80-120-grits are considered medium, and used primarily for smoothing a surface and/or removing smaller imperfections and marks. Grits in the 150-180 range are labeled as fine and useful for a final sanding pass before a primer coat, for example. 220-240-grits are designated as very fine and are good for sanding between coats of primer or sealer. 280-320-grits are labeled extra fine and are good for removing dust spots or fine scratches between finish coats. 360-600-grits are considered super fine, and are used for sanding a surface to remove some luster or surface blemishes and finer scratches. 800-2,000-grits are designated ultra fine and are usually reserved for final color-sanding on paint or for final finishing of metal that’ll remain uncoated. OK, so now that we’ve covered the basics of grit, we’ll look at the difference between commercial- and industrial-grade abrasives.

There are three main components to sandpaper: the abrasive grit, the backing material, and the bonding agents that attach the grit to the backing (be it discs or paper). Industrial-grade sandpaper uses higher-quality (heavy-duty) components as well as tighter manufacturing tolerances. Industrial-grade sandpaper also features harder and sharper grit that is less likely to break down or wear out, better bonding agents that hold the abrasive to the backing material, and heavier-duty backing that is less likely to tear or wear through.

Choose your weapon

Metalworkers and body men use a sanding procedure sometimes called “going through the grits.” Not to be confused with a good old southern breakfast, it really refers to the process of sanding where one uses progressively finer pieces of sandpaper to get a smooth finish. By going through the grits, each progressive sanding step removes the scratches left over from the previous step. Skipping grits to save time is not necessarily a good idea as you’ll usually end up sanding longer just to remove the scratches left by the previous grit. You’ll always want to start with a low, coarser grit, and then work your way up to a finer grit.

There are also different types of sandpaper, specifically “open coat” and “closed coat.” Open-coat sandpaper has gaps and open spaces between the grits that help prevent clogging by giving the removed material space so it can separate or fall away from the paper or disc. Closed-coat is better for sanding metal finishes as it’s more aggressive, but clogs a bit easier on softer materials like primer or some body fillers.

So, though not a complete course on abrasives, hopefully this’ll give ya a bit of a background on a common tool we all use without much thought, and a basic guide to sandpaper and sanding disc choices.

SOURCE
Summit Racing Equipment
PO Box 909
Akron
OH  44398
800-230-3030
330-630-0240
www.summitracing.com
Eastwood Company
263 Shoemaker Road
Pottstown
PA  19464
800-343-9353
http://www.eastwood.com
Wet Wedge
Irvine
CA
949-295-5824
www.wetwedge.com