Sanding is one of the most critical steps in the process of building any woodworking project and if not done properly can lead to disappointing results. Just think of all the time and money invested in building a woodworking project, to have it turn out badly because you did not do the sanding properly. With a little insight and the right materials a poorly sanded project will be a something you will never have to deal with again. We will go over some of the basics of sanding and the different types of sand paper and what they are used for.
The term sandpaper is from years ago when sand and dust from bricks were used to finish wood surfaces. It has become a generic term because sand is no longer used in the production of sandpaper. It has been replaced with a number of different abrasives. The sand that used to be used has been replaced with modern materials that do a better job. We now have glass-paper, aluminum oxide, silicone carbide, garnet paper and steel wool all of which are used for different applications.
Glass or flint paper as it is known is made from crushed quartz and is the least expensive of all sandpaper. It is best used for removal of heavy paint and resinous materials, because it is so inexpensive once it loads up you can throw it away and put on a new sheet. This type of sandpaper should not be used for finish sanding, because it tends to leave fine dust in the grain of the wood which may have a reaction to certain finishes. This type of sandpaper usually comes in an off-white color.
Aluminum Oxide is the most common and readily available of all abrasives and is the preferred sandpaper for most machine sanding operations. Aluminum oxide is made from bauxite fused in an electric furnace. It comes in a number of different colors red, brown, gray or black. This type of sandpaper is effective on wood but can also be used to sand and polish iron and steel. Aluminum Oxide last longer than both glass and garnet sandpaper.
Garnet sandpaper is probably the most used sandpaper in any woodworking shop because it leaves extremely smooth surfaces. It is the sharpest of all the abrasives although not the hardest. The abrasive in Garnet sandpaper is constantly breaking exposing new sharp edges which is the reason it leaves such a smooth surface. The color of garnet sandpaper is normally red.
Silicon Carbide is the most expensive of all abrasives because it is a synthetic material which is almost as hard as diamonds. It is available in ultra fine grades and is used in finish sanding of paint, varnishes and urethane
All sandpaper comes with either a paper or cloth backing. Paper backing comes in five different grades A through F with F being the heaviest. Lighter papers are used for finer grit abrasives. There are two grades of paper backing X and J, X being the stiffest and used for heavy-duty machine standing, belt sanders for example. Paper backings rated J are much more flexible and are used in hand standing where you have to get into contoured areas.
Sandpaper also comes with either an open or closed coat. Closed coat sandpaper is basically a sandpaper that is 100% covered with abrasive and are best used for hand sanding. Open coat sandpaper only has between 50% to 70% of the paper backing covered with abrasive. Open areas allow for the dust to fall out and leads to less load up. Open coat sandpapers are used with machine sanders and work well with dust collectors.
Sandpaper comes in different grit sizes, determining grit size is a very simple process. Let’s say you have 120 grit sandpaper, the abrasive is run through a sieve that has 120 openings per linear inch. The same is true for all different grit sizes. Grit sizes are as follows 40-60=course, 80-100=medium course, 120-150=medium, 180-220=fine, 240-up=very fine.
That pretty much covers all the basic characteristics of sandpaper. Now let’s discuss the proper use of sandpaper so you get the best possible results. Most woodworkers truly dislike this part of completing a woodworking project, because it is the most time-consuming part of any woodworking project. However, this is the part of the project that determines whether a finished product is something you will be proud of or something that will end up in the scrap heap.
Always sand with the grain to get the smoothest possible finish, and use the proper sandpaper for the job you are doing. Start with a coarser grit and work your way to a finer grit. When hand sanding use a block with a felt pad. (here is a great woodwork hint, a blackboard eraser works just great) It is always helpful when hand sanding to count your strokes, it leads to a more uniform finish. Another great woodworking hint is to use an old nylon stocking, running it across the surface will help find rough spots that you might not feel with your bare hand.
When using a power sander let the abrasive do the work excessive pressure is unproductive. As with hand sanding move with the grain of the wood. Never start the sander when it is on the sanding surface and always keep the sander moving to prevent gouges. You should always use a tack cloth between sanding operations. A tack cloth is a sticky cloth that can be purchased at any paint store. It picks up all the tiny dust particles on the sanding surface. You should always use a very fine grit sandpaper between each coat of finish, then wipe it with your tack cloth before applying the next coat of finish.
Armed with this knowledge your woodworking projects will turn out to be something you will be extremely proud to have in your home.