- What makes sandpaper so abrasive?
- Why you should care about the abrasive grain you choose for your project.
- Aluminum Oxide – The Versatile Powerhouse of Abrasives
- Silicon Carbide – Self-Sharpening And Great For Beautiful Finishes And Glass
- Ceramic Alumina – Long Lasting, Great For Metal Finishing
- Alumina-Zirconia – The Grittiest Of Them All
- Abrasive Grains Cheat Sheet
If you’re looking to create the best version of your woodworking or metal projects, no doubt sanding will be a key part of that process, whether you’re rough sanding to remove jagged edges, de-burr, in preparation for gluing, or if you are in the finishing and polishing stages.
Each of these steps clearly requires different sandpaper grits to get the best results, but the grain type will also impact your overall results – and believe it or not, it may even be best to change types depending on the material you’re working with and the stage you’re at. So, clearly, choosing the right type of abrasive will be critical, and could mean the difference between a high-quality finished product and an amateurish-looking piece, in addition to increasing the life of your sandpaper, getting the best results for your sanding/polishing/finishing stage, having a faster, cleaner and cooler (reduced heat/friction) sanding job.
But, what to pick? It can certainly be overwhelming to choose, once you start to look into all the types of coated abrasives on the market (not to mention just on our website!), even if you’re an experienced sander. In this article and accompanying materials, we’ll detail the most common abrasive grains we offer and some of the conditions and materials that they work best for.
And, if you’re more of a visual learner, skip to the bottom of this article and download the infographic with all this information.
(Note that most of these products are fairly versatile, designed in a lab for particular conditions and you may have other factors to consider, such as budget, time and versatility of materials/projects, type of sanding process/machine, product format requirements, so use this only as a guide – don’t take it as gospel.)
So, wait… If it’s not actually sand, what makes it so abrasive?
If you’re reading this article, it may not come as much of a surprise to you that the term “sandpaper” is actually a misnomer, as the grittiness of sandpaper is not actually made from sand, like at the beach, and this grit is not always even attached to paper.
So, if it’s not actual sand, then what is it? And, what are the differences between the various abrasive materials?
Sandpaper is actually a type of coated abrasive, meaning, it is made from some type of abrasive “grain”, such as the types we are going into in this article, which is affixed to some kind of backing – often paper, cloth, plastic, or even foam sponges or mesh. There may or may not be other added fillers or coatings, such as stearation.
These days, there are several types of abrasive materials used on sandpaper products, including a few natural rocks/minerals and a handful of synthetic substances, manufactured in labs, each with their own advantages and disadvantages.
The most common natural minerals used in abrasives are emery and garnet, while four common manmade types are silicon carbide, aluminum oxide, ceramic alumina and alumina- zirconia. Each varies in longevity, coarseness/aggressiveness, amount of friction required, friability, cost, ideal application, available grit sizes and coating and what formats of products they are available on, such as disks, sheets, or belts.
Why you should care about the abrasive grain you choose for your project.
Before we discuss each of these grains, it’s important to consider why these characteristics matter. First, and let’s be real, does anyone really enjoy sanding? If you do, let us know!! …But for the rest of us, sanding can be a bit time consuming, boring and even a pain on the hands, so, wouldn’t it be great if we could make the process more efficient, and more effective? Other than making it merely tolerable with some headphones and great music, we can often speed up the process by using the proper type of abrasive product for our application with proper technique, which will save time and resources.
Additionally, using the proper abrasive grain / project material combination, as well as proper technique and pressure, can also help to reduce sanding costs by allowing your products to last longer. One way this happens is thanks to using products that create less friction, and therefore less heat, which causes the abrasives to cut more effectively, not burn your material and clog up less. Furthermore, the friability, or the characteristic that allows grains to break to form new, sharp edges (self-sharpening), allows you to go longer before the sandpaper wears out.
Now that you know why it’s important to choose the right grain for the project, let’s discuss each of the four options we have available.
Aluminum Oxide – The Versatile Powerhouse of Abrasives
The most versatile of the synthetic abrasive grains, Aluminum Oxide commonly comes in three types: pink, white and brown, or semi-friable. Aluminum oxide is a chemical compound of aluminum and oxygen formed by fusion and then broken down and sorted by grit size through a series of mesh screens (see this video for an example). Each of the types measures at about 9 on the Mohs Hardness Scale, a measurement scale that defines how resistant materials are to scratching. The Mohs scale places common minerals on a scale of one through ten, starting with Talc at the bottom and Diamond at ten.
