Polyurethane is a tough synthetic resin, a type of plastic that protects wood surfaces from moisture and general wear and tear. It is available as a clear finish or in a range of sheen options. Polyurethane has replaced shellac and varnish as one of the most popular forms of wood finishes. Which to choose depends on aesthetics, durability, ease of application and environmental concerns.Source:polyurethaneroofcoating.co.uk
There are two main types of polyurethane — water-based and oil based. Both offer a range of sheen options and protect wood from moisture, but each has its pros and cons.
Enhancing Durability: The Benefits of Polyurethane Plywood Coating
Water-based: Looks milky in the can, but dries crystal clear. This is good for light-colored woods and stains where ambering would be undesirable. It is also faster drying and lower in VOCs than oil-based polys and cleans up easily with soap and water. It tends to yellow slightly over time, though.
Oil-based: This offers better durability and a richer color but is more toxic and takes longer to dry. It is best for high-wear surfaces, such as floors, and can be used over other coatings like lacquer. It can also be used on bare wood, but it won’t hold up to heat or chemicals. It tends to yellow slightly over time, but it cleans up with mineral spirits.
Both types of urethane can be applied with a natural bristle brush, foam brush or rag (if using the wipe-on variety). It’s important to apply a thin coat and sand between each coat for a smooth surface.