Teak sealer is often recommended to preserve the natural honey color or to darken the color of the wood. Teak sealer contains UV protection to keep the sun from graying the furniture as well as a fungicide to prevent the growth of mold and mildew on the surface of your furniture. Teak sealers can be applied to new teak or old teak furniture after it has been cleaned. Sealer is not the same as varnish. It is meant to preserve the color of the wood and is breathable, letting the natural oils escape without bubbling or peeling like varnish. Sealers and preservatives serve both as protectants and stains. Generally, the darker the stain, the more sun protection it provides, and the less often it needs to be reapplied. For furniture with an ageing varnish that is peeling, cracking or bubbling, it is recommended that you sand this finish off and use a teak sealer or just let the teak stay bare.