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SSPC-SP 5 March 1, 1985 humidity, moisture, contamination, or a corrosive at- to the surface immediately after blast cleaning to tem- mosphere. The time interval between blast cleaning and porarily prevent rust formation.The coating should then be rust-back will vary greatly from one environment to applied before any rusting is visible. One inhibitive treat- another. Under mild ambient conditions it is best to blast ment for blast cleaned surfaces is water containing 0.32% clean and coat a surface the same day. Severe conditions sodium nitrite and 1.289,1a by weight secondary ammonium may require coating more quickly while for exposure under phosphate (dibasic). controlled conditions the coating time may be extended. CAUTION: Some inhibitive treatments may interfere with Under no circumstances should the steel be permitted to the performance of certain coating systems. rust-back before painting.regardless of the time elapsed A.10 FILM THICKNESS — It is essential that ample (see Appendix A.6). coating be applied after blast cleaning to adequately cover A.8 DEW POINT — Moisture condenses on any sur- the peaks of the surface profile. The dry paint film face that is colder than the dew point of the surrounding thickness above the peaks of the profile should equal the air. It is. therefore. recommended that the temperature of thickness known to be needed for the desired protection. If steel surface be at least 5 degrees F (3 degrees C) above the dry film thickness over the peaks is inadequate, the dew point during dry blast cleaning operations. It is ad- premature rust-through or failure will occur.To assure that visable to visually inspect for moisture and periodically coating thicknesses are properly measured, refer to SSPC- check the surface temperature and dew point during blast PA 2, "Measurement of Dry Paint Thickness with Magnetic cleaning operations. It is advisable to visually inspect for Gages." moisture and periodically check the surface temperature A.11 MAINTENANCE. AND REPAIR PAINTING — and dew point during blast cleaning operations. It is im- When this specification is used in maintenance painting, portant that the application of paint over a damp surface specific instructions should be given on the extent of sur- be avoided. face to be blast cleaned or spot blast cleaned to this A.9 WET ABRASIVE BLAST CLEANING — Steel that degree of cleanliness. SSPC-PA Guide 4, "Guide to Main- is wet abrasive blast cleaned may rust rapidly.Clean water tenance Repainting with Oil Base or Alkyd Painting should 4e used for rinsing (studies have shown that water Systems," provides a description of accepted practices for of at least 15,000 ohm-cm resistivity is preferred). It may be retaining old sound paint, removing unsound paint, necessary that inhibitors be added to the water or applied feathering, and spot cleaning. r e 42