Sandpaper and Abrasives Guide: Grit Progression, Backing Types, and When to Stop

Understanding Grit Numbers

Grit numbers indicate the size of the abrasive particles. Lower numbers are coarser (bigger particles, more aggressive). Higher numbers are finer (smaller particles, smoother finish). A 60-grit abrasive has particles roughly 0.010 inches across; a 220-grit has particles about 0.003 inches across.

Coarse grits (40-80) remove material fast — flattening rough lumber, removing old paint, and shaping wood. Medium grits (100-150) smooth the surface after coarse sanding and remove tool marks. Fine grits (180-220) prepare surfaces for finishing. Very fine grits (320-600) sand between finish coats.

Never skip more than one grit step in a progression. Going from 80 to 220 leaves 80-grit scratches that 220 cannot efficiently remove — you end up sanding forever. The standard wood progression is 80, 120, 150, 180, 220. Each step removes the previous grit's scratches efficiently.

Abrasive Types

Aluminum oxide is the most common abrasive for wood sanding. It is tough, self-sharpening (particles fracture to expose new cutting edges), and works well on both hardwood and softwood. Most sandpaper you buy for general woodworking is aluminum oxide.

Silicon carbide is harder and sharper than aluminum oxide. It cuts glass, metal, and finishes effectively and is the standard abrasive for wet sanding between finish coats. Available in very fine grits up to 2000 for polishing.

Garnet is a natural abrasive that dulls during use, which can actually be an advantage — the dulling particles produce a burnished surface that accepts stain more evenly than aluminum oxide. Furniture restorers and finishers sometimes prefer garnet for final sanding before stain.

Ceramic and zirconia alumina are aggressive, long-lasting abrasives used in belt sander belts and flap discs. They handle high-pressure sanding of metal and hardwood where softer abrasives wear out quickly. Overkill for hand sanding but excellent for power tool applications.

Backing and Format

Paper backing ranges from A-weight (thin, flexible, for hand sanding curves) to E-weight (thick, stiff, for belt sanders). C-weight is the most common hand-sanding paper — flexible enough to wrap around blocks but stiff enough to lay flat on surfaces.

Cloth backing is more durable and tear-resistant than paper. Sanding belts, flap discs, and shop rolls use cloth backing because paper would shred in seconds on power tools. More expensive but lasts proportionally longer.

Pressure-sensitive adhesive (PSA) discs stick directly to sanding pads. Hook-and-loop discs attach with Velcro-type fasteners for quick changes. Hook-and-loop costs more per disc but saves significant time on random orbit sanders where you change grits frequently.

Sanding sponges conform to curved and contoured surfaces that flat paper cannot reach — molding profiles, turned parts, and rounded edges. The foam core compresses to match the surface shape. Available in coarse through fine grits.

Technique and Common Mistakes

Sand with the grain on wood. Cross-grain sanding produces scratches that show prominently under stain and finish. Final sanding strokes should always follow the grain direction, even if initial aggressive sanding crosses the grain for faster material removal.

Apply even, moderate pressure. Heavy pressure digs the abrasive into the surface unevenly, creating valleys and burning. Let the abrasive do the cutting — your job is to guide it consistently across the surface.

Change paper when it loads (fills with dust) or dulls. A loaded sheet slides instead of cutting and actually polishes the wood surface closed, which prevents stain from penetrating evenly. Fresh paper cuts cleanly and consistently.

Know when to stop. For oil-based finishes, sand to 180 grit. For water-based finishes, sand to 220 grit (the raised grain from water-based products shows imperfections that oil-based hides). For bare wood that will be stained, 150 to 180 grit is usually sufficient — too smooth and the stain has nothing to grab.

Frequently Asked Questions