Sandpapers are composed of different materials with different characteristics. A type that's good for shaping wood might not be the best choice for creating a smooth finish on metal. Different sandpapers also tend to work and wear differently. Some wear out quickly, while others can last through multiple tough jobs before losing their bite.
The Nitty Gritty of Sandpaper
The one thing various sandpapers have in common is the grit system. Sandpaper materials are rated for coarseness or fineness by their grit number. The higher the number, the finer the grit, and the less rough the sandpaper. Coarse sandpaper removes material faster but leaves deep scratches. Fine sandpaper removes less material and leaves a smoother surface. Grits can range between 24 for heavy material removal to 2000 and beyond for the gentlest sandpapers.
Aluminum Oxide Sandpaper
Aluminum oxide is synthetic sandpaper that commonly comes in sheets and other forms for hand- and machine-sanding. It is a good all-around choice for sanding bare wood and metal and for painted surfaces. It can provide excellent results when used on a power sander but is equally suited to hand-sanding.
Ceramic sandpapers are composed of synthetic material normally reddish-brown in color. Ceramic sandpapers are extremely durable and hard and are ideal for use with power sanders. This type of sandpaper can be more expensive than others but can produce ideal results for rough sanding. It lasts four to six times longer than other good sandpapers and is excellent when deep wood removal is required.
Garnet is a natural sandpaper material that wears rapidly, although it provides a finer finish as it wears down. This type of sandpaper is normally a reddish or golden brown color. It is ideal for hand-sanding and lighter, finer work. It tends to be less expensive than other sandpapers and is commonly sold in sheet form. Garnet abrasives have hard, sharp edges that fracture during sanding, creating fresh cutting edges, but the sandpaper overall wears relatively quickly.
Silicon Carbide Sandpaper
Silicon carbide sandpaper often features a waterproof backing. Usually blue-gray or black in color, it can be used on wet or dry surfaces and is ideal for sanding metal, sanding between coats of finish, and polishing smooth surfaces. It is less likely to clog than other sandpapers, and it provides excellent results on metal, plastic, and fiberglass. Wet-sanding with water helps to reduce clogging and extends the life of the abrasive. It is great for sanding metal for repainting, prior to adding a primer coat.
Alternatives to Sandpaper
Steel wool is a great material for removing sludge or rust from most surfaces before finishing. Steel wool is rated by a number scale to indicate coarseness. Grade 4 is the most coarse; grade 0000 is the finest. Grade 0000 is so fine it can be used to clean window glass.
Other abrasives include diamond stones and water stones, for sharpening knife blades and other tools; scrapers (steel cutouts), for finely shaving wood; and abrasive sponges, for working in corners or on oddly shaped pieces where sandpaper can't reach.