I just finished my first real woodworking project. During finishing, I noticed the warnings of spontaneous combustion on my cans of stain and poly topcoat. The warnings got to me, and I checked my garage every few hours to make sure my house wasn’t burning down. Is this a real threat? Should I be worried? How should I throw out used rags?
Chris Marshall: Finishes that contain solvents or oil are potential fire hazards. But, the warning about spontaneous combustion actually concerns how you treat your rags that get soaked with finish. What you DON’T want to do is leave varnish-soaked or oily rags wadded up when they’re still wet. As the finishes cure, they absorb oxygen and generate heat. If the finish gets hot enough in a crumpled rag, it can catch fire—and yes, it really happens. The simplest way to stay safe is to spread your rags out flat where they won’t be disturbed until they fully cure and get hard. Then you can toss them in the trash.