Letter: Catalyzed Polyester Finish

by Mike Doolin

Originally published in American Lutherie #85, 2006

I’ve switched from waterborne finish to catalyzed polyester. Why? Hardness and speed. Poly provides the durability to which most steel-string players are accustomed. It’s basically 100% solids and cures by catalysis instead of evaporation, so it doesn’t shrink over time. I can rub out a finish after five days cure, and a year later it will look just as good.

But those qualities come at the price of toxicity and flammability. I now have a commercial spray booth with an explosion-proof room around it, and a supplied-air full-face respirator. With solvents like acetone and MEK and with MEKP as the catalyst, this stuff is not to be trifled with. Besides, it stinks to high heaven until it’s cured. I still recommend waterborne finishes, particularly KTM-9, to small-production and hobbyist luthiers and anyone unwilling or unable to make this kind of investment in finishing equipment. ◆