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Sanding is one of the most common construction and repair tasks you have to do around your home. It is the final step that determines the final appearance of your work. Done right, it makes your paint job perfect. Done badly, it shows through the most skillfully applied finish. Sanding is also one of the easiest jobs to do right, if you select the correct abrasives. Use them properly and it’s almost impossible to do a bad job. However, the wrong abrasives can make it almost impossible to get good results no matter how hard you work with them. 

Sandpaper can be identified by three things: the type of abrasive particles on its surface, the grit (or coarseness) of each particle, and the actual amount of abrasives on each sheet. 

The two most common types of sandpaper are coated with abrasives made from flint and garnet. Flint is cheaper and this makes it a logical choice when working on surfaces like paint and soft, gummy woods that clog the paper quickly. Garnet grits form a tougher, longer-lasting surface and are a better choice when working on hardwoods like walnut and oak. 

Silicone carbide is the hardest abrasive grit generally available for consumer use. These abrasive sheets are ideal for sanding nonferrous metals, composition boards and plastics. When applied to waterproof papers or cloth backing materials, silicone carbide can also be used for wet sanding with water or mineral oil for rubbing down varnish, polyurethane and lacquer finishes. 

The closest thing to an all-purpose paper is aluminum oxide paper. It can be used on wood, metal, plastics and fiberglass. 

The grit size of the abrasive on a sheet of sandpaper is identified by a number on the backing material. The higher the number, the finer the grit. Extremely coarse papers with relatively open coats of abrasives – each granules spaced out from the others – remove heavy layers of paint, enamel or varnish from relatively rough surfaces. They’re fine for preparing the surface of a house for painting, but would be wrong for taking even a heavy paint buildup from fine interior paneling or furniture. 

Medium grits remove light stock from wood and prepare walls for painting inside the house as well as smoothing rougher sanding for finer finishing. Fine and very fine grits carry this process the rest of the way for a perfect finish, removing sanding scratches to make a surface ready for primer or sealer. 

With most sandpapers you have a choice of open or closed coatings. A closed coat covers the entire sheet with abrasive particles while a more open coat may give no more than 50 percent or 70 percent coverage. Spacing the grits far apart makes the sandpaper cut more slowly because there are fewer grits to do the job, but the paper doesn’t load up with paint or gummy wood. 

As for sanding techniques, to finish wood smoothly, sand with the grain. Plastics have no grain, but some of them melt when heated by friction so the surface smears rather than smoothes. Fiberglass sands well, but the dust contains tiny glass fibers, so you should wear a dust mask for protection.