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Expert's Corner — thinner

Wetting to Predict Blotching

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Wetting to Predict Blotching

You can usually get a pretty good idea whether or not the wood you are using will blotch when a stain or finish is applied by wetting the wood.You can use any liquid, but water will raise the grain causing you to have to sand more. Mineral spirits (paint thinner) works well except if you intend to apply a water-based finish. Some residue oiliness may remain and cause the finish to fish eye—that is, bunch up into ridges rather than level out.Denatured alcohol would be better for this situation because it will totally evaporate. But it evaporates quickly, so you...

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TIP: Tung Oil and Varnish Sold as Tung Oil

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Finishing is hard enough even without the mislabeling that is so prevalent on the part of many manufacturers. The mislabeling makes it difficult for us to know what we are buying and using. The accompanying picture shows dried puddles of two commonly available products both labeled “tung oil.” These two products could hardly be more different. The tung oil on the left is real tung oil, the oil produced from pressing the nuts from tung trees, which are native to China. A puddle of the oil dries wrinkled, and it never really hardens. You can always scrape it off with...

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TIP: Thinning Polyurethane with Naphtha

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Naphtha dries (evaporates) much faster than mineral spirits (paint thinner). This leads many to believe that thinning polyurethane with naphtha will make it dry faster. This is not entirely the case. Like all varnishes, oil-based polyurethane dries in two steps. The first is evaporation of the thinner. The second, and much longer step, is by the crosslinking brought about by the introduction of oxygen from the air. When you apply polyurethane, you notice that it stays wet on the surface for a short time as the thinner evaporates. Then the finish goes into a tacky or sticky stage for an...

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Asphaltum, A Forgotten Finishing Gem!

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Many years ago, back when the dinosaurs roamed the earth, I had the privilege of working with two older gentleman in Charleston, South Carolina. Their forte was antique restoration as well as creating reproductions of the same. They went by the names of Jim and Bob, one was from Germany as I think, and the other from Sweden or Italy, I can't recall. The language barrier for whatever reason was not an issue, even though neither spoke very good English. It was simply woodworking seem to create a universal understanding between us.  As close as I could determine they were...

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Using a Viscosity Cup

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Using a Viscosity Cup

Finishes vary in viscosity (thickness in liquid form) depending on their type and formulation, and especially in temperature differences. The viscosity is thicker when the finish is cold and thinner when the finish is warm. To measure viscosity dip a viscosity cup into a finish so the cup is full. Then lift the cup out of the finish and begin timing the drainage with a stopwatch. When the stream breaks, indicating that the cup is empty, stop the timer. The number of seconds is the measure of the viscosity. There are many types of viscosity cups. Some are quite expensive....

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