hardness, ahrasion resistance, and chemical resistance. Their limitations 

 include somewhat less weather resistance than certain alkyd coatings. They 

 possess only fair gloss retention and are applied at comparatively low film 

 thicknesses. They also require good surface preparation for best performance. 

 Many phenolics become brittle with age. 



(11) Polyurethanes . These generic class products, more commonly 

 called "urethanes," are usually comprised of either moisture- cured, single- 

 packaged systems, one single package which requires heat to cure, or two- 

 packaged catalyst-cured types. All urethanes contain isocyanate. The 

 single package systems include one which cures by reaction with moisture 

 and one which is cured by heat. The two-packaged systems are cured by 

 reaction with a curing agent such as an hydroxl-bearing polyols. 



Due to the wide variety of formulations available, the selection of the 

 proper urethane for a specific job is often difficult. Chemical resistance 

 (fumes, splashes, and spills), especially with those cured by hydroxl-bearing 

 polyols, is very good. Others may be somewhat limited in this respect. 

 These type coatings are best known for their toughness and resistance to 

 abrasion and impact. The urethanes based on an aliphatic resin possess 

 outstanding resistance to sunlight and weather including excellent gloss 

 retention. These are used extensively on ships and aircraft where color 

 retention is important. Other urethane formulations based on aromatic 

 urethane resins have poor weather resistance. They should not be used as 

 exterior coatings. 



Adhesion properties are fairly good to properly primed metal or direct 

 to masonry. Urethanes also adhere generally well when directly applied to 

 fiberglass materials. There are some formulations which have high build 

 properties. Many urethanes have excellent low temperature cure character- 

 istics and may be used at temperatures as low as 2 Celsius (35 Fahrenheit) . 

 Urethanes have excellent flexibility and elongation properties. Because of 

 the inertness of the two-component polyurethanes, repairability and recoating 

 can be difficult due to adhesion problems. 



(12) Vinyls . This class includes all polymers and copolymers of 

 vinyl chloride with vinyl acetate and vinylidene chloride. They are 

 single-packaged coatings and cure by solvent evaporation. Vinyls are also 

 processed with oil base materials such as alkyds, phenolics, and acrylics. 

 Most offer good overall corrosion resistance. They are somewhat similar in 

 this respect to chlorinated rubber. 



Vinyls withstand high humidity and are comparable to epoxies in many 

 respects in resistance to salt atmospheres and immersion in water. They 

 have good abrasion and impact resistance. Flexibility and elongation 

 properties of vinyl coatings are good. Vinyls are among the best coatings 

 from standpoint of resistance to oxidation. Many have good gloss retention. 

 Their repairability is very good, and they usually present very few problems 

 on recoating. Resistant to most solvents, however, is poor and they have a 

 limited heat resistance. 



(13) Inorganic Zinc . These products are formulated with metallic 

 zinc dust, at relatively high pigment volume concentration, with inorganic 

 binders. Metallic zinc content is 60 to 90 percent by volume in the dried 



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