have periodic physicals during the time you are working with these coatings. There are two types of polyurethane systems used on naval aircraft-the aliphatic type (used in MIL-C-85285 and TT-P-2756 polyurethane paints) and the aromatic type (used in polyurethane, rain erosion-resistant coatings, MIL-C-85322). These materials present no special hazard to health when cured (dried), but they require special precautions during preparation, application, and curing due to the isocyanate vapors produced. The isocyanates vapors can produce significant irritation to the skin, eyes, and respiratory tract even in very small concentrations. They also may induce allergic sensitization of personnel exposed to their vapors and mists produced during spray applications. Aliphatic polyurethane. MIL-C-85285, is the standard, general-purpose, exterior, protective coating for aircraft surfaces. The polyurethane finish comes in kits that consist of a two-component material resin and a catalyst. The touch-up kits are prethinned and ready for use when they are mixed according to the instructions in the kit. Use aliphatic polyurethane over epoxy polyamide primer and for touch-up and insignia markings over polyurethane paint systems only. Acrylic Lacquer Acrylic lacquer (gloss and camouflage) MIL-L-81352 is the preferred topcoat material for aircraft markings that identify the reporting custodian and for propeller safety stripes. Enamel Finishes Most enamel finishes used on aircraft surfaces are baked finishes that cannot be touched up with the same materials in the field. Minor damage to conventional enamel finishes ordinarily used on engine housings is repaired by touching up with epoxy topcoat material or air-drying enamel. Elastomeric Rain Erosion-Resistant Coating (MIL-C-85322) Elastomeric coatings are used as a coating system to protect exterior laminated plastic parts of high-speed aircraft, missiles, and helicopter rotary blades from rain erosion in flight. They offer good resistance to weather and aromatic fuels in addition to rain erosion. Excellent bonding is obtained after a 7-day drying period. Repair to these coatings in the field is not practical due to this long curing time. Kits are available for repair of coatings where limited touch-up is required. These kits contain a primer, neoprene topcoat, and antistatic coating. If the radome or leading edge coatings are in bad condition, they should be stripped completely and recoated with epoxy primer and acrylic topcoat as a temporary measure. If schedules and conditions permit adequate curing of elastomeric coatings, the original coatings may be replaced. The repair kits are normally bought as an open purchase to ensure that fresh materials are available. Since heat accelerates aging, repair kits should be stored in a cool place or refrigerated. Stripping of fiber glass surfaces should be done according to current maintenance instructions. Elastomeric coatings are toxic and flammable, and must be used with care. PAINTING EQUIPMENT (SPRAY GUNS) The spray gun atomizes the material to be sprayed, and the operator directs and controls the spray pattern through manipulation and minor adjustments of the spray gun. Spray guns are usually classed as either a suction-feed or pressure-feed type. The type of spray gun can be determined by two methods-by the type of container used to hold the paint material and by the method in which the paint is drawn through the air cap assembly. For information on the types of spray guns, refer to NAVAIR 01-1A-509. Suction-Feed Type The suction-feed spray gun is designed for small jobs. The container for the paint is connected to the spray gun by a quick-disconnect fitting, as shown in figure 4-33. The capacity of this container is approximately 1 quart. The fluid tip of this spray gun protrudes through the air cap, as shown in figure 4-34. The air pressure rushing by the fluid tip causes a low-pressure area in front of the tip. This causes paint to be drawn up through the fluid tip, where it is atomized outside the cap by the air pressure. Pressure-Feed Type The pressure-feed spray gun is designed for use on large jobs where a large amount of spray material is to be used. With this type of spray gun, the material is supplied to the gun through a hose from a pressurized tank. This spray gun produces a high volume of spray material metered at a low air pressure. This type of 4-49