Acrylic lacquers were developed to eliminate the yellowing  problems and crazing of the nitrocellulose lacquers. General  Motors started using acrylic lacquer in the mid-1950s, and  they used it into the 1960s on some of their premium model  cars. Acrylics have the same working properties but dry to a  less brittle and more flexible film than nitrocellulose lacquer.  Lacquer is one of the easiest paints to spray, because it dries  quickly and can be applied in thin coats. However, lacquer  is not very durable; bird droppings, acid rain, and gasoline  spills actually eat down into the paint. It still has limited use  on collector and show automobiles because they are usually  kept in a garage, protected from the environment.  The current use of lacquer for an exterior coating on an  aircraft is almost nonexistent because of durability and  environmental concerns. Upwards of 85 percent of the  volatile organic compounds (VOCs) in the spray gun ends  up in the atmosphere, and some states have banned its use.  There are some newly developed lacquers that use a catalyst,  but they are used mostly in the woodworking and furniture  industry. They have the ease of application of nitrocellulose  lacquer with much better water, chemical, and abrasion  resistance. Additionally, catalyzed lacquers cure chemically,  not solely through the evaporation of solvents, so there is  a reduction of VOCs released into the atmosphere. It is  activated when the catalyst is added to the base mixture.  Polyurethane is at the top of the list when compared to  other coatings for abrasion-, stain-, and chemical-resistant  properties. Polyurethane was the coating that introduced  the wet look. It has a high degree of natural resistance to the  damaging effects of UV rays from the sun. Polyurethane is  usually the first choice for coating and finishing the corporate  and commercial aircraft in today’s aviation environment. The term urethane applies to certain types of binders used  for paints and clear coatings. (A binder is the component that  holds the pigment together in a tough, continuous film and  provides film integrity and adhesion.) Typically, urethane is  a two-part coating that consists of a base and catalyst that,  when mixed, produces a durable, high-gloss finish that is  abrasion- and chemical-resistant.  Acrylic simply means plastic. It dries to a harder surface but  is not as resistant to harsh chemicals as polyurethane. Most  acrylic urethanes need additional UV inhibitors added when  subject to the UV rays of the sun. There are several methods of applying aircraft finish. Among  the most common are dipping, brushing, and spraying. The application of finishes by dipping is generally confined  to factories or large repair stations. The process consists of  dipping the part to be finished in a tank filled with the finishing  material. Primer coats are frequently applied in this manner. Brushing has long been a satisfactory method of applying  finishes to all types of surfaces. Brushing is generally used for  small repair work and on surfaces where it is not practicable  to spray paint.  The material to be applied should be thinned to the proper  consistency for brushing. A material that is too thick has a  tendency to pull or rope under the brush. If the materials  are too thin, they are likely to run or not cover the surface  adequately. Proper thinning and substrate temperature allows  the finish to flow-out and eliminates the brush marks. Spraying is the preferred method for a quality finish.  Spraying is used to cover large surfaces with a uniform  layer of material, which results in the most cost effective  method of application. All spray systems have several basic  similarities. There must be an adequate source of compressed  air, a reservoir or feed tank to hold a supply of the finishing  material, and a device for controlling the combination of the  air and finishing material ejected in an atomized cloud or  spray against the surface to be coated. A self-contained, pressurized spray can of paint meets the  above requirements and satisfactory results can be obtained  painting components and small areas of touchup. However,  the aviation coating materials available in cans is limited, and  this chapter addresses the application of mixed components  through a spray gun.  There are two main types of spray equipment. A spray gun  with an integral paint container is adequate for use when  painting small areas. When large areas are painted, pressure- feed equipment is more desirable since a large supply of  finishing material can be applied without the interruption  of having to stop and refill a paint container. An added  bonus is the lighter overall weight of the spray gun and  the flexibility of spraying in any direction with a constant  pressure to the gun. Methods of Applying Finish Dipping Brushing Polyurethane Spraying Urethane Coating Acrylic Urethanes 8-5