Why the finish starts with the sanding

It is tempting to think of sanding as the tedious bit you rush through to get to the satisfying part — the oiling, the waxing, the first brushstroke of paint. In practice, the reverse is true. Every scratch left behind by a coarse grit will still be there under your finish, magnified by the way light catches a varnished surface. Paint will not hide poor preparation; it will announce it.

Sanding is not really about rubbing wood down. It is about replacing deep scratches with progressively finer ones until the surface is uniform enough that the eye reads it as smooth. Done properly, it takes an hour or two on a typical piece of furniture and transforms how the timber accepts colour and sheen.

Getting your abrasives and grits right

Skip the cheap glasspaper. Aluminium oxide abrasives stay sharp far longer and clog less, which matters more than the few pence you save on a bargain pack. You want a sequence of grits, and the key rule is not to jump more than roughly one step at a time — going from 80 straight to 240 just burnishes the scratches you were trying to remove.

• 80 grit — for rough sawn timber, badly damaged surfaces, or stripping back old finish.
• 120 grit — the workhorse. Use it to remove the scratch pattern left by 80.
• 150 or 180 grit — plenty for most painted work and general joinery.
• 240 grit — the sensible stopping point before staining or oiling bare hardwood.
• 320 grit and finer — for sanding between coats of finish, not for bare timber.

One warning worth heeding: on dense hardwoods such as oak or maple, going beyond 240 on bare wood can close the grain and leave stain looking patchy. Softer timbers like pine benefit from a light 240 pass but bruise easily under heavy pressure, so treat them gently.

Sanding by hand: slow, deliberate, with the grain

Hand sanding is not a punishment. It is the only way to get into mouldings, around joints and along profiled edges without flattening them. Wrap your paper around a cork block for flat faces — fingers alone create hollows — and use a dowel or a folded strip for coves and curves.

The fundamentals are simple but easy to forget:

• Work along the grain wherever possible. Cross-grain scratches are almost impossible to remove later.
• Use light pressure and let the abrasive cut. Bearing down generates heat, dulls the paper and rounds over crisp edges.
• Move methodically, overlapping your strokes, and brush or vacuum the dust away before changing grits so you are not dragging coarse particles over a finer surface.
• Keep the paper clean. Once it glazes over and stops cutting, it is doing nothing but polishing and can glaze the timber too.

A cabinet scraper earns its keep here as well. On hardwood, a well-turned scraper removes tear-out and leaves a surface that needs only a light 180 pass.

Using a random orbital sander well

A random orbital sander will save you hours on flat panels, but only if you resist the urge to press down. The machine needs to float across the surface; your hand is there to guide it, not to add weight.

Fit the grit you need, start the sander on the workpiece rather than in mid-air, and keep it moving in slow, overlapping passes — roughly half a pad width per sweep. Do not tip it onto its edge, which digs a groove, and do not linger in one spot. Let the tool come to a complete stop before lifting it off, or the spinning pad will catch an edge and chew the corner.

Connect dust extraction if you can. A vacuum or extraction hose keeps the abrasive cutting, keeps the surface visible and keeps your lungs considerably happier. If you are working indoors, a mask and an open window are the minimum; fine wood dust is not something to be casual about.

Work through the grits with the machine, then finish by hand with a block, going with the grain. It takes two minutes and removes the faint swirl pattern the sander leaves behind.

Raising the grain, filling and sealing

Bare timber, particularly softwood, will lift its fibres when it meets water-based stain or paint, leaving a furry surface. Get ahead of it: wipe the sanded wood with a damp cloth, let it dry completely, then sand lightly with 240 to knock the raised fibres back. You will be rewarded with a much smoother first coat.

Open-grained timbers such as oak and ash benefit from a grain filler if you want a glass-smooth finish. Press it across the grain with a squeegee, let it flash off, then sand back with 320. Alternatively, a coat of sanding sealer does a similar job while stiffening the surface for the next pass.

The final check before paint or oil

Before you commit to a finish, wipe the whole piece down with a tack cloth or a cloth barely dampened with white spirit, and look at it in raking light — a lamp held low and to one side will reveal every swirl and scratch that daylight hides. Run your fingertips across the surface; they will find what your eyes miss.

Touch up any problem areas with the finest grit you have used so far, dust off thoroughly, and then give the wood the finish it deserves. The sanding is the part nobody sees. It is also the part everyone notices.