Sealers and their use are a source of confusion to many woodworkers, but they needn't be. In truth, the first coat of any finish will act as a sealer, penetrating the wood fibers and leaving a rough surface for subsequent coats to bond to. But clear finishes vary in how effective they are as sealers, and products sold as "sanding sealers" often are not the best solution, either. Read on to find out when to seal, what products work best with what finishes, special products for special uses, and why often your best choice can be summed up in one word: shellac.

From Fine Woodworking #227