(b) Modified Coal-Tar Coatings . Coal-tar coatings are frequently 

 modified with other materials such as epoxy or polyurethane. The modified 

 products have the excellent water resistance of the coal tar with the 

 improved toughness and solvent resistance of the modifier. Properties of 

 coal tar and the modified materials are as follows: 



(1) Coal-tar properties: low cost, excellent resistance 

 to water, low moisture vapor transmission, poor resistance to 

 organic solvents, and poor abrasion resistance and toughness; 



(2) epoxy properties: tough, chemical resistance, and 

 solvent resistance; and 



(31 urethane properties: elastomeric and abrasion 

 resistance. 



Two component coal-tar epoxy and coal-tar urethane coatings are dis- 

 cussed. Coal-tar epoxy systems contain coal tar, pigments, solvents, epoxy 

 resin, and either an aliphatic or aromatic amine or polyamide curing agent. 

 Coal-tar urethanes contain coal tar, pigments, solvent and reactive urethanes. 

 These "chemically cured" coal-tar coatings can be applied in one coat to 

 dry film of 0.13 to 0.64 millimeter (5 to 25 mils). Most coal-tar epoxies 

 have excellent adhesion, abrasion, and impact resistance. Their resistance 

 to immersion effects in salt and fresh water is excellent and they withstand 

 a wide range of chemical corrodents. Proper measurement of two components 

 is mandatory for proper cure and coating properties. It is recommended 

 that these coatings be mixed by use of power mixers. Subsequent coatings 

 must be applied within manufacturers' specified time and temperature 

 limitations to avoid delaminization between coats. The coal-tar epoxies 

 have a variable pot life when mixed depending on the temperature. Repaira- 

 bility is a major problem and color is limited to black. They tend to 

 chalk lightly in sunlight and weather and lose their original black gloss 

 within 6 months to 1 year. 



(8) Epoxies (Catalyzed) . Epoxy coatings are based on epoxy resins 

 and are supplied as two component materials. One component, contains the 

 epoxy resin, the other the curing agent. The two components must be 

 thoroughly mixed before application. A broad spectrum of service conditions 

 is covered by a wide variety of materials based on these versatile resins.' 

 Amine or polyamide type curing agents are most common. Epoxies have 

 excellent durability and toughness and possess high chemical and moisture 

 resistance. They resist strong alkali, and have excellent adhesion proper- 

 ties and abrasion resistance. They may be used in marine environments and 

 are not damaged by moisture or immersion in water. 



Epoxies may be used in conjunction with special fillers to make mastic- 

 like materials which find applications as concrete grouts, surfacers or 

 "bug hole" fillers. These mastics or grouting compounds may be applied as 

 heavy coats by trowel or in some cases by spray. They are used in marine 

 application to protect concrete or steel in the splash zone. Heavy layers 

 of the mastic are built up in the splash and tidal zone. Layers of glass 

 fabric may be introduced, between coats of mastic to add strength to the 

 splash zone coating system. Application is sometimes by hand in a process 



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