In the same way surface preparation is key to getting a great paint job, sanding is the task that, when completed properly, transforms your woodworking project into something truly special. Yet, for many people new to woodwork, sanding is something that gets rushed, overlooked, or done very badly.
In this article, I’ll run through the things you should understand about sanding that will help you achieve a pleasing finish to take your woodwork to the next level. I suggest you get the feel of sanding by hand as it’s not only therapeutic, it helps you learn the basics of woodworking and allows you to pick up a few tips and tricks before you advance to using powered sanding tools.
So what is sanding, and how does it work?
While our topic today is sanding wood, the principle of sanding remains the same whether the base material we are sanding is wood, metal, stone, glass, or plastics. Sanding describes the process of removing material from a surface by mechanical means. We use sanding for various reasons, including:
- To roughen up a surface to ensure a sufficient grip when gluing
- To remove a layer of material such as paint or glue
- To smooth a surface for aesthetic reasons and surface finishing
- To reduce the size of an object for fit-up purposes
While reasons one and three may appear to be opposites, the roughness or smoothness that occurs after sanding is due entirely to the size of the cutting edges used to remove the material. Let’s talk about that.
Sandpaper, grit, and grit sizes
Sandpaper consists of a backing material, abrasive grit, and a bonding medium that holds the grit to the backing. The backing is normally paper, cotton, or polyester for the sandpaper we use, although rubber, mylar, and rayon are also used. The material used for the grit can take many forms, but common grits are aluminum oxide, garnet, emery, or silicon carbide. You’ll often hear sandpaper, such as aluminum oxide sandpaper, referred to by the grit material.
Sandpaper is classified by the grit size used. The number you see on sandpaper is inversely proportional to the grit particle size. Woodworking sandpaper showing a grit of 30, or 36, is very coarse sandpaper often used in the early stages of sanding a hardwood floor. 80-grit sandpaper is medium-coarse and often used to remove paint or varnish or in the early stages of sanding wood in preparation for finishing.
100 to 120-grit sandpaper is classed as fine, and you can use it to prepare wood for finishing, sanding plaster, or removing stains from a wooden surface. When you reach 150 through to 220-grit sandpaper, you’re in a very fine territory that is used for final wood finishing or scuff sanding between coats of paint or polyurethane.
The bonding medium used to hold the grit to the backing is usually the old-fashioned hide glue or a form of resin. You may have heard of wet-and-dry sandpaper, which uses a resin bond and a waterproof backing that allows the paper to be used with water. wet-and-dry sandpaper works best when wet as the water stops the spaces between the grit from clogging with removed material.
The point to remember about abrasives of any kind is that they work by scratching the surface and removing material. The finer the sandpaper, the less visible the scratches, and the smoother the surface appears. However, you’ll see the scratches if you view the surface through a suitable magnifying glass.
What is a sanding block, and should I use one?
A standard sanding block is a block of wood or cork with flat and parallel sides. You wrap the sandpaper around the block and hold it in place with your hand as you sand a surface. If you wish to maintain a flat surface on wood while using sandpaper, you should use a sanding block.
You’ll see people using sandpaper with their hands, which has its place when sanding surfaces that are shaped or have compound curves. However, if you try to use just your hand on a flat surface, your hand will follow contours and bumps, and due to the uneven pressure, you’ll not get a flat surface by the time you finish.
What’s the best sanding technique?
There are several tips to remember when sanding that will give you better results:
Tip #1: Sand with, or along, the grain of the wood
When you sand along, or with, the wood grain, the grain pattern helps to disguise the scratches made by the sandpaper grit. When you sand across the grain or at right angles, you are drawing attention to the scratches, and the finish will look unsightly. Once you sand across the grain, the marks can be hard to remove.
Tip #2: Work from coarse to fine as you sand
When you start sanding, you often want to remove material quickly at first. You can use medium-grit sandpaper such as 80-grit to start, then move up to finer sandpaper as you see the finish you want. There is no need to select the next finest paper; you can skip a grade or two. For instance, I may start with 80-grit, move to 120, then 180, and finally 220 or 240 if I want an exceptionally fine finish.
Tip #3: Use a light pressure
Too often, people lean on the sanding block, believing it’ll remove material more quickly. While it may initially, it may also mark the surface of your work and clog the sandpaper. All cutting tools work best if you let the edge do the cutting while you guide them, using light pressure. You’ll also retain better control of the sanding block and feel less tired at the end of the day. If the sandpaper gets worn, replace it. Don’t just press harder.
Tip #4: There is such a thing as sanding too fine
When applying stain to wood, the finer you sand, the less stain the wood will take up. Some claim that sanding too fine will block the wood pores; others that the smaller scratches retain less stain. Whatever your personal beliefs on the issue, there is no doubt that sanding wood to a very fine finish will result in the wood taking less stain. You can use this in your favor if you want a milder tint and a fine finish. The effect is almost invisible when moving from the 100-grit range to the 200-grit range. But jump to 400-grit, and you’ll see a marked difference.
