Difference Between Spar Urethane and Polyurethane

Woods become vital things in our daily life. Wood polishing is a requirement before it comes to use. Many brands are available in the market that is used for polishing and producing the finished product. There spar urethane and polyurethane are used as primary elements. Though they have similar names, they are different in their properties. Before using, knowing the materials used in it will make you choose right.

Spar Urethane Versus Polyurethane

The main difference between spar urethane and polyurethane is their usage on wood. The spar urethane is applied to the woods that is exposed to sunlight. The polyurethane is applied to blemish the products. They both are used to give finishing to the products like boats to give resistance. The spar urethane must get dilute before use. The polyurethane proffers a glossy look to the wood but is less flexible due to less oil content. The polyurethane gets darken with time but, it is not flammable.

Spar Urethane vs Polyurethane

The spar urethane is a finishing product of wood. It coats in spars or boats and other water-resistant materials. The resin to solvents is high in the ratio, which gives the ultimate protection from wind and sunlight. Both the spar urethane and polyurethane extracts from the oils and modified by chemicals. Like polyurethane, it doesn’t gets darken with time. It is dry as fast and hard in warm conditions.

Polyurethane is also a finishing product that gives a blemish look. It is often mixed with pain to give a shiny look. It is a mixture of polymer and organic carbonate. It is a combination of monomers instead of distinct compounds. Polyurethane is a wide range of components like flexible foams, varnishes, spandex, and electrical potting.

Comparison Table Between Spar Urethane and Polyurethane

Parameters of comparisonSpar UrethanePolyurethane
DefinitionSpar Urethane coats to provide resistance.Polyurethane coats provide a blemish look to the products.
Raw materialMineral spiritsPolymer and carbonate
PropertiesFlexible and malleableRigid and ideal.
Oil ratioGreater in measureSmall compare to spar urethane
Friendly natureMore than polyurethaneLess than spar urethane
PriceSpar urethane is expensive.Polyurethane is less cost comparatively Spar Urethane.

What is Spar Urethane?

Spar Urethane is a wood finishing product. Min wax Helmsman is a famous brand producing spar urethane. It reduces the fades created by UV rays. It is called UV blockers. The spar urethane offers a layer around the product to protect it from rain and sun. Since it extracts from oils, it makes us easy to apply. The urethane formulated self-leveling and gets dried fast. It is suitable for all weather conditions. It takes 4 to 6 hours to dry and needs 8 hours for recoating. Minimum two coats need to look polished.

Before applying to any products, it is vital to clean the surfaces, and the outsides must be free of wax, grease, and lacquer. Add 10% of spar urethane with bleach and water to use. The dust-free surface will shine more. Using wax stripper, remove wax from surfaces. If you are using filler or putty, then it must be wax-free. While applying spar urethane, the temperature must be 13-32 Celsius with humidity below 85%. It has a flashpoint of 41 degree Celsius. Wooster Angle paintbrush treats as the best for applying spar urethane.

Oil modified is the resign type with mineral spirits as solvents. Mostly it comes with a warranty of 3 years. The mixing ratio is 1:3:1 to activate the base. It gives 1.0-2.0 mils of thickness after the first coat. It is vital to choose a bristle brush to make a great look. Discoloration may happen due to over-white or light paints. Apply the second coat after the first feels hard. It takes three days to make the product to normal usage.

What is Polyurethane?

Polyurethane coats give a shiny look to the product. It is first invented by Otto Bayer, a German, in 1937. The reaction of di and tri isocyanates is polyurethane. It contains two types of monomers. By reacting di-isocyanates with polyols in the presence of a catalyst, Polyurethane produces. The increased interest in greens makes use of polyols that derives from vegetable oils. It extracts from soya seed, neem seed, castor. To use polyurethane as a flame retardant, it combines with phosphorus.

The catalyst in polyurethane divides into two- Basic and acidic amine. Polyurethane polymers are available in both foams and non-foams. Using the surfactants, the characteristics of polyurethane gets determined. By mixing two liquid streams, polyurethane get produced. Polyol contains a catalyst and blowing agents that base called polyurethane system. The fluorinated polyols get assembled by copolymerizing the chlorotrifluoroethylene and tetrafluoroethylene.

When polyurethane exposes to fire, it releases carbon, hydrogen, and nitrogen oxides. Polyurethane made with aromatic isocyanates has chromophores that react with light. It results in discoloration over time. Heavy UV rays may affect the foam structure that causes yellowing in the outer layer. The physical properties get changed due to heavy exposure to ultraviolet rays. Hydrolysis is a process when polyurethane reacts to the air. The enzymes like esterase, urethanase, hydrolase, and protease, cause microbial degradation in polyurethane.

Main Differences Between Spar Urethane and Poly Urethane

  1. Spar Urethane contain Mineral spirits, and polyurethane contain Polymer and carbonate.
  2. Spar Urethane is Flexible and malleable, and polyurethane is rigid and ideal.
  3. Spar Urethane has a high oil quantity, and polyurethane has a low oil content.
  4. Spar Urethane is more friendlier, and Polyurethane is less friendly.
  5. Spar urethane is expensive, and Polyurethane is less costly compared to Spar Urethane.


Fine finish quality is vital for good products. Both Spar Urethane and Polyurethane provide a great look to the products. Spar Urethane provides a malleable and classy look to the products. Polyurethane gives a shiny and bright look to the products. Both have high resistance to alcohol and chemicals. Keep ventilated area to apply the Spar Urethane and Polyurethane.


  1. https://www.mdpi.com/386084
  2. https://link.springer.com/chapter/10.1007/978-94-011-6940-0_11
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