If your library is made of wood, then we recommend using a standard house paint (water-based or oil-based paints will both work fine). They’re durable, inexpensive, and available at any hardware or home goods store. Before you paint, start by applying a coat of primer. Primer is designed to bond well with wood. Then, apply a few coats of paint on top of the primer. No coats of varnish or sealant are needed if you’re using house paint. (The only time we recommend using varnish is if you painted your library with acrylic paints that aren’t designed for outdoor use.) You could choose to stain your library instead, but it won’t last as long as paint will.