Choosing the correct Sandpaper for the job
Here are several different types of abrasives used for sandpaper, including:
Aluminum Oxide: This abrasive is the most common all-purpose sandpaper material for home or workshop use. Aluminum oxide sandpaper is economical and suitable for most materials – including wood, metal, paint, plastic, and fiberglass. One advantage of aluminum oxide is that it’s friable, meaning the particles fracture to expose new sharp edges as you sand, which makes the sandpaper last longer.
Garnet: An inexpensive sandpaper abrasive, garnet is used mainly on wood. Garnet is a natural material that grinds down smooth with use. This allows garnet sandpaper to produce a velvety surface in fine woodworking projects, though it also tends to wear out rather quickly.
Silicon Carbide: This synthetic abrasive is gray or black in color and often backed with a waterproof material for use in wet sanding. Since it’s harder than many other abrasives, silicon carbide is mainly used for sanding hard materials – such as metal, plastic, or fiberglass – as well as sanding between coats of paint or finish. It’s generally not used for sanding wood, except on wood floor sanding machines.
Ceramic: A very hard abrasive, ceramic is generally used for removing large quantities of wood, such as with a belt sander. Ceramic sandpaper generally doesn’t produce a very smooth surface.
Emery: Used for sanding, polishing, or removing rust from metal. Emery usually has a cloth backing to make it more durable and flexible.
Once you’re decided which kind of abrasive you need, the next step is to choose the right grit. Sandpaper grits are graded according to the size of the abrasive particles, with lower numbers for larger particles and higher numbers for smaller particles.
You can find the grit size on the package label and printed on the back of each sheet of sandpaper. Grit is generally classified as follows:
Coarse: Grits less than 60. Coarse grit sandpaper are used for removing material rapidly, such as when shaping corners or stripping paint.
Emery sandpaper for metal.
Medium: Grits ranging from 80-120. Medium grit sandpaper are used to smooth rough surfaces, remove scratches, and prepare surfaces for paint or finish.
Fine: Grits ranging from 150-220. Fine grit sandpaper are used for final smoothing of surfaces before application of finish, or for sanding between coats of finish.
Superfine: Grits above 220. Superfine grit sandpaper are used to smooth or polish surfaces between coats of finish.
When sanding, start with the lowest grit required, then work your way through successively finer grits, with each finer grit used to remove the scratches created by the grit before. For example:
When stripping and refinishing a piece of wood furniture, you might start with 60 grit sandpaper to remove the old finish, then work your way through 80, 120, 180, and finally 220 to smooth the wood.
To sand a piece of new unfinished furniture, you could begin with 120 grit sandpaper and work up to 220.
For sanding between coats of finish, you would use 220 grit or higher sandpaper.