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Winter 2013-2014

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AW Extra 7/11/13 - Brush-On Finish the Easy Way

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Brush-On Finish the Easy Way

Thinning the poly is the secret.

By S. Lloyd Natof


Finishing is a challenge—right? It’s one thing to get a nice finish on a small, flat sample board, but good luck with those inside corners, vertical surfaces, curved areas, thin edges, and framed panels. I don’t care for spraying, which comes with its own set of problems, so I’ve developed a technique to apply a finish by hand, using only a brush and some rags.

The general sequence of steps goes like this: First, I apply a coat or two of thinned-out polyurethane. Then I scuff sand the finish. Finally, I apply a coat of gel varnish to remove the sanding haze. The goal is a finish that appears level and clear, shows the pores and texture of the wood, and feels very smooth.

Applying a finish by hand has many attributes in common with using hand tools. The process is quiet, meditative, and benefits from a methodical approach.

 

Materials

• Brush. I use a 3" foam brush with a wood handle. I cut about 1" off the end of the handle so the brush can be stored in a quart can of finish. This eliminates the use of solvents to clean the brush.

• Polyurethane. I use semi-gloss Minwax Fast Drying Polyurethane for the interior of a cabinet and gloss for the outside.

• Thinner. I use naphtha rather than paint thinner because it evaporates faster. The goal is to thin the poly so that it will stay wet and flow out better without extending the drying period too much.

• Gel varnish. I like Bartley Gel Varnish.

• Sandpaper. I use 3M 216U Fre-Cut Gold stearated sandpaper in P400, P600 and P800 grits.

• Felt block. This is for backing the sandpaper.

• Cotton rags or paper wipes. I use Brawny medium weight Taskmate Wipers, avaliable at the grocery store.

• Japan drier. This helps speed the drying process. It’s available at most paint stores.

 

Technique

I completely pre-finish all the interior surfaces and partially finish the exterior surfaces of a cabinet before assembly. Pre-finishing lets you work on surfaces without having to brush into an inside corner. Pre-finishing also allows you to place all your parts in a horizontal position to prevent drips and runs (Photo 1). You’ll finish one surface at a time, letting it dry completely before turning it over to finish the opposite side. Before finishing, tape off mortises, tenons and all glue surfaces with standard masking tape. Trim the tape after it is applied using a utility knife.

Start by sanding everything to 180 grit. Wet the sanded surfaces with a damp rag or sponge. After the wood dries, scuff sand the raised grain using a felt block and 220-grit paper. Wipe off or vacuum the dust. The surface doesn’t have to be absolutely dust-free because scuff sanding between coats will smooth out any vagrant dust in the finish. You won’t have to bother with a tack rag.

Next, prepare the finish. Stir 1/3 capful of Japan drier into one quart of poly. Thin the poly with naphtha until it is more like water than syrup (usually about 40% naphtha by volume). The exact amount of thinner is not that important. What you want is a coat that flows out and stays wet while you brush.

Apply the poly using a disposable foam brush. After you’re done with each coat, store the brush in a partial can of varnish. One brush will last for all the coats you’ll apply.

Working with a foam brush requires some getting used to. The main issues are that it unloads quickly and pushes a small puddle of finish in front of itself. With practice, you will get a sense for the right amount of finish to load into the brush. As for the puddle, let me show you how I finish a large panel.

Start by applying a perimeter of finish roughly 1" from the edge (Photo 2). Then, work the finish back and forth to fill in the middle (Photo 3). To avoid pushing the puddle over the edge of a panel, be sure to keep shy of the edges. Next, work the dry border with a brush that’s loaded just enough to wet the wood but not enough to drip over the edge (Photo 4). Go back over the entire surface, in any direction, to move the finish around and create a thin even film with no puddles or dry patches. Finally, brush with the grain using very light strokes at a low angle, like a plane landing (Photo 5). Start the strokes just in from the edge and continue all the way off the opposite end. The only downward pressure should be from the weight of the brush; you are just lightly smoothing the finish in the direction of the grain and don’t want to push finish over the edge.

When you’re done, examine the panel in a raking light. You should see a wet and even coat of finish. The brush marks should start to flow out and disappear, while the perimeter begins to look drier. If you see puddles or dry spots, move the finish around with the brush. Follow this up with light strokes that go with the grain. Check for drips on the edges and wipe them off.

