Polyurethane, Shellac, Varnish and Lacquer – Use a cotton swab with acetone on it and apply to the wood. If it becomes tacky, than it is shellac or varnish and if it beads, it has a polyurethane finish.
Step 2: Lacquer Thinner or Acetone
After a few minutes, shellacs and traditional varnishes will become tacky. These will typically bead up on urethane finishes, however, lacquer thinner may make some water based urethanes tacky. Further testing can differentiate the two.
Cut out a long piece of the material and pull it apart. If it is polyurethane, a great amount of force is needed to pull apart the material and break it. If it is a silicone, it will stretch a great distance without exerting too much force. It will also stretch back and forth rather easily.
Unlike polyurethane, varnish is designed for outdoor projects and is not typically used for indoor surfaces such as a hardwood floor. While polyurethane is water- or oil-based plastic resin, varnish is older and made from resins, oils, and solvents.
Water-based polyurethane is clear and will remain clear overtime, while oil- based polyurethane generally has a yellow tint to it that intensifies the color of the wood overtime. Another consideration when determining which base is best suited to your needs, is what you need the finished surface for.
Make sure to sand the polyurethane between coats.
Polyurethane is a category of wood finish products that are either water- or solvent-based clear coatings that can range from a gloss finish to a satin finish. Under most circumstances, a varnish product can be applied over a polyurethane coating.
Appearance. Water-Based Polyurethane: Dries clear without adding color to the wood, preserving the natural look. It is often preferred for lighter woods and for applications where the natural color of the wood is desired.
Polyurethane is more durable and protect against scratches. Water-based polyurethanes dry very quickly and have a low toxicity level, making these products ideal for DIYers who don't want to deal with safety equipment or be left vulnerable to bad weather if working outside.
Polyurethane (/ˌpɒliˈjʊərəˌθeɪn, -jʊəˈrɛθeɪn/; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links.
COLOR: Oil based poly has an amber hue, whereas water based poly is clear. An oil based polyurethane will continue to amber and darken over time, while water based poly will remain clear for the lifetime of the hardwood floor.
Always sand the polyurethane before painting. If you don't invest time in sanding, your paint over polyurethane project won't be a success. Although these how-to painting steps are for kitchen cabinets, they also can be applied to wood floors, doors, or furniture that have a polyurethane finish on them.
Varnish is a clear transparent hard protective coating or film. It is not to be confused with wood stain. It usually has a yellowish shade due to the manufacturing process and materials used, but it may also be pigmented as desired. It is sold commercially in various shades.
The easiest option is to apply a clear, water-based finish such as Minwax's Polycrylic.
Gloss Levels for Polyurethane
High-gloss: High-gloss finishes are very shiny and reflective. They enhance the wood's grain and color but show scratches and imperfections more readily. Semi-gloss: Semi-gloss finishes have a slightly less reflective surface, offering a good balance between shine and practicality.
If you do decide to go ahead and apply new varnish over the top of old varnish, make sure that the existing varnish is scratch-free and do give the old varnish a light sanding using 120-grit sandpaper and wiping away any dust. This will ensure that the new varnish has something to bond to.
While it is similar to varnish in terms of application and appearance, polyurethane is generally harder and more abuse resistant, which means it is commonly used for sealing wood floors. It's less flexible than varnish, so it may not be the best choice to use on wood pieces that move or flex.
Waterborne polyurethanes usually require a minimum of 3-4 coats to be effective. Although there is some evidence that too many coats can result in a plastic-like finish, waterborne polyesters are thinner than other types and therefore require several more coats to provide the same protection for hardwood floors.
Simply place a few drops of water on the wood surface and wait for a couple of minutes. If the water beads up, the wood likely has a finish, such as varnish or polyurethane.
Polyurethane, Shellac, Varnish and Lacquer – Use a cotton swab with acetone on it and apply to the wood. If it becomes tacky, than it is shellac or varnish and if it beads, it has a polyurethane finish. If it is lacquer, the lacquer will dissolve completely.
Polyurethanes. The most popular surface finishes are oil-based and water-based polyurethanes. Water-based polyurethane, which can be applied relatively easily, dries quickly (12 hours), has low odor and low volatile organic compound (VOC) emission, and maintains a clear, smooth, shiny finish.