Because a single 80-grit particle left on the surface will gouge a 180-grit-shaped channel into your finish. Five minutes of cleaning saves an hour of chasing scratches. This step is the boring one that nobody talks about and everybody skips, then they wonder why the table top has a long scratch they can’t explain.
Step 10: Stop at 180 for stain, 240 for clear oil, never higher
For most jobs — stain-and-poly tables, painted doors, varnished floors — 180 is the finishing grit. Going to 240 closes the wood pores so much that stain won’t penetrate evenly and you get blotchy uptake. For a clear-oil finish on fine furniture, 240 is fine. Above that you’re polishing, not sanding. See how to lay vinyl plank flooring for the substrate-prep rules once you put the sander away.
When to call a tradie
Random-orbital sanding furniture, doors and small floor patches is firmly a homeowner job. Call a tradie for full timber floor sanding (drum sander or trio, multi-day job, dust control needs are different); for pre-1970 paint that might contain lead (P3 mask and disposal protocols apply, not weekend territory); or for any wet-area substrate prep below tile — anything that breaks the waterproof membrane on a real bathroom or laundry is licensed work under AS 3740. Don’t sand down to or through a membrane chasing a level finish; locate the issue and call a waterproofer.
Common screw-ups
- Skipping the 120-grit rung — 80-scratches show through every finish coat, swirl marks for life.
- Using closed-coat general-purpose paper on Aussie hardwood — glazes in seconds, wastes paper, burns the timber.
- Pushing down on the sander to “make it cut faster” — stalls the orbit, leaves swirl marks.
- Not vacuuming between grits — a single coarse particle gouges the surface on the next grit pass.
- Going past 180-grit before staining — pores close, stain blotches, finish looks patchy.
Cost & time
Mid-range 125 mm random orbital: $150–$300 (Bosch, Makita, Ryobi). Pro Festool ETS 125: $550. Ozito casual: $79. Open-coat discs: $25 for a 10-pack at trade prices, expect to use 4–8 per job on hardwood. P2 mask and safety gear: $30 starter kit. Time on a dining table refinish: a Saturday morning with proper grit progression; double that if you cut corners. A tradie refinish on a 1500 mm dining table: $400–$700 depending on timber and existing finish.
The sander doesn’t matter. The grit ladder does. 80, 120, 180, with open-coat paper, pencil-line check between each, vacuum-extracted, and changed before it glazes. Do that with an Ozito and you’ll out-finish a Festool used wrong. I’ve refinished four jarrah dining tables and a 12 m spotted-gum deck this year and the only thing that’s changed in twenty years on the tools is the price of paper. Every other rule still holds. Do it once, do it properly, and the surface will outlast the next renovation.
