Believe it or not, choosing the right sandpaper can become confusing. In fact, it has gotten so confusing that "Sandpaper" is now referred to as "Abrasive Technology." It can be confusing because there are so many different offerings. Some of the differences include the backings, adhesives, and minerals used in layout of the paper. Another difference is the anti-loading features: open vs. closed coated and even super size coat.
The most important thing to do before choosing an abrasive to use is to properly diagnose the job requirements and understand which paper will do the job correctly. The construction of your abrasive (disc, belt, sheet or whatever) is pretty simple.
Backing: A flexible or semi-rigid backing (paper, cloth, film) to which the minerals are attached with adhesive. There is a designation for flexibility and durability ranging from A-weight (most flexible) to F-weight (least flexible).
Adhesive: Abrasives usually have two adhesive layers.
a. Make Coat--Initial layer of adhesive to anchor the mineral to the backing.
b. Size Coat--Secondary layer of adhesive to lock the mineral in place.
Abrasive Minerals: There are five basic types of minerals:
a. Aluminum Oxide--brown or blue. Is the industry standard for metal, wood, composites, and plastics.
b. Silicon Carbide--black. Is used for sanding primers, sealers and paints, non-ferrous metals, and final finishing.
c. Ceramic Aluminum Oxide--A synthetic mineral that is very durable with extremely uniform crystalline structure.
d. Alumina Zirconia--Primarily for heavy stock removal of metal and wood.
Diagnosing Sandpaper Problems
The biggest complaint about sandpaper is that its wearing out too quickly. But, this could mean a number of things and its important to diagnose what is really wearing out. Often times (as funny as it sounds) it helps to pull your sandpaper out of the trash and really take a hard look at it.
1. Is the abrasive mineral dulling too quickly? You need a more aggressive mineral.
2. Is the backing falling apart? You need a more durable backing.
3. Are the minerals falling off of the backing? Your adhesive is failing.
4. Is the abrasive so clogged with junk that it no longer cuts? You need to look for an Open Coat paper or maybe even one with an anti-loading agent (3M Fre-Cut).