Air Bubbles in Her Epoxy
Issue: Issue 93
Posted Date: 2/25/2004
From Women in Woodworking
She'd added colored powder to two-hour epoxy, used it to fill flaws, and found it be very attractive after it was sanded and finished. Her problem, however, were the small air bubbles that appear as she's sanding. She pats, taps, joggles, and thumps the piece after she's applied the epoxy, but usually ends up having to fill in the holes. She wondered if the powder was affecting the mix and the results.
Air bubbles, explained one post, are a fact of life with epoxy. Making sure that the epoxy was warm seemed to help (he suggested setting it next to a heater, and another forum member used a hair dryer as he built up the epoxy), as did going easy on the stirring when mixing. Folding the mixture (akin to folding whipped egg whites) goes a long way toward eliminating air bubbles. Though he often preferred water-based wood filler, another poster explained that he made the mixed epoxy thinner than the instructions call for & using less hardener so the final mix was more like warm honey or thick maple syrup, although that often meant having to fill in some with a second application.
The real solution, insisted a woodworker, was to simply not use epoxy as filler, but stick to wood filler. The latter comes pre-colored and, properly applied, never leaves air bubbles. For a really big hole, start filling with a shim of wood and wood glue (or epoxy if she insists), but switch to wood filler as you get near the surface. One of the earlier prescriptive posters, however, stuck to his guns and had successfully used System 3 and West epoxy for years. By themselves, the two-part formula is only good for small gaps, but the aforementioned manufacturers also offer a variety of fillers (shredded fiberglass, glass beads, and wood flour & a.k.a. sawdust) that beef up the epoxy for larger gaps.
Though not excluding the use of epoxy, another forum member suggested mixing representative sawdust with Elmer's or Titebond to create fresh, homemade wood filler that's sure to match.
Other remedies for air bubbles included:
- Blow on the epoxy & a blast of carbon dioxide helps break down the bubbles naturally created by combining resin and hardener.
- Vibrations are used to get bubbles out of concrete & so set the next project on a running washing machine.
- Hold it under a lightbulb while mixing it, and then add a little fine sifted sawdust until it's the right consistency.
- Squirt a little epoxy on a glass plate (less waste), add a little powder, stir them together with a tongue blade, and then spread it or fill in holes.