SANDPAPER GRIT indicates abrasive particle size. HIGHER number equals SMALLER particles equals SMOOTHER finish; LOWER number equals LARGER particles equals FASTER material removal but rougher surface. COMMON GRIT GRADES and APPLICATIONS: 40-60 GRIT (extra coarse) for heavy material removal; stripping paint; removing finishes; rough shaping. 80-100 GRIT (coarse) for flattening rough wood; removing minor finishing; preparing for next grit. 120-150 GRIT (medium) for general smoothing; preparing for finer grits; first sanding step for most projects. 180-220 GRIT (fine) for final sanding before staining/finishing; reasonable smoothness. 240-320 GRIT (very fine) between coats of finish; fine sanding. 400-600 GRIT (extra fine) between coats of varnish/lacquer; preparing metal for polishing. 800-1000 plus GRIT for polishing; very smooth surfaces; metal polishing; auto body work between coats. 1500-3000 plus GRIT for automotive paint polishing; mirror finishes.
Sanding technique: progress through grits sequentially because skipping grits leaves deeper scratches not removed by the finer grits; typical progression: 80, 120, 180, 220 for wood projects, sometimes finer for finishing. SAND WITH the GRAIN of wood because cross-grain scratches are very visible after staining (oil and stain emphasize scratches). Apply EVEN PRESSURE. Use a SANDING BLOCK (cork, foam, hard rubber) for flat surfaces because it keeps sandpaper flat and removes material evenly; using bare hands creates uneven pressure. Use a SANDING SPONGE for curves and details; flexes to follow contours. CLEAN dust between grits because leftover coarse grit will scratch the new finer-grit surface; vacuum or tack cloth. Final sanding with finest grit, then thoroughly clean. On end grain, sand to FINER grit than face grain because end grain absorbs more stain.
Abrasive materials: ALUMINUM OXIDE is most common general-purpose; brown/red; for wood and metal. SILICON CARBIDE has sharp friable particles that renew themselves; black; for wet sanding, finish sanding, metal, glass. GARNET is natural mineral; orange/brown; for wood, especially hardwoods. CERAMIC is high-end; durable; for power sanding heavy work, hardwoods, metal.
Sandpaper formats: SHEETS (9 by 11 inch) cut to size for hand sanding or sanding block. BELTS for belt sanders. DISKS for random orbit sanders (5 inch and 6 inch common, hook-and-loop attachment). ROLLS for hand sanding or industrial. MESH/SCREEN for drywall sanding (allows dust to pass through). SPONGES for curves and edges.
Power sanders: RANDOM ORBIT SANDER has disk that rotates and orbits with minimal swirl marks; most versatile general sander. BELT SANDER uses sanding belt for aggressive material removal. ORBITAL FINISHING SANDER (1/4 sheet) has rectangular pad with vibration only (no rotation) for fine sanding. DETAIL SANDER (mouse) has triangular pad for corners/tight spaces. DRUM SANDER (large stationary) for thicknessing or smoothing large panels. DISK SANDER (bench-mounted) for shaping edges. SPINDLE SANDER has vertical spinning drum for inside curves.
Sanding safety: DUST MASK or RESPIRATOR (wood dust is a carcinogen, especially hardwoods like walnut, cherry; MDF/particleboard contains formaldehyde adhesives; pressure-treated wood contains toxic chemicals); EYE PROTECTION (particles fly); DUST COLLECTION on power sanders is important; gloves not necessary for hand sanding because they can interfere with power sander dust collection. WET SANDING (for finishes and automotive paint) uses water or oil as lubricant; minimizes clogging; produces ultra-smooth surface; silicon carbide sandpaper.