Sanding sealers, also known as first-coat sealers, are recommended when refinishing furniture. Although it’s a good step to take regardless of the type of stain you’re using, a sanding sealer is especially necessary when using water-based stains. Apply it after you’ve bleached your furniture, but before staining. A sanding sealer provides an important barrier to keep the wood pitch and stain from bleeding into the water-based topcoat. It also helps fill small pits and pores present in hardwoods such as oak, ash, mahogany and teak, and it helps you attain a smooth, level surface. This is especially important on tabletops, dressers and bureaus.