Article: How To Sand Raw Wood
In this article we will discuss a few of the correct methods used for sanding raw wood when refinishing furniture.
Other than using a stationary sander or a belt sander, which will take a good deal of practice to learn to control, there are three general methods of sanding most wood surfaces: with just your hand backing the sandpaper, with a flat block backing the sandpaper and with a vibrator or random-orbit sander.
Sanding furniture seems simple, right? Well, it is - to a point. As with most things we do in life, there are right ways and wrong way. To take it a step further, there are also hard ways and easy ways. Understanding basic principles, grits, products and techniques will not only save you time and money, but assure a higher quality finished product.
It's rarely beneficial to sand raw wood finer than #180 - 220 grit. This rule does not apply however, to wood that has a finish applied. Unless I am sanding a soft wood, such as Pine, I normally use 100 to 120 grit, and I'll sometimes finish it off with 180-220 grit before staining. The most common grit I use in the Studio for sanding raw wood is #120 grit.
Film-building finishes, such as varnish, shellac, lacquer and water-based finish, create their own surfaces after a couple of coats. The appearance and feel of the finish is all its own and has nothing any longer to do with how fine you sand the wood.
Fine sanding. Sanding finer than #180 or #220 is wasted effort in most cases. In fact, the finer the grit the wood is sanded to, the less color a stain leaves when the excess is wiped off. In this case, the top half was sanded to #180 grit and the bottom half to #600 grit. Then a stain was applied and the excess wiped off.
The finer you sand, the less stain color will be retained on the wood when you wipe off the excess. If this is what you want, then sand to a finer grit. If it isn't, there's no point going past #180 grit. The sanding scratches won't show as long as they are in the direction of the grain.
Sometimes with vibrating and random-orbit sanders, sanding up to #220 grit makes the squiggly marks left by these sanders small enough so they aren't seen under a clear finish. Sanding by hand in the direction of the grain to remove these squigglies then becomes unnecessary.
Squigglies. Random-orbit sanders are more efficient than vibrator sanders, but they still leave cross-grain marks in the wood. I refer to these as squigglies. One way to remove them is to sand them out by hand in the direction of the grain after sanding to the finest grit, usually #180 or #220, with the sander. Doing this is especially important on soft woods, such as pine. On hard woods, you can remove the squigglies simply by finish sanding with a finer 220 grit sandpaper on the orbital.
In all cases when sanding by hand, it's best to sand in the direction of the wood grain when possible. Of course, doing this is seldom possible on turnings and decorative veneer patterns such as sunbursts and marquetry.
Cross-grain. Sanding cross-grain tears the wood fibers so the sanding scratches show up much more, especially under a stain. The best policy is to always sand in the direction of the grain when possible. The scratching that does occur is then more likely to be disguised by the grain of the wood. When sanding with the grain isn't practical, I'll often opt for a scotch brite pad to do my sanding in those areas.
Cross-grain sanding scratches aren't very visible under a clear finish, but they show up very clearly under a stain. If you can't avoid cross-grain sanding, you will have to find a compromise between creating scratches fine enough so they don't show and coarse enough so the stain still darkens the wood adequately. You should practice first on scrap wood to determine where this point is for you. If you find that you have created cross grain scratches, you may want to seal the wood before staining.
Three Sanding Methods:
Other than using a stationary sanding machine or a belt sander, which will take a good deal of practice to learn to control, there are three methods of sanding wood: with just your hand backing the sandpaper, with a flat block backing the sandpaper and with a vibrator or random-orbit sander.
Using your hand to back the sandpaper can lead to hollowing out the softer early-wood grain on most woods. So you shouldn't use your hand to back the sandpaper on flat surfaces such as tops and drawer fronts because the hollowing will stand out in reflected light after a finish is applied.
Hand sanding. The most efficient use of sandpaper when backing it with just your hand is to tear the sheet into thirds cross-ways and then fold one of the thirds into thirds length ways. Flip the thirds to use 100 percent of the paper.
The most efficient use of sandpaper for hand-backed sanding is to tear the 9" x 11" sheet of sandpaper into thirds cross-ways, then fold each of these pieces into thirds length-ways. Sand with the folded sandpaper until it dulls, flip the folded sandpaper over to use the second third, then refold to use the third third. This method reduces waste to zero and also reduces the tendency of the folds to slip as you're sanding.
To get the most efficient use of the sandpaper, fold one of the thirds-of-a-sheet (described above) in half along the long side and hold it in place on the block with your fingers and thumb. When you have used up one side, turn the folded sandpaper and use the other. Then open the sandpaper and wrap it around the block to use the middle.
Most woodworkers use random-orbit sanders because they are very efficient, easy to use, and they leave a less-visible scratch pattern than vibrator sanders due to the randomness of their movement. For both of these sanders, however, there are two critical rules to follow.
First, don't press down on the sander when sanding. Let the sander's weight do the work. Pressing leaves deeper and more obvious squigglies that then have to be sanded out. Simply move the sander slowly over the surface of the wood in some pattern that covers all areas approximately equally.
Second, it's always the best policy to sand out the squigglies by hand after you have progressed to your final sanding grit (for example, #180 or #220), especially if you are applying a stain. Use a flat block to back the sandpaper if you are sanding a flat surface. It's most efficient to use the same grit sandpaper you used for your last machine sanding, but you can use one grit finer if you sand a little longer.
Removing Sanding Dust:
No matter which of the three sanding methods you use, always remove the sanding dust before advancing to the next-finer grit sandpaper. The best tool to use is a vacuum because it is the cleanest. A brush kicks the dust up in the air to dirty your shop and possibly land back on your work during finishing.
Tack rags load up too quickly with the large amount of dust created at the wood level. These sticky rags should be reserved for removing the small amounts of dust after sanding between coats of finish. Compressed air works well if you have a good exhaust system, such as a spray booth, to remove the dust.
It's not necessary to get all the dust out of the pores. You won't see any difference under a finish, or under a stain and finish. Just get the wood clean enough so you can't feel or pick up any dust when wiping your hand over the surface.
How Much to Sand:
The biggest sanding challenge is to know when you have removed all the flaws in the wood and then when you have removed all the scratches from each previous grit so you can move on to the next. Being sure that these flaws and scratches are removed is the reason most of us sand more than we need to.
A lot of knowing when you have sanded enough is learned by experience. But there are two methods you can use as an aid. First, after removing the dust, look at the wood in a low-angle reflected light for example, from a window or a light fixture on a stand. Second, wet the wood then look at it from different angles into a reflected light.
For wetting the wood, use mineral spirits (paint thinner) or denatured alcohol. Avoid mineral spirits if you are going to apply a water-based finish because any oily residue from the thinner might cause the finish to bead up. Denatured alcohol will raise the grain a little, so you'll have to sand it smooth again.
If you are sanding critical flat surfaces by hand, you should always use a flat block to back the sandpaper. If the block is hard (wood, for example), it's best to have some sort of softer material such as cork glued to the bottom to improve the performance of the sandpaper. (I find the rubber sanding blocks, available at home centers, too hard, wasteful of sandpaper and inefficient because of the time involved in changing sandpapers.) I happen to be partial to felt blocks, but they are not easy to find, so the cork glued to a wood block is more practical.
Block sanding. The most efficient use of sandpaper when backing it with a flat sanding block is to tear the sheet into thirds cross-ways and then fold one of the thirds in half. Hold onto the block with your thumb and fingers as shown here. Flip the folded sandpaper for a fresh surface, then open up the sandpaper and wrap it all around the sanding block for a third fresh surface.