Imagine a slew of tiny saws and chisels, all working together to strip a surface of debris, old paint, and primer. Each tiny blade working with the next to get the job done. In essence, you’ve just imagined what a sheet of sandpaper looks like close-up in action.
Sandpaper is just one of the many cutting tools you have in your toolbox, though of course you wouldn’t want to try cutting anything with it – instead, it’s meant to refine and hone a project to perfection.
Of Grades, Grits, and Particles
Not all sandpaper is created equally. Commercial grade sandpaper is the most commonly available type of sandpaper. Commercial grade paper is the sort you’ll find at your local hardware store and is typically good enough to handle most projects. Industrial-strength sandpaper is available only through supply houses and is of higher quality than commercial grade paper and can stand up to more rigorous tasks.
But what do the numbers mean? Sandpaper comes in a variety of strengths – called grits – generally ranging from 40 to 600. These grits are the measure of how many abrasive particles (think tiny saws) it takes to fill one square inch of the paper. The higher the grit, the more particles are present and the tinier they are, meaning a finer, more polished surface. The lower the grit, the fewer particles are necessary to fill one square inch of paper and the coarser the final product.
Working Through the Grits
A sanding job requires “working through the grits” – a term used to describe using increasingly finer sandpaper to smooth the surface of the project. 40-60 grit sandpaper is considered coarse and is used to remove heavy-duty debris, like leftover paint. 80-120 grit sandpaper smoothes the surface, removing obvious marks and imperfections. 150-180 is finer sandpaper and is typically used as a final pass before applying sealer or paint. 220-600 is very fine to super fine sandpaper and is typically used between coats of sealer or paint to remove dust flecks, coat imperfections, and as a final buff.
It’s usually sufficient to stop at 150-180 grit sandpaper, unless you’re working with very soft woods or a water-based stain or paint. Softer woods, like pine, require finer grits to get a luster and sheen. Water-based stain or paint can pick up even the most minute scratches, dust particles, and imperfections, and thus require a finer grit sandpaper to look their best.
Beyond the Grade and Grit: Particles
It’s not all about grade and grit, though. The grit on sandpaper is also made from different types of particles.
Aluminum oxide, for example, is a common material and makes for a great all-purpose sandpaper. Aluminum oxide has self-renewing properties. When heat and friction are applied to the paper, the grits fragment. Because it is a friable material, aluminum oxide particles will break off to create newer, sharper grits, lengthening the time needed between switching sheets. This makes aluminum oxide suitable for use on wood, plastic, metal, and fiberglass.
Garnet, a natural abrasive, is not friable or self-renewing and wears out faster. Because of this, garnet isn’t suitable for all materials and it is typically reserved for final finishing work. Garnet also produces a finer finish than aluminum oxide of the same grit.
Other materials, such as silicon carbide and ceramic, are also used. These two are harder than garnet and aluminum oxide, but neither is friable and both are comparatively expensive.
While grit, material, and grade are the most obvious differences between sandpaper, manufacturers are increasingly coming up with new and useful types. By putting some thought into your sandpaper choices and use, you can improve the look of your finished project and greatly increase client satisfaction.