Bench / Glossary / Sanding Grit Progression: Why Skipping a Step Costs More Than It Saves
Sanding Grit Progression: Why Skipping a Step Costs More Than It Saves
A grit sequence is not a list of abrasives to own, it is a chain of scratch sizes where each step exists only to erase the one before. Break the chain and you spend longer sanding, not less.
The scratch has to be erased, not just covered
Abrasives cut scratches, and the size of the scratch is the grit number. A 120-grit scratch is roughly 100 microns wide; a 180-grit scratch is roughly 40; a 220 is about 25. The next step in the sequence only works because its scratch is smaller than the previous one and cuts across it at an angle, replacing a big scratch with several small ones.
Skip from 80 to 220 and you have not removed the 80-grit scratch. You have polished the tops of the ridges either side of it and left the scratch sitting in the bottom of its own valley, where no amount of 220 will reach it. It only shows up after the finish goes on, because finish fills the valley and the light catches the difference.
That is why skipping a step feels faster for the first ten minutes and then costs an hour of going back.
The four-stop ladder that works on most furniture
80 grit for stripping residue and heavy damage. Only on solid timber, never on veneer, and only where a scraper has already taken the worst of it.
120 grit for flattening. This is the grit that does the real work and the one most people under-use. Everything after it is refinement; if the surface is not flat at 120 it will not be flat at 220.
150 to 180 for removing the 120 scratches. Two steps here rather than one because a jump of 60 points leaves scratches that a 220 cannot lift.
220 as the stopping point for most film finishes. Finer than that and the finish has nothing to key into; on open-pored timbers it also burnishes the surface and stops the finish soaking in evenly.
Where the ladder changes
On veneer, start at 150 and never touch 80. Veneer is 0.6 mm thick and a single careless pass with 80 grit on a random-orbit will go through it.
On pine and other softwoods, stop at 180. Soft earlywood compresses under finer grits and the surface ends up looking glazed, which then takes finish unevenly.
Between coats of finish, use 320 or a grey Scotch-Brite pad, and only enough to knock the nibs off. This is not part of the wood-sanding ladder at all; it is a separate, much lighter operation with a different purpose.
Comparison
- Jumping 80 to 220 on a walnut top: 25 minutes of sanding, then a visible scratch pattern under the first coat, then 50 minutes back at 120.
- Running the full ladder: 55 minutes total, no rework.
- Measured with a 10x loupe after each step, the 80-grit scratches were gone at 180 in the full sequence and still visible at 220 after the jump.
General practice, not a rule for every timber. Dust control and product data sheets come first; this page is information only.