For a review of the points we’ve just discussed, here’s a quick video by the Family Handyman:
Sanding wood to stain
When sanding wood you wish to stain, I’d start at 80-grit sandpaper and sand in the direction of the grain until I have a consistent finish on the wood surface. Then vacuum up the sawdust and lightly wet the surface of the wood with a damp rag. If you intend to use a water-based stain, use water on the rag; if the stain is oil-based, use mineral spirits. This wetting will show up any marks that may remain on the surface. Continue sanding until all marks are gone, occasionally rechecking with the damp rag method.
Begin sanding with higher grit sandpaper, regularly vacuuming up the sawdust as you move to a finer grit. You might jump to 100, then 120, and finally 180-grit. You can continue into the higher grits of 200, 300, or 400 if you wish, but remember the caution about how much stain a finely sanded surface will take up. Finally, use a vacuum and a painter’s tack rag (or the damp rag once again) to remove any last dust and debris on the surface before applying the stain.
Sanding wood to paint
When you intend to paint wood, the sanding process gets a little easier, as you’ll be covering the surface with an opaque film, hiding any small scratches. You’re also better off leaving some scratches on the surface as the scratches give the paint something to adhere to. I wouldn’t go any finer than 180-grit when sanding a surface to accept paint.
Once again, clean any sawdust from the surface and surrounding area well. You wouldn’t be the first person to have a gust of wind or air movement from a passing person lift sawdust from surrounding surfaces and deposit it on your wet paint. Remember to lightly scuff the paint surface with sandpaper between each coat once dry. You’re not looking to sand off what you’ve just put on; you just need to create that keying surface to aid adhesion. Don’t sand the top coat.
Using Power Tools To Sand
We’ve spoken of hand sanding, yet there comes a time when your job is large, or the thought of hand sanding a particularly rough piece makes you want to go and lie down. In that case, you can turn to an electric sander. Let’s understand some common types of electric sanders you’ll come across.
An orbital sander consists of a motor and a square or rectangular sanding pad made of steel and covered with rubber. The sanding pad will have clips to hold the sandpaper, and you normally cut the sandpaper size to fit the sanding pad from a full-size sheet, which is why these sanders can also be known as sheet sanders. This sander is called an orbital sander because of how the sandpaper moves in small circular movements or orbits when operating.
Orbital sanders are known as finishing sanders, as they normally do the final few grit sizes once the wood has been rough sanded using a belt sander.
A disc sander can be as simple as a sanding pad driven by an electric hand drill or a purpose-built item. Use a disc sander slightly tilted so that one side of the circular pad does the sanding. Be sure to secure your workpiece, as the disc sander can move or even throw smaller pieces of wood, and maintain a firm grip as it can have a mind of its own if you lose concentration. You use this form of sander for the initial rough sanding of large surfaces, and it’s very maneuverable, allowing you to get into places other sanders might struggle while allowing you to sand wood with curves.
A belt sander has a motor driving a sandpaper belt tensioned between two rollers. Between the rollers is a flat pad across which the sandpaper passes, and it is this pad that you place on the wood to remove material. The belt is tensioned by a spring-loaded quick-release lever that allows belt replacement. There is also a knob you can adjust to ensure the belt tracks in a straight line when rotating.
You use belt sanders for roughing down and flattening large areas of wood. Their size can make them cumbersome, and the more powerful models can be tiring to use for extended periods. Be careful with a belt sander as it can mark surfaces if used with too much force, not kept moving, or not kept level.
A palm sander is another form of finishing sander, and it normally has a square or circular pad that moves in the same way as an orbital sander. Its distinguishing feature is its size, lightweight, and low power. A palm sander is made to be used one-handed, so it is easy to control and achieves particularly smooth finishes. Not the sander to use if you want to remove lots of material.
Random Orbital Sander
The random orbital sander is a cross between a disc sander and an orbital sander, with a random action that spins and makes circular orbits. The sander is held fully down on the wood, unlike a disc sander, and the random action ensures the sander does not leave any sanding patterns or marks on the wood, which some of the other sanders can do. This sander is a good all-rounder as it can do rough material removal and fine finishing work.
Using An Electric Sander
Each sander variety has its idiosyncrasies, so take some time to understand how your particular model works before launching into your masterpiece. Do try it on scrap wood first! Powered sanders have damaged many fine pieces of work because they were inappropriately used.
- Be sure to wear a dust mask when using a powered sander, as they throw a lot of fine sawdust, even when used with a vacuum attachment.
- With all powered sanders, keep them moving on the wood to maintain an even material removal. Pause too long with a disc sander or a belt sander, and you’ll end up with dark scorch marks which are difficult to remove.
- Beware the edge of the belt or disc, as you can mark and damage vertical timber if you’re trying to get into a corner.
- Wear gloves. A powered sander is a great skin removal tool.
Sanding wood is not difficult, and doing it by hand is immensely satisfying while providing a lovely finish to your work. It gets you close to your work and focuses you down so you’ll see every imperfection and mark, which is more than you’ll get from using power tools. I hope this article has helped, and good luck with your project.