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El <br />SSPC-SP5 <br />March 1,1Q85 <br />humidity, moisture, contamination, or a corrosive at- <br />mosphere. <br />� <br />moa — The time interval between blast cleaning and <br />rust -back will very greatly from one environment to <br />another. Under mild ambient conditions itimbest 1oblast <br />clean and coat msurface the same day. Severe conditions <br />may require coating more quickly while for exposure under <br />controlled conditions the coating time may beextended. <br />Under nocircumstances should the steel be permitted to <br />rust -back before painting regardless ofthe time elapsed <br />(see Appendix A.G). <br />A.8 OEVV POINT -- Moisture condenses onany sur- <br />face that is colder than the dew point of the surrounding <br />air. it is, therefore, recommended that the temperature of <br />steel surface be at least 5degrees F(3degrees C)above <br />the dew point during dry blast cleaning operations. |tiaad- <br />visable to visually inspect for moisture and periodically <br />check the surface temperature and dew point during blast <br />cleaning operations. It is advisable to visually inspect for <br />moisture and periodically check the surface temperature <br />and dew point during blast cleaning operations. It is im- <br />portant that the application ofpaint over udamp surface <br />be avoided. <br />A.B WET ABRASIVE BLAST CLEANING -- Steel that <br />iowet abrasive blast cleaned may rust rapidly. Clean water <br />should beused for rinsing (studies have shown that water <br />of at |nan\ 15.DODohm-cm resistivity iopreferred>. |tmay be <br />necessary that inhibitors beadded tothe water orapplied <br />to the surface immediately after blast cleaning to tem- <br />porarily prevent rust formation. The coating should then be <br />en-porah!ypreventruothzrnnation.Th00001ingahou|dthonba <br />applied before any rusting is visible. One inhibitive treat- <br />ment for blast cleaned surfaces iswater containing (l32Y6 <br />sodium nitrite and 1.28%byweight secondary ammonium <br />phosphate (dibasic). <br />CAUTION: Some inhibitive treatments may interfere with <br />the performan000fcertain coating systems. <br />A'10 FILM THICKNESS -- It is essential that ample <br />coating beapplied after blast cleaning toadequately cover <br />the peaks of the surface profile. The dry paint film <br />thickness above the peaks ofthe profile should equal the <br />thickness known tobeneeded for the desired protection. !f <br />the dry film thickness over the peaks is inadequate, <br />premature rust -through orfailure will occur. Toassure that <br />coating thicknesses are properly measured, refer toSSPC' <br />PA2.^7WeasuromontofDryPaintThickneoowithK8agnetio <br />Gages." <br />A-11 MAINTENANCE AND REPAIR PAINTING -- <br />When this specification is used in maintenance peinUng, <br />specific instructions should bagiven onthe extent ofsur- <br />face to be blast cleaned or spot blast cleaned to this <br />degree of cleanliness. SSP[-PAGuide 4, "Guide to Main- <br />tenance Repainting with 0\ Base or Alkyd Painting <br />Sys¢ama'^provides adescription ofaccepted practices for <br />retaining old sound point, removing unsound paint. <br />feathering, and spot cleaning. <br />