Feb 19, 2020 Spray polyurethane with a paint sprayer rather than applying with a paintbrush for a quick, easy, professional looking finish on DIY furniture projects. Polyurethane provides a clear, durable layer of protection for DIY furniture. It can also be used for floors, doors, woodwork around windows and doors, and cabinets. Nov 22, 2021 Before applying polyurethane to the floor, clean it properly, and after each coat, sand the surface of the wood. Yellowing Problem Yellowish color taking over the main color is a common thing in using oil-based polyurethane.