If you want to create the best woodworking or metal project possible, there's no doubt that sanding will be a key part of the process, whether you're rough sanding to remove jagged edges, deburring, preparing for gluing, or in the finishing and polishing stages.
Obviously, each step requires a different sandpaper grit size for best results, but the type of grit will also affect your overall results – believe it or not, depending on the material you're working on and the stage you're at, it's best to switch up the type. So, obviously, choosing the right type of abrasive is crucial and can mean the difference between a high-quality finished product and an amateurish one, in addition to extending the life of your sandpaper, getting the best results during the sanding/polishing/finishing stages, and making sanding jobs faster, cleaner, and cooler (less heat/friction).
But what to choose? Once you start looking at all the types of coated abrasives on the market, the choices can certainly be overwhelming, even if you're an experienced sander. In this post and accompanying materials, we'll go over the most common abrasive grains we offer and some of the conditions and materials they're best suited for.
Aluminum Oxide – A Versatile Abrasive
Aluminum oxide is the most versatile synthetic abrasive and is generally available in three types: pink, white and brown, or semi-friable. Aluminum oxide is a compound of aluminum and oxygen that is formed by melting and then broken down through a series of mesh screens and classified by particle size. Each type has a hardness of about 9 on the Mohs scale, a measurement that defines how well a material resists scratching. The Mohs scale ranks common minerals from 1 to 10, with talc at the bottom and diamond at the tenth.
Aluminum oxide-based coated abrasives can be used for belt sanding, power sanding or hand sanding applications, and are available in a range of backing materials with both open and closed coatings.
Pink aluminum oxide is available in a variety of coarse to fine grits for a variety of different substrates and in a variety of formats. It is typically used on softer substrates, such as wood, for aggressive sanding.
White aluminum oxide is available in a variety of coarse to fine grits for a variety of different substrates and in a variety of formats. It is typically used on wood, providing a cooler sanding experience for aggressive sanding of wood and paint, and can also be used between coats on woodworking projects.
Brown or semi-friable aluminum oxide is the most common type of aluminum oxide because it is so versatile. It is available in coarse to fine grit sizes, affixed to a variety of different backings, and in a variety of forms. It is generally suitable for harder substrates such as metals (especially softer metals), fiberglass, drywall, painted/primed surfaces, and wood. This grit is excellent for deburring wood and metal when a coarser grit (from 80 to 180) is used and moderate pressure/tension is applied, causing the grit to break up and re-sharpen, making the product last longer. When a finer grit (about 600-800) is used, this material is excellent for finishing and polishing metals.
Silicon carbide is another common abrasive grit type, which is a semiconductor containing silicon and carbon produced by carbothermic reduction. It is the hardest common abrasive grit other than diamond, with a Mohs hardness of 9.5.
While silicon carbide wears faster than aluminum oxide, it is also sharper and less brittle, so it is still a durable product and is ideal for use on harder materials, rougher surfaces, and polishing due to its hardness and sharpness. It works best on metals (especially harder metals) and is the only grain that can be used on glass, stone, and marble. Silicon carbide also works well on medium density fiberboard and cork.
Silicon carbide is often used in wet sanding applications, such as polishing stone and marble, and in automotive polishing applications. Coarse grits of this abrasive are suitable for rust removal, deburring metal and glass, and refinishing wood floors (cutting/removing old finishes). Silicon carbide can also be used to sand gaps between finish coats in woodworking projects, so it is common to use aluminum oxide for rough sanding of raw wood and switch to silicon carbide during the finishing phase of the same project.
Silicon carbide is a very versatile and relatively forgiving abrasive grain that can be used on belts, discs, flakes, sponges, and in both power sanding and hand sanding applications.
Ceramic aluminum oxide is a durable synthetic grain that is made directly from a water dispersion of fine aluminum oxide powder. While it is generally more expensive, it is more durable than aluminum oxide and provides a cooler sanding experience. This grain, often simply referred to as ceramic, is best used on metals, especially stainless steel, that require a hard surface/pressure to activate the brittleness. While it can be used on wood, it will plow through the wood very hard rather than cut it. This can result in a very uneven scratch pattern that leads to poor results.
As you can see, there are certainly many aspects that influence which abrasive grain, and therefore which "sandpaper", is best for your particular application. While aluminum oxide is our most common product and is generally the most affordable, choosing another material or a combination of materials and grits may end up being more cost-effective, longer-lasting, and even more effective at the job, even if you only use one base material. For example, if you often work with sawn wood that is sanded all the way down to the surface, or if you work with recycled metal parts from cars, it may make sense to mix things up, so choose different grains for coarser applications rather than finer and polishing.
