Sandpaper and Abrasives Guide
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The term sandpaper refers to a number of different types of abrasives which can have several different types of backing materials and come in several different forms. No matter the sanding job you have to do, you can find a specially made abrasive to help. Sanding products you can find at your local home store include: sanding belts, tape, discs, cylinders, sheets and abrasive sponges that flex to follow the contours of decorative molding and other irregular surfaces.
About Abrasive Materials
There are a few types of abrasives used to make sandpaper in the US: almandite, a natural mineral that is red in color, aluminum oxide which is a gray–brown color and silicon carbide which is iridescent black and the hardest of the three. Almandite is a red garnet and the sandpaper made with it is sometimes called garnet paper. This type of abrasive is used on soft materials like wood but is not hard enough to cut materials like metal. Use aluminum oxide paper for hard surfaces like metal and silicon carbide for metals, stone and wet/dry sanding.
Sandpaper Grades
Sandpaper is rated based on the size of the grains of abrasive used. Twenty–two screen sizes, from 12 openings per square inch to 600 are used to sort the grains. The size of the grains determines the coarseness of the sandpaper. These ratings are not always used by the manufacturer to label sandpaper for sale. The terms fine, medium and coarse will often be the only rating used to identify grit density on a sandpaper package. Generally speaking, the term fine is used for abrasives from about 150 to 220 grit, medium from about 80 to 120 grit and coarse for about 36 to 50 or 60 grit.
While the grit size is determined by screen size the density of abrasive grains per square inch can vary between open and closed coat. Open coat sandpaper has about 30 to 50 percent open space with no grains of abrasive. This open space decreases the tendency of sanding dust to collect between the grains. Closed coat sandpaper has very little space between grains and will glog or "load" with sanding dust very quickly. Open coat sandpaper is plenty abrasive even with fewer grains and will last thru many more uses than closed coat, so it's the best choice. Fortunately, open coat is the most common type you will find at your paint supplier.
Sandpaper Backing Materials
Backing materials for abrasives are another consideration when choosing sandpaper. The backing used to make abrasives can be paper, cloth or fiber. Paper is available in four weights: A, C, D and E, with A being the lightest and therefore thinnest. Some sanding discs and floor sanding machine papers are backed with the heaviest, E grade paper. For wood sanding the best paper weight to look for is a C. The A weight is very thin and too fragile for most wood sanding but is well suited for use with silicon carbide abrasives and wet/dry sanding. D is used with very coarse grit paper of about 40 and below as well as sanding discs and industrial grade sanding sheets. Sanding belts are made using a type of fabric backing for flexiblity.
Sandpaper for DIY Projects
You can buy a small package of 10 sheets of sandpaper in varying grits at any home or paint store and these are usually a good choice for the average do–it–yourselfer. If you plan to do a lot of sanding of wood and prep work for painting consider buying a sleeve of 50 sheets of 120 grit paper. This is a good medium grit that will do most jobs around the house. No matter the size of the package you buy you should keep the unused paper in the cardboard container it comes in to help keep it dry and clean. Also be sure you keep the package in a dry place like a wood drawer. Avoid storing in damp basements and other such places where moisture can ruin the sandpaper.
