tar and others , 

 coatings . 



Table 44 compares the qualities of various types of 



Surface Preparation . 



CI) Methods and Limitations. 



Proper preparation of the surface to 



receive the coating may be the most important activity in a coating job. 

 Regardless of the chemical and physical properties of a coating (such as 

 chemical resistance, moisture resistance, impermeability, abrasion resistance 

 and weather resistance), it cannot properly fulfill its function unless it 

 adheres to the substrate. Proper surface preparation consists of preparing 

 the surface to the proper degree of cleanliness and roughness (surface 

 profile) to receive a specific coating. There are a number of methods used 

 for cleaning and roughening a surface. 



Coatings designed for usage in corrosive environments have been found 

 to give best performance when applied to clean, freshly blasted surfaces. 

 The more resistance or durability expected of a coating system, the better 

 the surface preparation must be. The better surface preparation, the better 

 the performance. Methods of surface preparation have been defined and de- 

 scribed by the Steel Structures Painting Council fSSPC) (1975), and by the 

 National Association of Corrosion Engineers (NACE) (1979) of Houston, Texas. 



Methods of cleaning include hand cleaning with brushes, mechanically 

 cleaning with brushes, and blast cleaning with abrasives. Hand and mechan- 

 ical cleaning procedures are defined and described by SSPC specifications: 

 SSPC-SP-2, Hand Cleaning, and SSPC-SP-3, Mechanical Cleaning. These 

 procedures are usually carried out by using wire brushes. 



Blast cleaning procedures are the preferred method of cleaning as they 

 provide surface roughness (surface profile) as well as cleaning the surface. 

 These procedures, described and defined by the SSPC and NACE, are based on 

 the degree of cleanliness of the surface. All loose surface contamination 

 must be removed. The percent of firmly adhering residues allowed to remain 

 are indicated in Table 45. 



Table 45. Residues permitted to remain on blast-cleaned surfaces. 



Surface Preparation 



Degree of 

 Cleanliness 



Firmly Adhering 

 Material Remaining on 

 Surface (pet) 



SSPC-SP 



NACE 



5 



10 



6 



7 



1 

 2 

 3 

 4 



White Metal 

 Near White 

 Commercial 

 Brush Blast 







5 



33.3 



na 



(2) Immersed Zones . For immersed zones or areas of severe chemical 

 exposures, the surface preparation recommended is "white" metal (SSPC-SP-5; 

 NACE-1). Near white (SSPC-SP-10; NACE-2) is sometimes specified for these 

 same applications but is not as satisfactory and the life expectancy of the 

 coating system will be decreased. The near-white surface preparation blast 



334 



