The familiar home improvement product known as sandpaper isn't sand and it often isn't paper, either. Today, most sandpaper consists of cloth or paper backing material impregnated with abrasive particles such as aluminum oxide or silicon carbide.
Sandpaper Grits: Moving From Coarse to Fine
To use sandpaper properly, you must know how to choose the right sandpaper grit. Sandpaper grits are categorized according to the coarseness of the abrasive particles used.
In general, the process of preparing any surface for painting or finishing involves sanding with progressively finer grits until you reach the desired level of smoothness. Use sandpaper that is too coarse, and the surface will be too rough to paint or finish smoothly, or you may sand away fine detail on a furniture piece.
Sanding with sandpaper that is too fine will require a lot of sanding and effort to get to the desired results.
As a result, choosing the right sandpaper grits and using them correctly is something of an art form. You need to hit a sweet spot that's neither too coarse nor too fine.
|Sandpaper Grit Guide|
|60-80||Extremely coarse; best for removing large amounts of wood and rounding off corners.|
|100-150||Medium grit; good for general purpose sanding.|
|180-220||Fine; used to roughen surfaces for painting or as a first passthrough for later sanding with ultra-fine grits.|
|320||Ultra-fine; helps achieve a nearly glass-smooth texture.|
What Is Sandpaper Grit?
Sandpaper grit is sized by a gauge number, with lower numbers signifying larger, coarser grits. For example, #24- or #40-grit sandpaper is a very coarse, rough sandpaper, while the #1,000-grit paper is extremely fine with very small abrasive particles.
The grit number of sandpaper is almost always clearly printed on the back of the sandpaper itself. Grit numbers range from #24 all the way up to #1,000 although most people will never use grits at the top or bottom of this scale.
It's often thought that the grit number refers to the number of grit particles per square inch. Not so. Rather, the number scale refers to the number of holes per square inch in the screens that are used when sieving the abrasive grains during the sandpaper's manufacture. For example, in 60-grit sandpaper, the abrasive particles used in the paper were sieved through a screen that had 60 holes per square inch.
How Sandpaper Grit Works
Coarser, or lower-number grit, sandpaper removes wood and other materials faster and with less effort than finer sandpaper. It does this by cutting the fibers on the material's surface.
Aggressive scratching is desired when you want to remove much material or to create a rounded edge, or to remove old paint or blemishes. But the coarse sandpaper also leaves deep scratches.
At the other end of the spectrum, very fine sandpaper removes a tiny amount of material, with the effect of smoothing the surface. The finer the paper, the smoother the surface. The concern here is that if you switch to a fine paper too soon, you'll spend a lot of time sanding to get the results you want.
Also, sanding wood with too-fine paper, or sanding too much, can actually burnish or create a shine to the surface. This produces overworked areas that can hinder the absorption of stains and other finishes. Excessively sanded wood can create a blotchy appearance when stained and finished.
The trick, then, is to start with the highest grit (coarsest sandpaper) that will meet your needs relatively quickly, then move up to progressively higher grits (smoother papers) as the surface gets closer to the finished product—and to stop when it's smooth enough for your liking.
Sandpaper Grit Ranges
While you can find many differently graded sandpapers available, most sanding projects call for papers in the following grit ranges:
#60–#80 Grit: Coarse
Sandpaper grit in these low numbers cuts through the old paint and rough edges with ease. It can also take off enough wood to shape and round edges.
Coarse-grit sandpaper is not recommended for fine details or for edges and corners that you want to keep sharp. Also, be very careful using this on veneer plywood since the thin face layers are easy to sand through.
#100–#150 Grit: Medium
The most often-used gauge of sandpaper grit is in the medium range. For most applications, it is hard to go wrong with sandpaper grits in this range. You can work down difficult materials by applying more pressure to your workpiece. Or, you can preserve fine materials by letting up on the pressure. This grit is generally used for bare wood surfaces.
A final sanding with 150-grit paper is commonly recommended for wood surfaces that will be painted; it leaves a little texture, or tooth, to the wood surface for the paint to grip onto.
For whatever type of projects you work on, it is always beneficial to have medium-grit sandpaper on hand.
#180–#220 Grit: Fine
Seldom used on the first run-through, unless the surface is already smooth to the touch, fine-grit sandpaper in this range is typically for second or third sandings. Sometimes, fine-grit sandpaper is used to roughen glossy paint in preparation for applying another coat. Bare wood that will be stained usually should not be sanded with higher than 220-grit paper. Fine or ultra-fine sandpaper grits are used for furniture work.
#320 Grit: Ultra-Fine
Ultra-fine sandpaper grit is used to achieve another level of smoothness on all types of materials. With wood, ultra-fine grits usually are reserved for smoothing painted surfaces between coats. Many finer grits are used for wet sanding, which creates a fine, gritty slurry that complements the sandpaper's efforts at smoothing. #320 grit sandpaper is even used as one of the first grits when sanding down solid surface countertops.