showed some blistering around the scribed areas, but systems 12, 18, 35, 

 and 38 also had blistering elsewhere. Except for systems 21 and 38, all 

 systems had slight undercutting. All systems, except systems 18 and 30, 

 would probably provide several years of protection to steel under normal 

 exterior exposure. 



Second Series 



Panel Preparation . Shop personnel cleaned the prerusted experi- 

 mental panels by power grinding. The panels were then scrubbed in water 

 with a bristle brush, dipped in MEK, and allowed to dry. All coatings 

 were applied by spraying, using the experimental backpack applicator." 

 Systems 54, 55, 57, 58, 59, 60, 66, 67, 68, 69, and 70 comprised this 

 series. The types and sources of the coating systems can be found in 

 Appendix A. 



Results . The salt-spray conditions and inspections were similar to 

 those of the first series. All systems were exposed to salt spray for 

 123 days, except systems 55, 57, 67, and 70, which were exposed for only 

 98 days.** After 123 days, systems 69 and 70 had failed because of 

 delamination of the topcoat from the primer. System 67 performed the 

 best (see Table 4) showing only slight overall blistering and blistering 

 scribe. Second best was system 57, which showed discoloration and 

 rusting, Type I. All the other systems showed discoloration, tubercu- 

 lation, and rusting scribes. Systems 55, 67, 68, and 69 showed slight 

 blistering, and systems 54, 58, 59, 60, 66, and 68 showed undercutting. 



CLEANING AND COATING APPLICATION EQUIPMENT 



Three of the most common causes for coating failure on steel towers 

 are: (1) inadequate surface preparation, (2) improper application of 

 the coating, and (3) incompatibility of the new and previous coatings. 

 To reduce coating failures due to (1) or (2) surface preparation and 

 coating application equipment was investigated. As a result of the 

 investigation, special equipment was designed and used in preparation of 

 both the second series laboratory tests and the field tests. 



Design 



This special equipment, shown in Figure 1, was designed for mount- 

 ing on a backpack for a painter to carry it to areas to be coated. The 

 backpack was designed and fabricated by Advanced Coatings and Chemicals, 

 South El Monte, Calif., under a contract awarded by CEL. Three criteria 

 were uppermost in its design: light weight, portability, and sufficient 



*See section on CLEANING AND COATING APPLICATION EQUIPMENT. 



-"'"The 25-day difference in exposure time of some of the panels was due 

 to relocating the salt-spray cabinet. After relocating the cabinet, 

 additional panels were added to the test. 



