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Abrasives 101
Abrasive Fundamentals for the Beginner

Learn more about the safe use of abrasive products

This is a basic guide to abrasives and there uses for both the beginner & tradesman. The first thing about abrasives is the abrasive media itself.

Media
There are all forms of abrasive media materials used in crafts and industry today. Soda ash, glass beads, silica (sand), cut glass, garnet, aluminum oxide, silicon carbide, ceramics, zirconia, and hardest of all diamonds.

Abrasive blasters ( Sandblasters)
Utilize all of these but the ceramics and diamonds, due to cost. Sand is rarely used as a blasting abrasive due to health concerns. The media is propelled by compressed air to remove rust, paint, and other materials from the base material in preparation of refinishing.

Sandpaper.
Sandpaper is the most common abrasive and sometimes the most confusing. There is no one type fits all. There are 3 major components to sandpaper.

Media
Media or "Grit" in sandpaper consists of mainly four of the above materials. Garnet, aluminum oxide, silicon carbide, and zirconia. Garnet being the softest, and zirconia being the hardest. There are some "sandpaper" disks that use diamonds bonded to copper backing, but these are highly specialized products, and not in common use. Each media has its own characteristics, as well as pros and cons for each intended use. See the bottom of the page for more information about the different media's and their properties. The size of the individual media particles determine the papers grit size. The lower the number the bigger the particles. Here is a chart of common sizes and there uses.

Bonding Agents
Bonding Agents attach the grit particles to the backing material. There are several bonding agents used in sandpaper. The two most common are glue, used in cheap commercial / retail grade products, and resins, used in industrial / professional grade products.

When the media is bonded to the backing it is bonded in two common patterns. "Open coat" is when there is more space between the individual particles of media allowing less loading (waste particles clogging the paper) and faster material removal. Open coat paper grits dig deeper in the work material and allow for faster material removal.
"Closed Coat" is when the media particles are bonded in a denser pattern. With the space between the particles being smaller the grit can't dig as deep leaving a finer scratch pattern, and a finer finish in less time. Most closed coat abrasives have a lubricant "Grinding Aid" to reduce heat from friction.

Backing Materials
The two most common backing materials for sandpaper are paper and cloth. Backing papers come in several thicknesses called "Weights" and are differentiated by letters, A being the thinnest, and W being the thickest.

Higher grits of paper usually come in A weight (for light sanding and home use), B weight (for rough industrial use) and C Weight (for use on light power sanders and blocks). The heaver weight papers are used for the lower grit media's because the size of the media particles, and the friction of the sanding action would destroy the lighter backing papers.

Cloth backed "sandpaper" is used in products intended for power tools. Disk sanders, belt sanders, and rotary sanders must use heavy cloth backed abrasives.

Media type "Pros & Cons"

As mentioned before there are no "one type fits all" when it comes to abrasive media's.

Garnet
Garnet is a natural abrasive that is used mostly in the facility painting and wood working fields. It is the least expensive media, and for the most part has been replaced by aluminum oxide. It is not a friable material and tends to wear out quickly due to this characteristic. It is still used by wood workers because it will produce a smoother finish on wood than aluminum oxide of the same grit size. It is also best for final finishing of wood.
+ Pros inexpensive, and produces wonderfully finish on wood.
- Cons Non friable, loads fast, and wears out quickly.

Aluminum Oxide
As mentioned above aluminum oxide or A/O has replaced garnet as the most common type of abrasive used in wood working today. It is high friable (the heat and friction of the sanding process fracture or "break" the individual particles thus creating a new cutting edge) This self "Resharpining" process to last longer on wood than most other sandpapers.
+ Pros Easily friable, less loading, and lasts longer on wood
- Cons Too friable for use on hard materials like hard metal and hard composites

Silicon Carbide
Silicon carbide (sic) is a friable much harder than both garnet and aluminum oxide. It's used on harder materials like metal, composites, stone, heavy wood sanding and shaping. It's also used on heavy grade sanding belts and disks.
= Pros It's hardness makes it tougher to stand up to harder material
- Cons it's too hard for wood to fracture its particles and will wear out faster

Zirconia
Zirconia is not a friable material, and is the hardest abrasive used in sandpaper. It's main uses is in the lowest grits used in high grade sanding belts and disks for leveling and shaping of wood. It's also used on abrasive "Flap Disks" used on side grinders to clean metal, and smooth welding seams.
+ Pros Tough and long lasting
- Cons Expensive and not suitable for most applications.