Most of the time, the type of aluminum oxide will not be mentioned on our website, however each type is more suitable for different types of sanding.
Aluminum oxide-based coated abrasives can be used in belt sanding, power sanding or for hand sanding applications, and are available on a range of backing materials with both open and closed coatings.
Pink aluminum oxide is available in coarse through fine grit products on a variety of different backings and in a variety of formats. It generally works well for softer substrates, such as wood, for aggressive sanding.
White aluminum oxide is available in coarse through fine grit products on a variety of different backings and in a variety of formats. It generally works well for wood, providing a cooler sanding experience for aggressive sanding on wood and lacquers, as well as for use between coats of finish on your woodworking projects.
Brown, or semi-friable, aluminum oxide is the most common type of aluminum oxide, because of its versatility. It is available in coarse through micro grit products, coming affixed to a variety of different backings and in a variety of formats. It generally works well for harder substrates, such as metal (particularly softer metals), fiberglass, drywall, painted/primed surfaces and wood. When used in coarser grits, from 80 to 180, with a medium pressure/tension, this grain works well for wood and metal stock removal, allowing the grains to break and re-sharpen, making the product last longer. When used in finer grits, around 600-800, this material is great for finishing and polishing metal.
Silicon Carbide – Self-Sharpening And Great For Beautiful Finishes And Glass
Silicon Carbide, another popular grain type, is a semiconductor containing silicon and carbon and is produced through carbothermal reduction. It is the hardest common abrasive grain, other than diamond, and measures at a 9.5 on the Mohs Scale of Hardness.
While silicon carbide tends to wear quicker than aluminum oxide, it is also sharper and more friable, therefore it is still a long-lasting product and is ideal for uses on harder materials, rougher surfaces, and for polishing, due to its hardness and sharpness. It is best for metals (particularly harder metals) and is the only grain that can be used on glass, stone and marble. Silicon carbide is also effective on MDF and cork.
Silicon carbide is frequently used in wet sanding applications, such as polishing stone and marble, as well as automotive polishing applications. In coarser grits, this abrasive is good for removing rust, deburring metal and glass, refinishing wood flooring (cutting through/removing old finish). Silicon carbide can also be used to sand between finishing coats in woodworking projects, so it is common to use aluminum oxide for rough sanding of raw wood, and switch to silicon carbide when in the finishing stages of the same project.
Being a pretty versatile, and relatively forgiving, abrasive grain, silicon carbide is available on belts, disks, sheets, sponges and for use in power sanding and hand sanding applications.
Ceramic Alumina – Long Lasting, Great For Metal Finishing
Ceramic alumina is a long-lasting synthetic grain produced directly as a grain through an aqueous dispersion of fine aluminum oxide powder. While it can often be more expensive, it lasts longer and provides a cooler sanding experience than aluminum oxide. Often simply referred to as ceramic, this grain works best on metal, stainless steel in particular, and requires a hard surface/pressure in order to activate the friability. While it can be used on wood, it will be very aggressive ploughing through the wood instead of cutting it. This could lead to a very uneven scratch pattern which will result in a poor finish.
Alumina-Zirconia – The Grittiest Of Them All
Alumina-Zirconia, also referred to as zirc or zirconium, is produced by die-casting and is typically available in only coarser grits, up to 120, on belts and disks for power sanding units. Because this grain is best for heavy stock removal in mills, an initial sanding of raw woods, and removing burrs from very hard metals, it is mostly available on heavy cloth backings with mostly open coats, to provide a sturdy product with space for a lot of material to accumulate. This allows the products to withstand medium to high pressure and avoid clogging too quickly. If you have a lot of rough sanding to do for raw woods, rust or other metal work, choosing zirconia might be the best option, in spite of a potentially higher price, because it will last longer, be more friable, and provide a cooler sanding experience than aluminum oxide.
As you can see, there are certainly many aspects that will influence which abrasive grain, and therefore, which “sandpaper” will be best for your particular application. While aluminum oxide is the most common, and generally most affordable of our products, choosing another material, or combination of materials and grits, might ultimately be more cost effective, longer lasting and even more effective at the job, even if you only work with one base material. For instance, if you are someone that frequently works with jagged wood, bringing it all the way to a finish, or if you work with reclaimed metal parts for cars, it may make sense to mix, therefore, choosing different grains for coarser applications verses finishing and polishing.
Abrasive Grains Cheat Sheet
Here is a sample of a great infographic, designed to help make all this information much simpler, and easier to understand.
Click here to download a full resolution PDF of the infographic.
If you would like further information or assistance, we welcome you to contact our customer service or sales representatives.