Abrasives - Definition Selection and Use

What is an abrasive, how does an abrasive work, how is an abrasive made, and how do I select the right abrasive for the job?

Longtime woodworker

I've been a woodworker all my life and more recently became interested in trying my hand at some metalworking. Sandpaper and other abrasives are important to those and many many other trades and crafts.

There is a lot to this abrasives topic and I've barely begun to scratch the surface (sorry) in researching what's available and how it works.

What is an abrasive?

An abrasive is a substance used for abrading, grinding, polishing, lapping, made of natural materials such as Emery, Garnet, Flint, and Crocus, and of manufactured or electric furnace materials such as Aluminum Oxide, Silicon Carbide, and Alumina Zirconia.

What is sandpaper?

Sandpaper is a coated abrasive product made up of essentially three components, a backing, an adhesive, and an abrasive grain.

The abrasive grain is glued to the backing with at least two coats of adhesive, a making coat and a size coat. The making coat is the first adhesive coat which adheres the abrasive grain to the backing, to provide proper anchoring and orientation of the abrasive grain. The size coat is the second adhesive coat applied which unites with the making coat and insures the final anchoring of the grain and proper total adhesive level to the finished product.

A sandpaper in which the abrasive grain covers approximately 50% to 70% of the coated surface is called open coat. An open coat helps to retard loading of sticky or gummy materials such as softwoods or paint.

Antistatic sandpapers are increasingly used for woodworking to reduce static electricity buildup and allow sanding dust to be better collected by a dust control system.

See Klingspor's comprehensive Abrasive Terms Dictionary for a complete list of terms relating to abrasives.

Shelf life of sandpaper

It looks like I have a tendency to buy my sandpaper in too large a quantity. I'm learning that sandpaper a limited shelf life, particularly the glues and tapes used to make the joints in sanding belts. Klingspor and others warranty their belts and sticky back discs for one year and recommend that you buy no more of these items than you can use in six to eight months. They also recommend you store them in a heat and humidity regulated space as both those factors can adversely effect the adhesives as well as the backings. That probably explains the problems I've had in recent years with belt breakage. My shop is only heated intermittently now that it is less active and belt breakage has become a big problem.

Glazing when sanding resinous woods

Here's what Klingspor says about this problem.

There is nothing on the market that you could spray on a belt that would deter glazing due to loading. If your belts are polyester (inherently waterproof) or if they've been chemically treated to be waterproof, you can wash them and clean them out somewhat. Some shops are using a product called "Purple Power®" that is available at any retailer. It's ecologically safe so disposal is not a problem, and does seem to buy them some extra life on their belts. One other thing I might suggest is that when you are sanding soft, gummy or resinous woods, be sure your abrasive belts are Open Coat. This means that 50-70% of the grain has been removed from the backing so that as you sand and particles get packed up in the grain, they will have room to fall back out. Closed coat abrasives have 100% of the backing coated in grain and should be used for hard woods or metals only. They, of course, offer the best cut and finish because there are no gaps in grain coverage, but if you load the belt up before it's completely used, less life and finish will occur.

Tags: Finishing - Metalworking - Woodworking - Supplies - Tools