Sanding is part of many home improvement projects, from woodworking to paint preparation. But if you’ve ever looked through the sandpaper section at the home center or the paint store, you might be confused about all the different grits, abrasives and other terminology you’ve run into. Here are a few tips to help clear up some of the mystery.
Abrasives
The material that does the actual sanding work is what’s known as an abrasive. The abrasive is bonded to a backing, typically paper. So when we think of sandpaper, we typically think of tiny particles of sand that are adhered to a paper backing, which is obviously where it gets its name. But there are actually thousands of different combinations of abrasive materials, backing materials, and bonding materials to hold the two together. Luckily, for home improvement use, you’ll need to concern yourself only with a couple of them: aluminum oxide, garnet, silicon carbide and ceramic.
Aluminum Oxide: Aluminum oxide is one of the most common abrasives, and works well for sanding both wood and metal. As you sand, the aluminum oxide particles crack and break off, which means that sharp new points are constantly being exposed. This helps the aluminum oxide sandpaper to last longer than other types of sandpaper.
Garnet: Garnet sandpaper is a good choice for woodworking. The particles don’t crack off the way the aluminum oxide does, which means that the sandpaper dulls as you use it. So while garnet paper wears out faster, it tends to create a smoother surface on wood than aluminum oxide paper of the same grit. This can be a definite advantage for the final finishing of woodworking projects.
Silicon Carbide: Sandpaper with a silicone carbide abrasive is very hard, harder than either aluminum oxide or garnet. This hardness makes it a great choice for sanding metal, for paint removal, and for use on plastic and fiberglass. Usually not the best choice for wood.
Ceramic: Ceramic particles are very hard but not overly sharp, and are also on the expensive side. They work especially well for the fast removal of material, particularly in woodworking. They’re most commonly found on the belts used for belt and drum sanders, and some types of disk sanders.
Grit
Besides the type of abrasive material you’ll be using, the next thing to concern yourself with is the grit. The grit of the sandpaper refers to how fine or how coarse it is. And in one of those oddities of construction, the lower the grit’s number is, the rougher the sandpaper is, and the higher the number is, the finer the sandpaper is.
Coarse: Coarse paper is generally considered to be in the 40- to 60-grit range. This grit would be used for the initial surfacing of rough wood, for rough shaping and for paint removal.
Medium: Medium sandpapers fall within the 80- to 120-grit range. They’re typically used for the next step in smoothing wood surfaces.
Fine: Fine sandpapers have grits of 150 to 200, and are usually the final paper used before painting or staining.
Very Fine: Very fine sandpaper is usually in the 220- to 240-grit range. This is commonly used to remove imperfections, or to roughen a surface between coats of finish.
You always want to begin with a grit that’s just coarse enough to begin removing material from the surface you’re sanding. In other words, don’t use a paper that’s any coarser than it needs to be, since you’ll be introducing additional grooves into the surface that you’ll just have to sand out later. On the other hand, using 150-grit paper to try to remove paint will be a waste of time, since the paper will clog almost immediately.
Work your way up through progressively finer and finer papers until you achieve a surface that’s smooth enough for what you need. You might need to use just two different grits, or you might have to work through four or even five.
Open-coat and closed-coat sandpaper
These are a couple of other terms you might run into at the home center. Closed-coat sandpaper has abrasive that covers the entire surface of the paper. That additional abrasive means that you’ll be able to remove material faster, but it also means that the paper will tend to clog more quickly.
With open-coat sandpaper, the abrasive covers about 60 percent to 70 percent of the surface of the paper, with more open space in between the particles. This makes the paper less aggressive to sand with, but also makes it more flexible and less likely to clog up. Open-coat sandpapers are a good choice for sanding wood, and especially for paint removal.
