Urethane and polyurethane are coated on many of the things we use every day. Although these terms are used interchangeably, there are very noticeable differences between the two. The most obvious difference is that polyurethane contains many different urethane compounds. However, there is a lot more things to compare and contrast in the battle between urethane vs. polyurethane.
What is Urethane?
Created in the 1950s-1960s, urethane contains R1-O-(CO) NR2-R3, which are both amides and esters of carbonic acid. This flexible and malleable crystalline compound can be molded into various shapes and sizes and can be used for many different purposes. However, they are mostly used in insecticides, veterinary medicines, and human pharmacotherapy. Although they are generally non-toxic to humans, they can be toxic and cause cancer in small animals especially when taken orally. Urethane doesn’t have a specific smell but it does taste bitter. In fact, the intake of medicine with urethane content can actually cause nausea in some people. When used in paints, urethane is better than polyurethane in the following areas:
- More resistant to scratches & dings
- Not as harmful to the environment
- More durable & stable
It also has load bearing and compression properties, a good friction coefficient, and it can maintain a product’s shape and size for a very long time. It can be painted over enamel and is also very durable. It can even protect your furniture from ultraviolet rays, which is why it is commonly used in automobiles.Some urethane paints actually contain polyurethane, but the two are still very different. Urethane paints are very resilient, so it can be hard to make them stick to surfaces or paintbrushes. Because of this, special urethane brushes were developed. When using urethane paint it’s important to sand the surface vigorously before starting. There are two ways to apply urethane paint: dilute the paint and apply multiple thin layers or apply a thick coat and “tip” using a near-dry paintbrush.
Spar urethane is a type of urethane that is carried in water. It is made for outdoor use and doesn’t yellow as much as other types of varnish. In fact, it is one of the best choices to use if your furniture is going to be exposed to a lot of water because it is water-resistant. However, it’s not the best choice for furniture that is going to be moved often. Expansion and contraction with the wood is made easy because of urethane’s softness and pliability. To get the best results, use mineral spirits to thin the urethane up to 40%. It’s likely to dent after a few uses, but it definitely works better than other kinds of finishes for outdoor use.
What is Polyurethane?
Like spar urethane, polyurethane is a plastic resin that is carried in water. As its name suggests, it is made up of more than one urethane compound, which are joined together by a reaction known as polymerization. There are many different types of polyurethane, but most of the newer blends are non-toxic.
For more information about the toxicity of polyurethane please refer to this post: Water Based vs. Oil Based Polyurethane
Because polyurethane is stiff and hard, they are mostly used in solid materials such as foot wears, foams, etc. Some paints also contain them in order to have better coating and shine. Polyurethane finishes can either be satin or gloss. Ordinary polyurethane takes around 8 hours to dry, which means that the surface will be susceptible to dust and other small particles in the air. Because of this, water-based polyurethane was made for faster drying. Polyurethane bonds well with both metal and plastic, and it’s very resistant to the environment’s harshness and oxidation levels. It is also very stable against hydrocarbon solvents. Although polyurethanes are harder and have better wear tendencies than urethanes, they are usually used for indoor furniture and products instead of outdoor ones.They are the better choice for firmer items and they are very advantageous over rubber or even steel. They also have better compressive loading than urethanes and have better aging properties than others. For a long lasting coat, polyurethanes are usually mixed in paints.
Polyurethane is not easy to apply perfectly. If applied the wrong way, the finished product may show some bubbles and brush strokes. This is because the solution is very thick. In order to avoid these imperfections, it is important to use the right brush and to thin the solution to up to 50% with mineral spirits. Thinning helps the finish become more level and can help you avoid brush marks. However, this will require you to apply more layers of the finish on the surface. Other ways of avoiding bubbles and brush strokes on your furniture include using sponge brushes or sprays. These, however, do not give the same results as brushing with regular brushes.
Applying polyurethane with brushes may be the best method, but it is not the easiest. One way of applying the solution easily is through the wiping method. This method is actually very easy and beginner-friendly in the sense that you simply wipe thinned varnish on your furniture’s surface. This method ensures that your furniture will have no bubbles or brush strokes, but you will need to apply more coats in order to get your desired thickness. Furthermore, because the solution is thinned, it will take less time to dry so there is a lower chance of dust and other particles to stick to the surface. Both urethane and polyurethane can be found in things that we use every day. These terms are often confused with each other and sometimes used interchangeably. However, they aren’t at all the same. There are many differences between urethane vs. polyurethane. It is important to know all of these so you know the better choice for your furniture refinishing project.