Working with Polyurethane

A short jaunt to Lowe’s yesterday to get stuff to make shelves turned into an all day adventure, but I have to say I enjoyed myself. (And made it out of Lowe’s with only one new power tool, a cheapo Black & Decker finishing sander.) I am just using pine boards for the shelves, although I tried to sand them down at least somewhat—getting the ends to shed the crags and ridges from being sawed ended up being too much trouble—but I wanted to put a coat of some sort of sealant on them since at least one set of these shelves will be in the bathroom. (And the other will be used in the kitchen, so you can be sure it’ll get at least a few splashes of mysterious kitchen goo.)

I ended up getting a can of polyurethane, which wasn’t what I had originally grabbed. The first stuff had a two-hour cure; the polyurethane suggests six to twelve. So while it was curing outside, passing insects and leaves drawn irresistibly to the sticky surface, it ended up getting rained on. No big whoop in the end—it had set up enough to repel water, although I’m going to have to re-sand the backside where it soaked up some newspaper ink.

Anyway, my question is this: From my cursory reading of the can, it appears polyurethane can cause rags to burst into flame. This is disturbing. I had to throw away my first brush when it hardened, as I didn’t have any mineral spirits around to clean it with. How much of a practical danger is this? Is it only when the polyurethane is still liquid? The Cabot web site doesn’t have much information about it at all.

My hopes for a smooth, shiny surface are pretty much gone, and with it comes a bit of relief. Now I just want to make sure that my cheap pine boards are somewhat moisture resistant while not setting my apartment on fire while I try to figure out how to dispose of my supplies responsibly. I’m not going to do it, but I kind of get why people just pour paint down the bathtub drain. It’s a really easy consideration.