How to Correctly Apply Varnish with a Brush
Wood varnish is one of the best finishes available to the small shop woodworker who doesn’t own wood finishing spray equipment. It’s easy to apply, attractive, and very tough. It provides a much faster build than wipe-ons and results in a thicker, more protective coat.
Unfortunately, many woodworkers shy away from brushing varnish, frustrated by runs, drips, and other imperfections. But take heart; there’s no magic to creating a beautiful brushed varnish finish. You simply need to understand a few basic principles and techniques, which I’ll share with you here.
For this article, I have varnished a mahogany TV riser stand (designed to straddle a DVD player). I chose to use oil-based varnish, applying it with a natural bristle brush. However, the same basic approach works for water-based varnishes, except that you’ll need to work somewhat faster and use a synthetic brush. If you’re new to varnish, I suggest starting with a relatively small project to get the feel of the material and process.
Selecting a Finishing brush
For oil-based varnishes, use a natural-bristle brush such as china bristle (hog’s hair), or a synthetic (commonly nylon/polyester) brush with flagged bristle tips.
For water-based varnishes, use only synthetic bristles, as water causes natural bristles to splay. For general work, use a chisel-edge brush (Photo A). A sash brush works better for getting into corners and detailed areas. Avoid square-edged brushes for varnishing.
Avoid inexpensive brushes, which won’t spread varnish well and may leave stray bristles imbedded in the finish. A good quality brush that’s well cleaned and cared for will last you a very long time. A 2" brush can run as high as $80; expect to pay at least $25.
China bristles are good for oil-based varnishes, while the flagged-tip synthetic bristles on the sash brush work for both oil-based and water-based varnishes.
Preparing to Finish Your Finish
Your shop environment and workpiece preparation are just as important as the application of the finish. Varnish applies and dries best in temperatures between 65° and 80°, with only moderate humidity. Cold impedes timely drying, and heat can accelerate it before the varnish has a chance to level properly.
Set up good reflective workshop light or work near a window that banks the light off the workpiece toward your eyes. Also, prepare appropriate work supports. I use triangular sticks or boards with screws driven fully through with the screw tips offering workpiece support.
Sand the work through 220 grit, and brush away the dust or blow it off outside with a strong blast of compressed air. Then wipe off the work with a tack cloth (Photo B). Clean your finishing area, let any ambient dust settle, and don dust-free clothes before starting work.
TIP ALERT: One thing worse than dust settling into a wet finish is a bug. Make sure your shop is impervious to flying critters while varnishing.
Plan How You'll Apply Your Finish
Plan and rehearse your finishing sequence to allow handling of a piece in process and to ensure that the most visual surfaces (usually the top and front) are left for last to ensure maximum attention. In general, begin with the interior or bottom of a project, orienting the surface at hand horizontally whenever possible to allow the finish to level out. Then move to the less evident exterior surfaces, such as the sides of a cabinet. Work discrete sections one at a time, such as a panel face. Leave the top surface of a project for last to ensure the best leveling as the unit sits and dries.
In the case of complex surfaces such as frame-and-panel assemblies, brush the interior edges of the frame first, moving outward to the flat areas. There are no hard and fast rules to finishing sequence. Just calculate the approach as best you can for each project.
Cardinal Rules for Brushing Finish
- Don’t overload the brush.
- To minimize drips and runs, never brush inward toward a corner or edge.
- Always “tip off” surfaces after completely coating them.
Apply the First Coat of Finish
Stir varnish well; never shake it. Shaking can introduce bubbles, so why invite trouble? Pour the amount you think you’ll need for the first coat into a separate, clean container to avoid contaminating the source can with dust. With oil-based varnish, I thin the first coat with 10-50% mineral spirits for better penetration and ease of application, testing the altered viscosity on a sample board. You want it thin enough to flow well from the brush, but thick enough to resist sagging and running. Some water-based varnishes don’t tolerate thinning; check the product label.
Before varnishing, prime the brush bristles by immersing them in either mineral spirits (for oil-based products) or water, and then shake off the excess. Priming conditions the bristles for work and eases brush cleanup.
Dip the brush into the varnish, loading it with an amount appropriate to the surface at hand. For example, to prevent runs and drips, just dip the tip when brushing edges. When coating broad surfaces, load enough for efficient transfer without dipping the bristles more than half of their length. Avoid dragging the bristles on the rim of the container, which encourages bubbles. Instead, press them against the side of the container to remove excess finish.
I usually begin with the edges because any spillover is easily cleaned up afterward. When varnishing an edge, orient the project with the less evident face downward, and angle the brush slightly so that one of its chiseled edges is doing the work. First brush outward toward a nearby corner, and then in the opposite direction to the other corner (Photo C)
After the edge is completely coated, follow up by “tipping off,” as explained in the 'Tipping Off' Tip. My next step is a bit unorthodox, but it works well as long as the faces of the panel are not yet varnished: Wrap a clean rag tightly around your finger, and lightly drag it along the underside of the edge to thoroughly wipe away drips (Photo D). If the faces are already finished, use a very lightly loaded brush to spread out any runs.
Learning How to Tip Off When Applying Varnish
Varnish needs to be preened after application to spread out any runs or pools before the finish starts to set up. The trick is to “tip off” the wet varnish by lightly dragging the tips of unloaded bristles over it while holding the brush at a steep angle. Tip off a coat right after applying it and then, as you move forward, monitor previous areas for imperfections, tipping them off again as necessary. Never drag the brush against edges or corners, and stop tipping off when the finish starts offering resistance and retaining brush marks.
To varnish broad surfaces, begin at one edge of the panel, and work in a series of wide, continuous, overlapping swaths. Starting a few inches in from one end, pull the brush smoothly across the wood (Photo E).
Next, working backward from your previous starting point, complete the swath by moving in the opposite direction (Photo F). Move slowly enough to allow the finish to flow from the bristles, but quickly enough to avoid puddles. As you progress, gradually increase the bristle angle to encourage the finish to flow out. As you complete the swath, pull the brush straight off the end of the panel to prevent the bristles from crawling down the edge. Apply each subsequent swath of varnish in the same manner, slightly overlapping the previous one.
As you work across the width of the panel, occasionally tip off the previous areas. As you near the opposite edge, load the brush less to allow it to absorb varnish from the tipped-off areas. If necessary to properly tip off of the final area, lighten the brush load by dragging the bristles across clean scrap wood.
How to Fix Varnish Drips & Sags
In spite of careful work, some dripping and sagging are inevitable. Fix these areas after the coat of varnish has dried, removing drips by slicing them away with a very sharp chisel as shown in the photo at DIR. Sags can be scraped away with a fresh single-edged razor blade.
Applying Subsequent Coats of Varnish
Rubbing Varnish to Create the Perfect Sheen
Give the final finish at least a few days to cure fully before rubbing it out to the desired sheen. (If the finish clogs the sandpaper, it needs more curing time.) I typically wet-sand using 400-grit wet/dry paper, lubricating the surface with mineral spirits or water to remove any dust nibs or rough areas. After wiping it dry, I aggressively scrub the surface with 0000 dry steel wool to even out the sheen and remove any gloss speckles remaining in pores and other low lying areas (Photo H). Follow up with a coat of wax.
