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Expert's Corner — oxidize

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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