Michael Dresdner

straight talk about wood finishing

Q: How do you prevent bubbles in spar varnish? I have tried bristle brushes, sponge brushes, and even putty knives.
A: In real estate the adage is location, location, location. With brushing oil based varnish, it’s technique, technique, technique.
A few basics come first. Start with the softest natural bristle brush you can find; ox hair is ideal, but ox hair blends, which are more available, will also work well. Stir the varnish, pour some out into a square pan, and reduce it at least 15% with mineral spirits. Soak the brush up to the ferrule in mineral spirits before you begin; then squeeze out the excess, and dip only the last one third of the bristles into the varnish. Touch the tips of the bristles to the flat side of your square pan; this will leave the brush loaded, but not dripping.
Touch the tips down gently at 45 degree angle and gently press to deflect the bristles as you start to move. This will cause the finish to rise to the top of the bristles; the area you see looking down onto the brush. The object is to then gently slide the brush out from under the finish.
You will notice I said gently more than once. Brushing is a calm, Zen activity. Focus, think about letting the fluid flow, and whatever you do, don’t scrub with the brush.
There’s more, but it really requires a photo essay, and I can’t do that here in this blog. However, I have done it in several books and in a DVD, if you’d rather see it in action than in a series of still photos. You’ll find very good brush work teaching, including how to clean and preserve brushes, and even how to buy brushes, on pages 25 – 31 and 128 – 131 of The New Wood Finishing book, and on pages 63 – 69 in Wood Finishing Fixes. Page 67 of that book, which is a Q&A format, begins “How do I eliminate bubbles in brushed finishes?” You can find both the books and DVD in the books and videos section of this blog.


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