clean is usually reserved for slightly less corrosive exposures such as 

 nonimmersion marine. Commercial blast- cleaning surface preparation (SSPC- 

 SP-6 or NACE-3} is utilized for still less corrosive exposures such as mild 

 marine or industrial exposure. Table 46 shows recommended surface prepara- 

 tion for maximum results with specific generic classes of coating. 



Table 46. Recommended surface preparation for specified coatings. 



Coating Type 





Surface 



Preparation 





Alkyds 



Commercial 



Blast 1 



SSPC-SP-6 



NACE 



#3 



Acrylic Enamel 



Commercial 



Blast 1 



SSPC-SP-6 



NACE 



#3 



Acrylic Latex 



Commercial 



Blast 1 



SSPC-SP-6 



NACE 



#3 



Chlorinated Rubber 



Commercial 



Blast 2 



SSPC-SP-6 



NACE 



#3 



Coal -Tar Coatings 



Commercial 



Blast 2 



SSPC-SP-6 



NACE 



#3 



Epoxies 



Near White 



Blast 3 



SSPC-SP-10 



NACE 



#2 



Epoxy-Phenolics 



Commercial 



Blast 1 



SSPC-SP-6 



NACE 



#3 



Phenolics 



Near-White 



Blast 3 



SSPC-SP-10 



NACE 



#2 



Modified Phenolics 



Commercial 



Blast 1 



SSPC-SP-6 



NACE 



#3 



Polyur ethane 



Commercial 



Blast 2 



SSPC-SP-6 



NACE 



#3 



Vinyls 



Commercial 



Blast 2 



SSPC-SP-6 



NACE 



#3 



Zinc (inorganic) 



White Meta] 



L Blast 4 



SSPC-SP-5 



NACE 



#1 



Zinc (organic) 



Near-White 



Blast 3 



SSPC-SP-10 



NACE 



#2 



1 Where a compromise or alternate is necessary Brush Off Blast 



(SSPC-SP-7) may be used. 

 2 Use Near -White Blast (SSPC-SP-10) for immersion or other severe exposure. 

 3 Use Commercial Blast (SSPC-SP-6) where exposure is not severe. 

 ^Near-White Blast (SSPC-SP-10) may be used where exposure is not severe. 



(3) Abrasives . In addition to the degree of surface cleanliness 

 recommended in Table 45, it is necessary that close attention be given to 

 the surface roughness (profile), as illustrated in Figure 95. If the 

 pattern of peaks and valleys is too shallow, proper adhesion may not be 

 obtained and if the pattern is too deep and irregular, pinpoint rusting can 

 occur because the prime or first coat may not cover the peaks. Generally, 

 it is believed that the anchor pattern should not exceed one-half of the 

 dry film thickness of the first coating applied (the prime coat). This, 

 however, is not always true for high build primers or mastics. 



For surface preparation, the manufacturers' recommendations with 

 respect to the degree of cleanliness and the depth of the anchor pattern 

 should always be carefully followed. 



Table 47 indicates the average height of profile produced by different 

 abrasives. The profiles will vary to some extent, with the angle and 

 velocity of the abrasive particles and different hardnesses of the steel 

 surfaces being blasted. Under most conditions, it is possible to protect 

 the surface with a coating system which provides a total dry film thickness 

 of 0.13 to 0.25 millimeter (5 to 10 mils). 



335 



