This section will cover the basic design considerations that must be 

 given to the structures to be protected and to the selection, application 

 and inspection procedures necessary to provide a protective coating system 

 with years of dependable service life. Repair, rehabilitation, proper 

 maintenance procedures and other important facets, including economics, are 

 also described. 



Protective coatings are designed primarily to isolate metal surfaces 

 from exposure to corrosive elements. Coating thickness will vary from 

 50 to 75 micrometers (2 to 3 mils) for simple alkyd coating systems to 380 

 to 760 micrometers (15 to 30 mils) for certain high build coal tars, coal-tar 

 epoxies or urethanes (1 mil equals 25.4 micrometers or 0.025 millimeter; 

 where any conversion in a discussion results in numbers less than 0.1, micro- 

 meters will be used) . 



Conventional paints, surface preparation and methods of application 

 should not be used in corrosive areas of coastal structures. Only high 

 performance protection coatings such as epoxies, zinc rich, chlorinated 

 rubber, and polyurethanes must be considered. Products selected for use 

 should be resistant to the environment and capable of serving as a barrier 

 between the environment and the substrate. Writing appropriate specifica- 

 tions to cover all facets of the work will play an important role in terms 

 of obtaining the protective coating job desired including, particularly, 

 cost per unit area per year of service life. 



b. Design and Specifications . In the design of new structures, it is 

 important to consider surface requirements for ease of coating application 

 and effectiveness of coating. The design should (1) provide smooth, flat, 

 easily curved surfaces, and (2) avoid overlapping surfaces, edges, back- 

 to-back structures (brackets, beams or L's), riveted surfaces, sharp 

 protrusions, and weld splatter (see Fig. 92). 



Like other personnel in any design and construction organization who 

 are engaged in translating an owners requirement into design and the 

 design into a structure, the protective coating specifier must give careful 

 consideration to all aspects of the coating work requirements. The speci- 

 fication must detail coating selection, surface preparation, coating 

 application, coating inspection, touchup, and repair to ensure a successful 

 job. 



c. Generic Classes . Numerous coastal marine coating tests and surveys 

 of field applications have been made. Table 41 lists some of the coating 

 systems used for various surface substrates. In the discussion which 

 follows, various uses and precautions are presented for each coating system, 

 with a brief description of chemical composition and properties. 



Coatings are composed of many raw materials. These materials can be 

 divided into three categories—vehicle, pigment, and additives as shown 

 in Table 42. The vehicle or liquid part of a coating is composed of 

 resin, solvent, and plasticiser. The vehicle resin contributes to many of 

 the basic properites of a coating including water resistance, chemical 

 resistance, cure time, elongation, toughness, and adhesion to substrate. 



322 



