Things You'll Need
2-inch foam brush
Clear silicone caulking
Bathroom mirrors are commonly placed above vanity cabinets. Due to their constant exposure to water and moisture, it is important to seal the wood frame and around the mirror properly to prevent water from entering the underside of the mirror. If water somehow penetrates the wood or underside of the mirror, it can cause lifting or damage to the mirror. By properly sealing around a bathroom mirror, you can prevent potential harm to the mirror and drastically prolong the mirror's life.
Tape around the mirror to protect the wall and glass from damage. Apply tape around the entire perimeter of the mirror. If there is a wood frame, apply additional tape to the wall around the exterior perimeter of the frame.
Seal the wood frame with polyurethane using a 2-inch foam brush. Stir the polyurethane with a wooden paint stick, and dab the tip into the sealant. Swiftly brush on a thin layer of polyurethane to the wood frame. Cover the entire surface of the frame. Apply a second coat if needed four to six hours later. Allow polyurethane to dry completely before removing tape.
Remove tape from around the mirror. Remove tape from the wall as well as the surface of the mirror.
Apply a thin layer of clear silicone caulking to the crease between the mirror frame and the wall. Use a wet finger to smooth the caulking over the entire seam. Clear silicone caulking is waterproof, which prevents any water from getting in underneath the mirror.
Remove any excess caulking with a wet paper towel.