For the coating tests, all corrosion, loose coating, and dirt were 

 removed from the 10- and 20-foot elevation test areas on each tower 

 before application of the coatings. A pneumatic chipping hammer removed 

 the larger areas of corrosion and loose coating; this preparation was 

 followed by use of a grinder equipped first with coarse-grit (aluminum 

 oxide #36) and then fine-grit (aluminum oxide #60) disks. The connectors 

 and areas surrounding them were cleaned with a needle gun. 



Two experimental coating systems were applied to each of the chord 

 braces and their leg connectors at the 10- and 20-foot levels of each 

 tower. Appendix B lists the formulations of the experimental coatings. 

 The experimental backpack application equipment was used to apply systems 

 58, 59, and 60. All other systems were applied with a 2-inch wide 

 brush. Appendix C lists the formulas of each two-coat system used on 

 the towers, the material sources, and the total dry film thicknesses. 

 In accordance with Civil Aeronautics Board Regulations, the different 

 levels of the antennas were alternately painted red and white. Random 

 locations on the test areas were assigned to these systems. 



Coating Selection 



The selection of the coating systems for exposure on the vortex 

 towers was two-fold. First, new titanate coupling agents came to the 

 attention of CEL personnel. Coatings containing titanate agents were 

 formulated and exposed in a laboratory salt-spray chamber in accelerated 

 tests discussed earlier in this document. Some of these coatings were 

 selected for long-term exposure on the vortex towers. Second, other 

 coatings selected had proved themselves in applications other than on 

 antenna towers, and it was decided to determine their usefulness as 

 coatings under tower exposure conditions. 



The coating used for the standard for this exposure test was MIL-P- 

 24441 epoxy-polyamide (150 for the primer and 156 for the topcoat). 



Results 



Inspection and rating of the experimental coatings were made monthly, 

 using the ASTM rating system described previously. Exposure ratings 

 after 15 months are shown in Table 5. At this time the coatings located 

 at the 20- foot elevation on the tower nearest the ocean had somewhat 

 greater deterioration than the other. A brief summary of significant 

 effects on the exposed coatings is listed as follows: 



Effect Systems 



Chalking All, except 63 



Discoloration 54, 56, 58, 59, 63 



Cracking 58, 62 



Slight peeling 56 



Rusting, Type I 54, 56, 57, 58, 59 



Rusting, Type II 56, 58 



