The imperfections of reclaimed barn boards are part of their charm. However, because they've been sitting outside for years, you'll need to clean them before putting them to use. When shopping for barnwood, ask whether it has been kiln-dried and the nails have been removed. Dried boards will help reduce moisture issues. The drying process also kills any insects hiding in the wood—you don't want any unwelcome surprises when you bring the boards home! And if the boards still have nails, you'll have to tear them out yourself, which can be a time-consuming job. It's also wise to sand the edges of the boards so they won't be splintery.
Once you have dry, nail-free, sanded boards, use a bristle brush to scrape off dirt and dust. You can also use a vacuum to pick up debris. If needed, an air compressor can help get rid of any remaining grime. Aim to use as little water as possible when cleaning barnwood as too much water can alter the appearance of or damage aged wood. Let the boards dry fully after any application of water.
When the barnwood is all cleaned up, seal it with a water-based clear coat to protect your shelves from wear and tear. Test the sealer in an inconspicuous spot first, such as the underside of the shelf boards, to make sure it doesn't change the surface to an undesired color. Let dry completely.