Like duct tape, sandpaper is one of those handy-dandy instruments that fits almost endless applications and is a venerable member of our 'emergency fix-it' tool kit. But how much do we really know about our abrasive friend?
Grading systems
There are three grading systems for abrasives (the proper title for sandpaper).
- FEPA: These are the most common abrasives worldwide, and are indicated by the P that precedes a number on the backside of your sandpaper sheet. In this grading system, the grit of sandpaper is determined by the specific range of grain sizes used in its manufacture.
- CAMI: Used exclusively by US abrasives manufacturers, this system determines what grit an abrasive is by the average particle size used in its fabrication.
- Micron: Gauges an abrasive by each particle's diameter in micrometers for precision not found in other abrasives.
Grit size
In all but Micron-graded abrasives, the larger the number is, the finer the grit. For example, in the case of FEPA-graded sandpaper, P24 would be much coarser than P500. Coarser sandpaper is best suited for jobs where aggressive removal of material is necessary. If you have an old picnic table covered in several layers of paint, using a coarser grit will get the job done much faster than using a finer grit.
However, if you are preparing an unfinished woodworking project to accept stain, you will want to use a finer grit abrasive to ensure the smoothest finish.
Generally, you'll want to use several grits of abrasives on a project—starting with a coarser grit sandpaper and working your way incrementally towards a very fine sandpaper before applying a finish.
To apply your newfound sandpaper knowledge, take a peek at The Home Know-It-All's suggestions on repairing and refinishing wooden window frames.
Until next time,
The Home Know-It-All
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