Why the Grit Sequence Matters

A scratch is only removed by a slightly shallower scratch. That is the whole principle behind working through the grits. Jump from 80 straight to 180 and you have not smoothed the surface — you have simply made the coarse scratches smaller and harder to see, until the first coat of finish goes on and every one of them stands up and waves at you. Each grade removes the marks left by the one below, so the ladder only works if you climb every rung.

The rule of thumb worth remembering: never jump more than one grade, and never more than about 50 per cent in grit number. 120 to 180 is fine. 80 to 180 is a shortcut that will cost you time.

What Each Grit Is Actually For

• 60–80: coarse stock removal — flattening rough boards, lifting out planer marks and old dents. Leaves deep scratches that must be sanded out.
• 100–120: the first refining stage, where the coarse marks start to disappear and the surface levels properly.
• 150–180: general preparation, and a sensible stopping point for oil and hard wax finishes.
• 220–240: the standard finish before most film finishes, stains and water-based lacquers.
• 320–400: between coats, and on end grain, which always wants one grade finer than the face.
• Above 400: rarely useful on bare timber. Very fine grits burnish rather than cut, and a closed, polished surface can take stain unevenly.

Working Through the Grades Without Fooling Yourself

Mark the surface with a light pencil grid before each grit. When the grid has gone, you have sanded evenly and can move on. It sounds fussy; it saves a great deal of guessing.

With a random orbit sander, let the machine do the work. Leaning on it does not cut faster — it loads the paper, heats the timber and encourages swirl marks. Keep the pad flat, keep it moving, and label your sheets so you always know which grit is on the tool.

Change abrasive more often than feels economical. Worn paper glazes rather than cuts, polishing the fibres and compressing the surface, which can leave a finish drying patchy or a dye refusing to take. Fresh paper at 150 beats tired paper at 240 every time.

Finish each grit by hand, sanding along the grain with a cork block or felt pad. A dozen strokes in the direction of the grain removes the small orbital swirls that show under raking light.

Clear the Dust, Every Single Time

Dust from a coarser grit gets dragged along by the finer paper and grinds fresh scratches into the work, so remove it before you change sheets.

• Vacuum with a brush attachment first.
• Follow with a tack cloth, folding and turning it as it loads up.
• On open-grained or oily timbers such as oak, teak and iroko, wipe with white spirit and let it flash off.
• If you use compressed air, do it outside and wear a mask.

A deliberately damp cloth — water popping — raises crushed fibres so the next grit slices them off cleanly. It is worth doing before your final sanding stage on anything headed for a water-based dye, as it stops that fuzzy texture appearing after the first coat.

Inspection: Seeing What Your Fingers Miss

Do not trust a casual glance. Hold a lamp low and to the side; raking light throws a shadow across every scratch and swirl. Turn the workpiece through different angles rather than walking around it.

Wipe a small patch with white spirit or methylated spirits for a preview of the finished colour — it reveals scratches that vanish on dry timber. Run a bare hand over the surface, then repeat with your hand inside a thin plastic bag; the bag snags on fibres your skin slides straight over. Check edges, curves and end grain now, not after the first coat. If you find a scratch, drop back a grade or two, work it out properly and climb the ladder again.

Edges, End Grain and Awkward Shapes

Edges round over far faster than you expect, and a sander rolling across an arris will soften it in seconds. Work edges with a block and keep the face flat, or commit to a deliberate, even chamfer rather than a random wobble.

End grain is denser and drinks finish more greedily, so take it one or two grades finer than the surrounding faces — 320 where the faces stopped at 240 — and sand it longer than feels necessary. For mouldings and turned work, wrap paper around dowels, use shaped blocks and foam pads, and fold a crisp edge for inside corners. A freshly burred card scraper deals with tear-out and difficult grain faster and cleaner than any abrasive.

Match the final grit to the finish: 180 is plenty under oil, 220 to 240 before most film finishes, and finer only where the product specifically asks for it. Climb the ladder properly, clear the dust and inspect under a decent light, and the finish will reward you.