Aluminium oxide, silicon carbide or ceramic — which sandpaper do I need?
The grain, the backing and the coating are three separate choices on every pack. What each one changes, and the combinations that suit timber, metal, plaster and finishes.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 4 min
Short answer
Aluminium oxide is the general-purpose grain for timber, paint and metal, and it is what most sanding sheets and discs are. Silicon carbide is harder and sharper but more brittle, which suits finishing, wet sanding, plaster and glass. Ceramic is the toughest and cuts fastest under pressure, which is why it belongs on belts and coarse discs for heavy stock removal.
The abrasive aisle labels everything by grit number and almost nothing by what it is made of, which is why people buy the wrong paper and blame their technique. Three things vary independently: what the grain is, what it is stuck to, and how densely it is spread across the surface.
Step by step
- Choose aluminium oxide as the default.Tough, moderately hard, and it fractures as it wears to expose fresh cutting points. It is the brown or reddish paper on most sheets, discs and rolls, and it handles timber, painted surfaces, filler and most metals. If you buy one thing, buy this.
- Choose silicon carbide for finishing and wet work.The dark grey or black paper. Harder and sharper than aluminium oxide but more brittle, so it cuts beautifully at fine grits and breaks down faster under heavy pressure. It is the grain in wet-and-dry paper, and the right choice for rubbing down between coats, cutting back a finish, sanding plaster and filler, and working on glass, stone and non-ferrous metal.
- Choose ceramic for heavy stock removal.Usually blue, red or purple, and noticeably more expensive. Ceramic grains self-sharpen under pressure, so they cut fast and last far longer — but only if they are worked hard. On light hand sanding they simply glaze. Their place is on belt sanders, coarse random-orbit discs and floor sanding.
- Know garnet and glasspaper for what they are.Garnet is the traditional orange-brown paper, softer than aluminium oxide and gentler on timber, still liked for hand sanding fine work. Glasspaper is the pale yellow sheet sold cheaply; it is obsolete for anything but the roughest work and blunts almost immediately.
- Choose the backing to suit the job.Paper backings, graded by weight from A (light and flexible, for hand sanding contours) to F and heavier (stiff, for machine use). Cloth backings for belts and for anything that has to flex without tearing. Film backings for very fine finishing work, because they are dimensionally stable and give a very even scratch pattern. Mesh or net discs let dust through the whole face rather than through punched holes.
- Choose open coat or closed coat.Closed coat has grain covering the whole surface and cuts fastest on hard materials. Open coat leaves gaps between the grains so soft material has somewhere to go, which is what you want for softwood, resinous timber, paint and filler. Stearate-coated papers add a dry lubricant that resists clogging further — those are the pale, almost chalky-looking ones sold for paint and finishes.
- Match the grit range to the stage.40–60 for stripping and levelling; 80–120 for general shaping and removing machine marks; 150–180 as the finish grit before paint; 220–240 before stain, oil or varnish; 320–400 for denibbing between coats; 600 and above, usually wet, for cutting back and polishing a finish.
- Use the right paper for finishes and fillers.A stearated silicon carbide paper is the correct choice for rubbing down paint, varnish and filler, because ordinary aluminium oxide clogs with soft material within seconds and then burnishes rather than cuts.
- Buy in the sizes and fittings your tools take.Hook-and-loop discs must match the pad diameter and the hole pattern, or extraction stops working. Belts have a direction arrow and a specified length. Sheets for a third-sheet orbital sander come pre-cut or are cut from a roll.
Tips
- The single biggest false economy in DIY is cheap sandpaper. Poor grain, poor adhesive and a weak backing mean it stops cutting in a minute and you spend the time you saved pressing harder.
- Abrasive has a shelf life in a damp shed — the adhesive softens and the grain sheds. Store it flat, dry and out of sunlight.
- Grit numbers are not comparable across standards. European P-graded paper and American CAMI grading diverge noticeably above about 220, so compare within one system.
- Fold a sheet into thirds for hand sanding so the abrasive faces are never rubbing against each other.
Questions people ask
What is wet-and-dry paper made of?
Silicon carbide on a waterproof backing. The grain suits fine finishing and the backing survives being used with water or white spirit, which floats the debris away and stops clogging.
Why does my expensive ceramic paper not seem better?
Ceramic grain needs pressure to fracture and expose fresh edges. Used gently by hand it glazes over and performs worse than aluminium oxide. It belongs on machines that work it hard.
Does the colour tell me what the abrasive is?
Roughly, and not reliably across brands — brown or red for aluminium oxide, dark grey or black for silicon carbide, blue or purple for ceramic, orange-brown for garnet. The pack states the grain if you look for it.