Handling the paper

Curling clues:
Abrasive paper will curl up and crack if it’s left lying around. To keep the paper from curling, place a weight on it. Or store the paper in the freezer so that heat and humidity won’t affect the adhesive holding the abrasive to the paper.

Flexing paper:
Abrasive paper is usually stiff and brittle, making it tough to fold and likely to leave scuff marks on the work surface. To make the paper more flexible, pull it, with the grit side up, back and forth over the edge of a table or workbench.

Hack it up:
If you cut a lot of abrasive paper, here’s one way to save time and effort. Screw a hacksaw blade to the edge of a piece of plywood; the teeth should point up and jut above the plywood. For a fence, glue or screw a straightedge or ruler along one side of the plywood. Draw lines at often-used intervals for easy measuring.

Types of abrasive paper

Abrasive paper (commonly called sandpaper) is available in a bewildering number of types. Here are the main choices and the jobs that they’re best suited for:

Aluminium oxide: Familiar light grey paper with tough, durable synthetic grains. Best general-purpose paper, but more expensive.

Sand: Inexpensive, but cuts slowly and dulls quickly. Sometimes has different grit size classification system to other papers. Small jobs and sticky surfaces that clog any paper quickly. Otherwise best to avoid.

Garnet: Reddish in colour. Garnet grains fracture during use, exposing fresh, sharp cutting edges; cuts quickly but wears quickly too. Good all-purpose abrasive, particularly for hand-sanding of timber.

Silicon carbide: Black wet-and-dry paper; has hardest grit and removes material very quickly. Can be wet with water or oil to keep it from gumming up. Available only in fine grits. Ideal for very fine sanding, such as between coats of varnish and other finishes. Hard enough to abrade metal.

Stearate: An aluminium oxide paper coated with a zinc or calcium compound and a lower density abrasive distribution to prevent clogging. Fast-cutting and long-lasting. Generally expensive. Extremely good for woodworking, especially on softwoods, which can gum up ordinary papers. Also good for removing loose paint and contaminants.

Grades of abrasive paper

Abrasive paper is classified by a number reflecting the size of the grit particles on it. Higher numbers indicate smaller grains for finer finishing. Here are the common grades of abrasive paper with their grit numbers and uses:

P40-60: (Coarse) Rough sanding and shaping; removing paint. Leaves scratches that can be difficult to remove.

PSO-150: (Medium) Intermediate sanding after rough sanding; sanding on previously painted surfaces.

P180-320: (Fine) Final sanding before applying finish. Smoothing paint.

P400-1200: (Extra fine) Smoothing between coats of paint. Finer grades for finishing surfaces when spray painting over metal.