by David J. Marks
Step 1: Brush or spray shellac on the area to be filled. You can use off the shelf shellac by BIN Zinsseer . The Universal Sealer that BIN sells is 100% wax free. If you use their spray cans, warm them first by placing it next to a light bulb until the can feels warm to the touch. This will help it flow better. Make sure the area you are working in is around 75 degrees with low humidity.
If you are brushing, thin the shellac with alcohol to the consistency of water (equivalent to a one pound cut) and brush it inside the gap to seal any end grain. This will prevent the dye from seeping into the end grain and causing discoloration.
Step 2: After the shellac has dried, I like to use masking tape to further prevent any pigment getting into the grain and causing discoloration. Sometimes I will tear the masking tape and use the ragged edge to follow the irregular shape better.
Step 3: Epoxy Fill: epoxy is typically a 50/50 mix, except with some brands. To color it, I like to make some sawdust by sanding a piece of wood with 220 grit sandpaper using a power sander and some newspaper underneath to catch the dust. It is always best to use a piece of wood that matches the wood you are trying to fill. When a situation calls for black, I have relied on tinting colors. I have been using Mixol , also available at Woodcraft or Rockler. Mixol makes pigments that are very concentrated. The black is called Schwarz (German for black). I like to just put a drop or two into the epoxy, stir it up, and then hold it up to the light to see if the color is transparent or opaque. If it is transparent, then I add a couple more drops. I keep doing this until the color is opaque. The goal is to apply the minimal amount of liquid pigment until you reach an opaque color. If you apply too much of the liquid pigment, then you will soften the epoxy.
Whenever possible, use slow setting epoxy (30 minutes or longer) to minimize any air bubbles. In a pinch, 5 minute epoxy works fine for small gaps. In terms of brand, I have been in the habit of ordering System 3 from Woodcraft and I also have had good success with the epoxies that Tap plastic sells. To tell the truth, I am not sure if I see much difference when I use the epoxies that Ace Hardware sells as well. You know the old expression….”any port in a storm!”
Step 4: Using a narrow stick, I drip and spatulate the epoxy into the gap. Resist the temptation to level it, because the epoxy will slowly shrink and it is better to leave a puddle on the surface so that when it has cured, it will be level flush with the surface.
Step 5: After the epoxy has hardened (you won’t be able to dent it with a screwdriver) it is time to level it. I prefer to use a scraper. If your skills are not good with scrapers, then you could use a belt sander to level the epoxy ( or buy my DVD on Sharpening Scrapers). As you get close to the masking tape, you can use a putty knife to lift and remove any remaining masking tape. Any tiny pin holes can be filled with clear CA glue (cyanoacrylate glue). CA glue is available in thin, medium, and thick. You can also purchase a spray catalyst. Spray the catalyst on first, wait a minute, and then drip in some CA glue. Luthier’s Mercantile in Windsor, Calif., Woodcraft, and Rockler, all sell CA glue as well as little plastic pipettes. These are great for applying CA glue with better control.
Step 6: Sanding. After everything is nicely filled, then comes the step we all love most: MEDITATION. Sometimes this is wrongly perceived as a laborious task, often referred to as the dreaded sanding. So use whatever method you prefer to do an attitude adjustment and begin the process of sanding. Power sanding is OK, but I always like to finish with hand sanding using a block to level everything. Remember, if you got to start with 80 grit, that is OK. If you are scraping, you should be able to start sanding at 120 grit or hopefully at 180 grit. The rule of thumb is to take out the worst stuff with whatever low grit sandpaper is necessary and then work your way up in increments of 50 percent. For example, if you start at 120 grit, divide that by 50%, which equals 60; add that to the 120 and you have 180 grit. I always like to sand to a minimum of 320 grit. Higher is better. If you take it to 600 grit, the grain and figure in your work will have great clarity.