Sandpaper

What it is

Sandpaper is a manufactured abrasive: a backing (paper, cloth, or film) coated with hard particles that cut tiny grooves in a surface. By progressively scratching and then removing those scratches with finer grits, you flatten, shape, or polish materials like wood, paint, drywall compound, plastic, and metal. It’s available as sheets, discs, belts, and sponges for hand or power-sanding.

How it works

Each abrasive grain is like a microscopic cutting tool. Coarser grits have larger, fewer particles that remove material quickly and leave visible scratches. Finer grits use smaller particles to refine the surface. Moving through a logical grit progression (for example, 80 → 120 → 180 → 220) reduces scratch depth at each step until the surface is ready for finish or paint.

Common DIY uses

• Woodworking: Leveling joints, smoothing edges, prepping bare wood for stain or finish, and sanding between finish coats.
• Paint prep: Scuffing glossy surfaces for better adhesion, feathering chipped paint, and smoothing primer.
• Drywall: Knocking down ridges on joint compound and achieving a paint-ready wall.
• Metalwork: Removing rust, deburring sharp edges, polishing, and between-coat sanding on spray finishes.
• Auto and plastics: Wet sanding to refine scratches and orange peel on finishes or to shape plastics without clogging.

Types and variations

Abrasive minerals

• Aluminum oxide: Durable, self-renewing grains for wood, paint, and metal. A great all-purpose choice.
• Silicon carbide: Very sharp, fast-cutting; excels on metal, plastic, fiberglass, and for wet/dry use. Common in waterproof papers.
• Garnet: Cuts cleanly on wood and tends to leave a fine scratch pattern; wears faster than aluminum oxide. Good for hand-sanding bare wood.
• Ceramic/zirconia: Extremely tough grains for heavy stock removal; common on belts and discs for aggressive sanding.

Grit numbers (how coarse or fine it is)

• 24–36: Heavy stripping and shaping, grinding off thick finishes or rust.
• 40–60: Rapid stock removal, shaping edges, leveling uneven boards.
• 80–100: General smoothing after shaping, removing planer or saw marks.
• 120–150: Pre-finish smoothing on wood, scuff-sanding primer.
• 180–220: Final sanding before stain/clear coat; between finish coats.
• 320–400: Refining finishes, light polishing, denibbing dust nibs.
• 600–2000+: Wet sanding for metalwork, auto finishes, and high-gloss polishing.

Note: You’ll see CAMI (e.g., 120) and FEPA “P” designations (e.g., P120). Numbers are close but not identical; stick to one system during a project if possible.

Backings and coatings

• Backings:
  • Paper (A–D weight): Flexible to stiffer; common for sheets.
  • Cloth (X/J weight): Tough and tear-resistant; used on belts and for curved surfaces.
  • Film: Very flat and durable; ideal for uniform scratch patterns on finishes.
• Coatings:
  • Open-coat: Fewer grains per area; resists clogging on soft woods and paints.
  • Closed-coat: Fully covered; cuts fast on hard materials but clogs more easily.
• Bond: Resin-over-resin is standard for heat resistance and durability.
• Stearated papers: Have a lubricant to reduce clogging on paint and resinous woods.

Formats

• Sheets (9x11 in): Hand sanding and blocks; easy to cut to size.
• Discs (PSA or hook-and-loop): For random orbital sanders.
• Belts: For belt sanders; aggressive stock removal.
• Sanding sponges: Flexible for profiles and between-coat sanding.
• Detail triangles/strips/rolls: For specialty sanders and custom sizes.

Wet/dry

Waterproof sandpaper (usually silicon carbide) can be used with water or mineral spirits. Wet sanding keeps dust down, reduces clogging, and leaves a finer scratch, useful for finishes and metal.

How to choose the right sandpaper

1. Match the grit to the task: Start as fine as possible while still effective. For painted trim touch-ups, 180–220 may be enough. For leveling a table top, 80 or 100 is a safer start than 40, which can leave deep scratches.
2. Pick the right mineral: Aluminum oxide for general work, silicon carbide for wet sanding and metals, garnet for hand-sanding wood, ceramic/zirconia for heavy removal.
3. Consider clogging: Use open-coat or stearated for soft woods and paint. Switch sheets as soon as cutting slows.
4. Choose a suitable backing: Film-backed discs for consistent finish on cabinetry; cloth-backed belts for hogging off material; paper-backed sheets for everyday use.
5. Power tool interface: Hook-and-loop discs are quick to change and resist heat; PSA (peel-and-stick) hold very flat but are harder to remove.

Tips for using sandpaper

• Use a sanding block or flat pad: Keeps surfaces flat and prevents grooves. A cork, rubber, or foam block works well.
• Follow the grain on wood: Sanding across the grain leaves visible scratches that finishes highlight.
• Progress through grits: Remove the previous grit’s scratches before moving on. Skipping grits often leaves hidden scratches that show under finish.
• Light, even pressure: Let the abrasive cut. Too much pressure clogs paper and creates swirl marks or heat.
• Keep it clean: Tap the sheet, use a rubber cleaning stick on belts/discs, or vacuum dust. Clean paper cuts faster and cooler.
• Dust control and safety: Wear eye protection and a dust mask or respirator (N95 or better). Use dust extraction on sanders. Avoid dry sanding suspected lead paint; test homes built before 1978 and follow safe practices.
• Label and reuse: Save partially used sheets by grit; worn 120 can act like a fine scuff paper for finish work.
• Between coats: Lightly sand finishes with 220–320 and a soft pad to remove nibs, then wipe with a tack cloth or vacuum.

Common mistakes to avoid

• Skipping grits: Deep scratches reappear after finishing. Step through logical increments.
• Too coarse for the job: Coarse grits save time initially but add time later removing scratches.
• Over-sanding edges: Edges thin quickly; use fewer strokes and a backer pad.
• Using dull or clogged paper: It burns, polishes, and leaves swirls. Change it as soon as cutting slows.
• Wrong abrasive for material: For example, garnet on metal wears out fast; silicon carbide or aluminum oxide is better.
• No dust collection: Dust hides defects. Vacuum or wipe between grits to check your progress.

Practical examples

• Refinishing a dining table: Scrape or strip finish, then sand 80 → 120 → 180. Lightly mist and raise the grain, then final sand at 180–220 before stain. After the first clear coat, denib with 320 and recoat.
• Repainting a door: Feather chipped areas with 120, scuff the whole surface with 180–220 for adhesion, prime, then lightly sand with 220 before the finish coats.
• Smoothing drywall joints: Start with a drywall sanding screen or 120 paper on a pole sander. Use a light touch, then finish with 150–220. Consider wet sanding with a sponge for less dust.
• Removing rust from garden tools: Use 80–120 aluminum oxide to cut rust, then 220 to refine. Wipe clean and apply a rust inhibitor or light oil.
• Polishing a spray finish: After curing, wet sand with P800 → P1200 → P1500 using soapy water and a foam pad, then buff.

Related terms

• Abrasive: The cutting particles on sandpaper.
• Grit: The size rating of abrasive particles.
• Sanding block: A handheld backer that keeps paper flat.
• Random orbital sander: A power tool that reduces swirl marks by combining rotation and vibration.
• Belt sander: A powerful tool for rapid material removal.
• Sanding sealer: A fast-drying finish used to ease sanding between coats.
• Scuff sanding: Light sanding for adhesion between coats.
• Emery cloth/steel wool: Alternative abrasives for metal and finishing tasks.