Brushes for Applying a Finish
In addition to using the right brush and the correct technique, practice counts as well – lots of it. Like most things in life, repetition builds skill. You don’t expect to cut perfect dovetails the first time round, nor should you expect to achieve a perfect finish without practicing your brushing technique.
Most of my finishing is done with shellac or varnish. Occasionally I’ll use a waterborne finish for light-coloured woods when I want a super clear finish with minimal amber or yellow tone. All these film finishes are tough, wear well, have good abrasion and water resistance, and can be rubbed to produce an exceptionally even, smooth surface.
Surface preparation is an important factor in getting a good finish. You want to select the right abrasive to get the smoothest surface. Similarly, when it comes to brushing on a finish, you want to use the right brush. The most important part of a brush is its filaments (also referred to as “bristles” or “hairs”). It’s the filaments, along with your brushing technique, that will have the greatest impact on the quality of your finish. With proper care, brushes will last for years, so save yourself a lot of frustration by using quality brushes right from the start and keeping the brushes in top condition. The shape of the brush tip is also important. Avoid brushes that are trimmed flush across the end. A chisel tip will give you much better performance. Cheap brushes will invariably result in inferior-looking finishes.
When the tips of the filaments are split they are said to have 'flagged ends'. This allows for more even flow out of the finishing material on the wood, and causes less brush strokes.
It can be very handy to have brushes of different widths to use on different sizes of surfaces. Brushes over 2" wide are great for coating large areas, whereas smaller brushes work best for narrower and smaller parts.
Chisel Edged Brushes
A good quality brush isn't cut off square, but tapered slightly toward the leading and trail faces. This allows for a smoother, more even application of finish on wood.
Though not nearly as a nice to work with as a good quality brush, disposable brushes can be thrown away when you're done with them. They can be used for rougher tasks around the shop, or for jobs that don't require a beautiful finish.
Types of brushes
Basically, there are three kinds of filaments used in brushes: natural – made from hog bristle or from ox or badger hair; synthetic – made from polyester or nylon; and natural/synthetic blends. The general consensus is to choose natural brushes for shellac and varnish, and synthetic for waterborne finishes. However, I’ve had good success using natural/synthetic brushes and synthetic brushes with shellac and varnish when I thin the finish by 10 to 20 percent with its solvent. The material used for the brush handle (wood or plastic) is less important than how it feels in your hand. For more controlled brushing, a handle length of 5″ to 6″ works well.
Natural brushes work well on shellac and varnish because they carry more finish than synthetic brushes, so you can lay on more finish with each brush stroke, and maintain a wet edge as you work. When buying a natural brush, look for filaments that have flagged ends – a split at the end of each individual filament. The flagged ends enable the brush to hold more finish and release it with minimal brush marks.
There are two general types of natural brushes. The most common are made from the hair of hogs, typically referred to as “bristle” or “China bristle”. If a brush is labelled “bristle” then it’s made of hog hair. Hog hairs have naturally split ends. They also taper from the base to the tip, which makes the hair strong yet gives it a lot of spring, so that it maintains its shape in use.
Higher-quality natural brushes are made from ox or badger hair, which is a softer, finer, and more pliable filament than ox bristle. You pay a premium for ox or badger brushes, but they can leave a finish that is as good as it gets.
With any natural brush you’ll want to remove any dust or loose filaments before you first use the brush. Shake it out vigorously, then dip it about half of its length into the appropriate solvent for the finish you’ll be using, and then gently tap it against the side of the container.
For waterborne finishes use synthetic brushes, because the water in the finish will cause natural filaments to swell and lose their stiffness. Most synthetic brushes have polyester or nylon filaments, or some combination of the two. Neither is as absorbent as natural filaments, which means you have to load up the brush more frequently. Most manufacturers whip the filaments to split the ends into flagged ends to give a smoother finish. Chinex is a brand name for a synthetic brush with flagged tips, while Taklon is another brand name for brushes with very fine filaments, meant to mimic badger hair.
For large surfaces use a 2″ to 4″-wide brush, while for smaller panels, frames, edge work and legs, choose a narrower 1″ to 1-1/2″ brush. It’s true that an angled (or “sash”) brush allows finer control in corners and tight spaces, but rather than adding yet another brush to my kit I simply switch to a narrower brush, which I find works just as well.
If you typically work with small items, then pick up a couple of small artist brushes (available with both natural and synthetic filaments). They excel at working in tight spaces, and the super-fine filaments allow the finish to flow onto the work easily with virtually no visible marks.
Vary the load
When applying a finish, think about scale. A large surface can absorb finish at a faster rate than a smaller surface or narrow trim work. Using a heavier load on the larger surface makes it easier to maintain a wet edge. Conversely, applying too much finish to a carved or contoured piece will result in runs and sags that can be difficult to correct. With practice, and paying attention to the feel of the brush as you apply the finish, you’ll learn to identify the correct load for each situation.
When loading the brush, you only need to dip the bottom third or half of the brush into the finish, and then wait for the finish to wick into the brush. Before moving the brush to the project, adjust the amount of the load by lightly pressing the brush against the side of the container.
Rather than brushing from one end of a panel to the other end, begin by placing the brush a couple of inches from the end of the panel and move the brush to one end in a continuous smooth stroke. After completing that stroke, return to the starting point and brush back to the opposite end. As you get to either end of the panel the brush should just glide off the top without moving down the edge of the panel. After completing the first pass, go back and use the tip of the brush to gently work the finish across the edge.
Keep brushes clean
Brush cleaning doesn’t have to be arduous or time consuming. If you’re applying a finish over a day or two, then don’t bother cleaning the brush. Instead, suspend it in a container of the solvent for the finish – just make sure the tip doesn’t stand on the base of the container or it will curl up. Before using it again, lightly press the excess solvent out of the brush on the side of the container.
To clean a brush used for varnish or water-based, you want to rinse the brush several times in the solvent for the finish you’re using (mineral spirits for varnish, water for water-based). I do this three or four times and then wash the brush several times with warm water and dish soap. For a varnish brush, rinse the brush first with a citrus-based cleaner and then again with water to remove the final traces of solvent from the brush.
Shake out any excess moisture by swinging it up and down several times, and then wrap the filaments with a piece of paper – you can use strips from paper grocery bags. This allows the bristles to dry and keeps dust from getting into the filaments.
My brush kit
My particular brush kit consists of two brushes for each type of finish. For shellac I use a 2″-wide ox-hair and a 3/4″ synthetic; for varnish, a 2″ and a 1″ bristle brush; and for waterborne finishes a 2″ and a 3/4″ synthetic. The type of woodworking you do will obviously affect your choice of brush.
Buy good brushes, practice applying the finishes you intend to use, take the time to clean the brushes after use, and you’re three quarters of the way to a perfect finish. The last quarter comes from experience.