Next, tackle the edges. Brush on the poly and wipe it off right away with a cloth (Photo 6). This leaves a thin film of varnish that won’t sag or drip. It’s enough protection for edges that won’t be handled very often. Use a raking light to check for a ridge of finish that may have been pushed onto the top. If you see one, smooth it out with a light brush stroke following the grain.

If you want to have more finish on an edge, wait until the faces are dry, then stand the part up on edge for brushing. Don’t forget to wipe off any drips after brushing the edges.

If you’re finishing a curved part, use a much drier brush (Photo 7). Dip the brush’s tip in the finish and stroke lightly with the brush held in a vertical position. Limit your working area to one face and brush out a thin, even coat. Wipe off the adjacent faces to remove any drips.

When you’re done brushing, clean the can’s rim, drop in the brush, hold a deep breath for a minute, and exhale into the can. Quickly put on the lid. This helps to replace the oxygen in the can with carbon dioxide, which minimizes the skin that may develop on the finish’s surface.

Lightly scuff sand every surface after it has dried for one day (Photo 8). Be careful near the edges, where the finish can be extra-thin. The edges that you wiped off should already be smooth, but if you need to sand out a little fuzz, use a very light touch with 800-grit paper.

Once you’re done sanding, use a new foam brush to apply 2-3 coats of gel varnish to the interior surfaces only (Photo 9). Working one part at a time, brush the gel on most of the surface, then smear it around and begin to remove it with a wipe in each hand. Switch to a new set of wipes to remove all the excess gel varnish (Photo 10). Any remaining gel will dry to a sticky mess, so get it off now. Use a clean, folded wipe on the edges. Remove any vagrant gel from the underside of the part and clean off smudges from your hands on the top.

Now you can remove the tape and glue your project together. Apply two coats of thin gloss poly on the outside surfaces (Photo 11). Sand with 400 grit in between coats. If you’re finishing a cabinet, brush one side at a time, rotating the case to bring a new side horizontal after the previous side has dried. You should be able to finish two or three sides in one day. Blankets and padding are important to protect the sides from damage as you rotate the cabinet. Wipe off any drips that may form on the edges (Photo 12).

Note: The used wipes should be spread out to dry when you are done.

Wait at least two days for the second coat to dry. Then lightly scuff sand with 600-grit paper to dull the glossy surface by about one-third (Photo 13). Repeat with 800-grit paper wrapped around the felt block. This time, push down harder to level the surface (Photo 14). Look for a 90% sanded surface with an even pattern of small, shiny pores after you wipe off the dust.

Finally, use a gel varnish to reduce the sanding haze, just as you did with the interior surfaces (Photo 15). I usually apply two to five coats of gel on top of the poly to get the finish I am looking for. For my really special pieces and on dark finishes, I polish with 3M’s Imperial Hand Glaze #5990 between the last coats of gel. I rarely use wax except on thin or satin finishes.

This finishing process can be used over dyes and stains, but you must be very careful near the edges, especially with dyes. Dark colors require more coats of gel and Hand Glaze polishing to remove the sanding haze.

Click any image to view a larger version.

1. Brushing a finish is much easier before assembly. For the best results, thin the finish, tape the joints, and lay all the pieces flat on your bench.


2. Brushing technique really matters. On a panel, start by brushing a perimeter. Leave a dry border to prevent drips.


3. Fill in the perimeter. Lay out an even, wet coat of polyurethane over the whole surface, except the border.


4. Brush the dry border, moving parallel to the edge. Hold the brush lightly, barely overhanging the edge.


5. Make the final strokes with an unloaded brush, following the grain.


6. Finish the edges next. Brush on the finish, then wipe it off immediately.


7. Curved surfaces test your skills. Use a less saturated brush with a light touch and check repeatedly for drips or sags.


8. Scuff sand with 400-grit sandpaper after the first coat has dried overnight. Wrap the paper around a felt block.


9. Apply gel varnish to all the interior parts with a foam brush. Gel varnish helps remove the sanding haze.


10. Wipe off all the gel with two rags and two hands. Remove the tape from the joints, then glue and assemble your project.


11. Apply a second coat of poly to the outside of the project.


12. Wipe up any drips that form on the edges with a folded towel.


13. Sand the exterior surfaces with 600-grit paper. Sand to within 1/8" of an edge, then make very light passes in this zone.


14. Repeat the process using 800-grit paper to level the surface. Again, sand much less near the edges.


15. Apply gel varnish until you get the look you’re after.




This story originally appeared in American Woodworker December/January 2009, issue #139.

December/January 2009, issue #139

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