Sandpaper Grit Progression

Sandpaper grit numbers run backward from what the number seems to suggest — a higher number means finer abrasive, not more of it — and skipping too many steps between grits is the single most common way a sanding schedule fails to remove the previous step's scratch pattern, leaving visible cross-grain marks under a finish that a coat of oil or varnish makes far more visible than they looked dry.

The working progression

A typical furniture-finishing schedule runs roughly: 80 or 100 grit for initial stock removal or leveling a rough surface, 120 for the first real smoothing pass, 150 or 180 as an intermediate step, 220 as the common "ready for finish" stopping point on most species, and 320 or higher reserved for finish-sanding between coats of a film finish rather than for bare-wood prep. Open-pored, coarse-grained species (oak, ash) often don't benefit from sanding much past 220 before finishing, since the wood's own grain texture becomes the limiting factor on smoothness rather than the sandpaper; tight-grained species (maple, cherry) can show a visible improvement in finished smoothness sanded to 320 or beyond before the first coat.

Why skipping grits causes visible problems

Each grit step is meant to remove the scratch pattern left by the previous, coarser grit — jumping from 100 straight to 220, for instance, leaves 100-grit's deeper scratches un-removed underneath a surface that merely looks smoother to the touch at 220. Those un-removed deeper scratches are invisible on bare, dry wood but become highly visible once a finish (especially an oil or a stain, which pools in low spots) is applied, because the finish makes contrast between the true surface and the residual scratch bottoms far more visible than dry wood does. A safe rule of thumb is not skipping more than about 50% of the grit number per step — 100 to 150 is fine, 100 to 220 usually isn't.

Sanding with the grain, and why cross-grain scratches show worst

Every grit step should follow the same direction, parallel to the grain, because a scratch running across the grain reflects light differently from the surrounding wood fiber and stands out under a finish even at a fine grit — a single stray cross-grain pass at 220 can be more visible in a finished piece than a whole coarser-grit pass that stayed parallel to the grain. Random-orbit sanders reduce but don't eliminate this risk, since the orbital motion still imparts some cross-grain scratching at each stage; a final hand-sanding pass parallel to the grain at the finest grit used is common practice specifically to clean up whatever cross-grain marks the machine step left behind.

Grit type matters alongside grit number

Aluminum oxide is the general-purpose abrasive for hand and power sanding wood across most of this progression; silicon carbide, sold at finer grits, is more commonly used for sanding between finish coats (wet-or-dry paper) than for bare-wood stock prep, since it cuts more slowly on raw wood but produces a finer, more consistent scratch pattern useful for leveling a cured finish film without cutting through it. Using the wrong abrasive type for the stage — silicon carbide for aggressive stock removal, for instance — wastes both time and paper relative to using aluminum oxide at the coarser end of the schedule.

Dust collection matters more here than the grit numbers might suggest

Fine sanding dust, especially from 220 grit and finer, is small enough to stay airborne far longer than the coarser dust from initial stock removal — see /reference/dust-collection-cfm-requirements/ for what a random-orbit sander or a stationary sanding station actually needs for real dust capture, since the health risk from fine wood dust scales with how small and how airborne the particles are, not with how much total material is being removed at that stage.

Where the progression starts depends on what tool left the surface

A surface coming off a hand plane or a well-tuned jointer/planer combination often doesn't need to start the sanding schedule at 80 or 100 at all — a clean planed surface can reasonably start around 120 or 150, since there's no rough milling texture to level, only tool marks and any minor snipe to remove. Starting a sanding schedule too coarse on an already-smooth machined surface wastes both material and time removing a texture that was never actually there to begin with; matching the starting grit to the surface's actual condition, not to a fixed habitual starting point, is worth checking case by case.

Species-specific quirks worth knowing

Some species sand unevenly because of density swings within the growth rings — Douglas-fir's alternating hard latewood and soft earlywood bands (also relevant to its workability under a hand plane, a related but separate issue) sand at different rates under the same grit and pressure, which can leave a subtly wavy, corrugated surface if sanding isn't done with a firm, even backing pad rather than bare-handed. Species with this kind of density variation benefit from a harder sanding block or a machine pad rather than hand-sanding freehand, which tends to follow the softer earlywood down and leave the harder latewood standing slightly proud.