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Polyurethane finish for wood furniture.

Polyurethane coating.

Polyurethane is one of the chemical that is very popular and has been known by many people today. There are many human needs goods are made from polyurethane. According to its name, the polyurethane is a polymer formed from the urethane polymerization reaction.
The urethane is a material produced from the reaction between the hydroxyl with poly isocyanate. There are many materials containing hydroxyl group such as: alkyd, castor oil, urea, acrylic, cellulose, polyester and many others. Due to the large hydroxyl group, there are many types of polyurethane. In the finishing industry there are many type of polyurethane paints are available which each has his unique characters.
In the furniture finishing there are many types of polyurethane finish that is sometimes confusing for people who deal with. In the furniture finishing industry, at least there are three polyurethane finishes: two component polyurethane, polyurethane oil and polyurethane water based. 

 Water based polyurethane.
The water based coatings are widely used in wood finishing is usually made of 1 component urethane, modified acrylic or acrylic. The water based coating that is made from urethane sometime is called as water based polyurethane. The water based coating made of urethane usually will produce a stronger finishing layer compared with the other water based materials. This coating is one component clear coating that will be dry without any hardener in the mix. This paint can be applied by spray or brush with satisfactory results. Yet after all this paint is a water based paints that could not generate a strong finishing layer as a polyurethane two components. This finish is also cannot produce looked and performance as the two component polyurethane.
Polyurethane oil.  
Polyurethane oil is a kind of oil finish made from a urethane resin component. This paint can be applied with a wipe, dyed or brushed as well as other oil finish. Urethane oil will soak into the wood and reacts with the wood to make the wood become harder and durable. This finishing material can not produce a layer of thick films. The finish generated will look very natural and show the beauty of wood grains and pores. Like other oil finish, this material cannot make any film built and provide protection for the wood underneath.

The two component polyurethane.
This is the type of polyurethane that most well known as the PU coating. This PU is clear coating that can produce strong and thick layer of film. The resulting film will be very strong, high resistance to scratches, heat and solvents. It consists of paint and a hardener that is packed separately. The paint and hardener should be mixed with a certain ratio when it  applied on. Polyurethane paint which is already mixed with the hardener wills immediately react, dry,  hardened and can not be redissolved. The time to dry after the paint is mixed with his hardener is called pot life. The pot life of Polyurethane is relatively short, about 1 - 2 hours. You can find more information in our previous article: Polyurethane coating.

Polyurethane finish

Polyurethane finish is finishing system which is using polyurethane clear coating to form his film layer. Polyurethane system finishing is relatively more difficult than the NC finishing system. Polyurethane finish has relatively long drying time. A layer of polyurethane clear coating needs about 1-3 hours to dry and be able to be sanded. Some types of PU clear coating even requires longer time to dry. 
The PU finish needs to use the same clear coating types from beginning to end. If we want to combine the PU clear coating with other finish then we have to make sure  that the overall system is compatible. The stain and glaze used for PU finish should be chosen which is suitable with the PU clear coating. The PU finishing stain for solid color such as: base coat, enamel or toner stain should be the PU type.

Polyurethane finish is more widely used to coat the finish on the goods which require strong and thick film layer. Furniture for hotels, cafes, bars or items such as dinning tables are very suitable to be finish with PU system. The PU finishing is usually used for relatively clean finish. Antique finishes that require a lot of works is very rarely done in the PU finish because it will require very long execution time. The clean finishing like: contemporary or classic finish with a thick film layer is the kind of finishing that is suitable for PU finish.

The things that are need be considered at PU finish.   
  •  PU clear coating requires a long drying time, so the PU finish usually needs long processing time.
  • PU clear coating after it reacts and dry can not be washed and removed thinner. Therefore, if there are any mistake in the process then it will be very difficult to be revised. After the polyurethane is dry completely it cannot be resolve with any solvent, The only way to revise is by strip the layer with paint remover chemical, which it is a big job. Touch ups that can be done quite ease in lacquer finish will be very difficult to do on the PU finish.
  •  Polyurethane coating has long time to get dust free dry. Since that it is very sensitive to the presence of dust and dirt at the drying process. The application and the drying of the PU clear coating especially for top coat should be done in the clean and dust free room.
  •  Polyurethane is also very sensitive to the humidity. The drying process that occurs in high humidity will be very vulnerable to the occurrence of blushing. And if the blushing occurs on its film layer, it is need to be re sanded and re-coated to get fixed.
  • The PU hardener is easily become damaged. PU Hardener is an isocyanate which is very sensitive to environmental especially with the air humidity. The hardener that is placed in the open air will soon hardened and can not be used anymore. To keep it stay longer it should stored in closed cans.

2 comments for "Polyurethane finish for wood furniture."

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