Flatten Waterstones with 220 Grit on Glass

Waterstones cut fast but wear unevenly—dishing in the middle and losing accuracy. To keep them performing, they must be flattened regularly. The simplest method: lap them on 220 grit sandpaper stuck to a flat glass or granite plate. This restores flatness so your plane irons, chisels, and knives sharpen true every time.

Why Flattening Matters

When waterstones dish, your bevels and backs stop meeting evenly. That means rounded edges, weak micro-bevels, and inconsistent honing. A few passes on 220 grit resets the stone flat, ensuring accurate, repeatable sharpening.

Tools & Materials

• 9×11 in 220 grit wet/dry sandpaper sheets
• Thick glass plate or granite reference surface
• Water + drop of dish soap for lubrication
• Pencil for cross-hatching
• Microfiber cloth

Recommended Grit

• 220 grit — Fast cut for flattening stones without glazing or polishing.

Step-by-Step: Flattening Waterstones

1. Mark the stone. Draw a cross-hatch grid on the stone face with pencil. These lines show high/low spots during flattening.
2. Set up 220 grit. Mount 220 grit (25-pack) onto glass with spray adhesive or just water tension.
3. Lap the stone. Move the stone in figure-eights or circles across the sandpaper. Keep even pressure and cover the whole sheet.
4. Check progress. Stop when all pencil lines are gone—this confirms flatness.
5. Rinse & repeat. Rinse both stone and paper often to prevent clogging. Replace paper as soon as it slows down.
6. Ready to sharpen. With a flat stone, your tools will hone evenly across the full edge.

Special Cases

Very coarse stones (220–400): Dish faster; flatten almost every session.
Fine stones (3000+): Flatten less often but still need trueness.
Diamond plates: Don’t need flattening—use them to flatten waterstones instead of sandpaper if available.

Pro Tips

• Always lap under running water or with plenty of spray—slurry cuts better and keeps grit clear.
• Rotate the stone during lapping to prevent leaning one side low.
• Check flatness with a straightedge if in doubt.
• Don’t waste time flattening the full thickness—just the working face.
• Store stones flat and dry to prevent warping.

Aftercare

• Rinse thoroughly after flattening—residual grit scratches tools.
• Dry stones slowly—don’t oven or sun-dry, which can crack them.
• Re-flatten anytime you feel tools rocking during honing.

FAQs

• Why 220 grit? It’s aggressive enough to cut quickly but fine enough to leave a smooth stone face.
• Can I use coarser paper? Yes, but it may leave grooves. Always finish with 220.
• How often to flatten? Coarse stones: nearly every use. Fine stones: every few sessions.
• Will sandpaper wear out fast? Yes—expect to replace sheets regularly. It’s still cheaper than diamond plates.

Video: Waterstone Flattening Demo

Closing: Flat stones = sharp tools. A quick lap on 220 grit over glass keeps waterstones true and your edges razor-ready. Make it part of your sharpening routine.