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.
Make Coat--Initial layer of adhesive to anchor the mineral to the backing.
Size Coat--Secondary layer of adhesive to lock the mineral in place.
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.
Abrasives sometimes load-up with dust before the mineral is actually worn-out.
1. Open vs Closed Coat: Open Coats have less minerals to create more space between abrasives to reduce loading. While Closed Coats have 100% mineral application with hardly any voids. Closed coats should have a longer life--as long as it does not load up with dust (a major problem with composite and woodworking abrasion).
2. Supersize Coat: There are some coatings applied to the abrasive that work as anti-loading agents ( 3M's FreCut )
Diagnosing Sandpaper Problems
The biggest complaint about sandpaper is that it 'wears out' too quickly. But, this could mean a number of things and it's 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's Fre-Cut).