Why Grit Sequence Matters More Than Grit Alone

Sandpaper is not one tool but a ladder, and timber only becomes truly smooth when you climb it in order. Jump from a coarse paper straight to a fine one and you will trap scratches beneath a polished surface that show up the moment stain or paint lands on top. Work through the grades and those scratches are removed in turn, leaving grain that feels silky and takes a finish evenly.

In the UK, most abrasive paper and cloth is sold to the P-grade system — the higher the number, the finer the grit. A sheet marked P80 is coarse, P240 is fine, and the gap between them is where all the useful work happens. The golden rule is simple: never skip more than one grade as you move up. Each sheet should erase the scratch pattern left by the one before it, not fight against it.

Coarse Grits: Earning the Right to Be Gentle

Coarse papers, roughly P40 to P80, are for serious removal. They flatten raised glue lines, ease proud joints, strip back old finish and take down the worst of a rough-sawn board. On a reclaimed plank that has spent years outdoors, a pass with P60 is often the only thing that will touch the surface.

Use coarse grits sparingly. They cut fast and leave deep, half-moon swirls that take real effort to erase later. A few sensible habits keep you out of trouble:

• Wrap the paper around a cork or rubber block — fingers alone create dips and hollows in the surface.
• Sand with the grain wherever you can. Across the grain, the coarse scratches are far harder to remove.
• Let the weight of the block do the work. Pressing hard loads the paper with resin and dulls the grit.
• Stop as soon as the high spots are level and the old surface is gone. Coarse grit has done its job.

Medium Grits: Where the Surface Comes Good

Medium grades — P100 to P150 — are the workhorses of any workshop. This is where you remove the scratches left by the coarse paper, flatten the grain and bring the timber to an even, consistent tone. After a proper pass with P120, a board stops feeling furry and starts feeling like wood.

On softwoods such as pine or spruce, this is also where you deal with raised grain. Dampen the surface lightly with a clean cloth or a fine mist of water, let it dry, and the fibres will stand up. A light sanding at P150 or P180 knocks them flat so they do not rise again under a water-based stain or primer.

Keep the paper clean as you work. A quick tap of the block or a brush with a stiff hand-brush clears the dust so the grit keeps cutting. This is also the stage to check your work in raking light — a low lamp across the surface reveals any scratches or hollows a straight-on glance will hide.

Fine Grits: Preparing for Stain and Paint

Fine grits, from P180 to P240, are about preparation rather than shaping. Once the surface is flat and even, these papers refine it just enough to accept a finish without burnishing the grain so hard that stain cannot penetrate.

This is where the choice of finish changes your approach. For stain, stop at P180 or P220. Going finer can polish the timber to the point where pigment sits on top rather than soaking in, giving a patchy result. For paint, a slightly toothy surface is your friend, so P180 is usually ideal as a key. For clear oils and waxes, a final pass at P240 gives you the smoothest possible base.

Always sand the final grit with the grain and finish with a couple of light, sweeping strokes along the whole length of the board. Those last strokes set the direction of the grain and leave the cleanest possible surface.

Beyond P240 and Between Coats

Very fine papers — P320, P400 and up — look tempting, but they have a narrow use in furniture making. Over-sanding can close the pores of the timber and leave a glassy surface that resists stain, oil and varnish alike. Reach for them only when you are refining a film finish, not the bare wood.

A more useful skill is sanding between coats. Once a primer, varnish or lacquer is dry, a light pass with P320 or P400 — by hand, with a very light touch — flattens the nibs and dust flecks and gives the next coat something to grip. Wipe away all the dust with a tack cloth before recoating, or you will simply sand the debris back into the finish.

Building a Simple, Sensible Kit

You do not need every grit on the shelf. For most UK craft and DIY projects, a small, focused set covers everything from a rough plank to a paint-ready panel:

• P60 or P80 — stripping old finishes and levelling rough or reclaimed timber.
• P120 — erasing coarse scratches and bringing the grain to an even tone.
• P180 — the keying grit for paint and the stopping point for stain.
• P240 — final smoothing before oil, wax or clear finish.
• P320 or P400 — for flatting between coats of finish, used sparingly and by hand.

Buy decent paper, whether in sheets, rolls or as discs for a random orbital sander, and change it the moment it stops cutting. Blunt paper glazes the surface, burns the timber and wastes your time. Fresh grit, worked in the right order, is what turns a rough board into something worth finishing — and it is the quiet step that makes every project that follows look considered.