Q: I recently read an item about adding something to polyurethane to make it cure faster. It was published in the December 2002 issue of Woodworker’s Journal in your Finishing Thoughts column. I went back through my issues and that one is missing. Can you help?
A: I just checked my copy, and it says nothing of the sort. Nor have I ever recommended adding anything to polyurethane to speed the cure. Here’s what I have said, both in that article and in others.
First, waterbased polyurethane dries much faster than oil based. Bear in mind that how fast it dries and how fast it cures are two different things; both take about three to four weeks to fully cure.
I also said that if you were planning to spray oil based polyurethane, reduce it with acetone, which evaporates faster than mineral spirits. Fast solvent makes it easier to spray without drips and allows what amount you do spray to cling. However, it does not change either the real drying time or the cure time of the finish. Because drying time is based on how thickly it is applied, thinner coats will in fact dry (and cure) faster than thicker coats. That’s not a chemical change; merely a physical one.
This is not to say that there are not chemicals which will speed the cure of polyurethanes, but I do not and have not recommended them, and for good reason. They require more knowledge about the original formulation, as well as more experience in formulating finishes, than most finishers possess. Without that knowledge, you can create a disaster in the race for speed.
Michael Dresdner
straight talk about wood finishing
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