Selected Answers

From Emil Langiewicz of AkzoNobel on January 12, 2017:
Blistering is caused by reaction of isocyanate (cu ...read more Blistering is caused by reaction of isocyanate (curing agent) in direct contact with water (condensation) where carbon dioxide and alkaline chemicals are formed. Please check pH of the blister fluid to confirm it.

From Bryant Chandler of Greenman-Pedersen, Inc. on November 4, 2016:
If the blistering/crater formation is random but i ...read more If the blistering/crater formation is random but in a vertical pattern on a tank shell, I would suspect the hoist motor spitting out oil droplets when going up and down. Other random spots could be caused by power tool air motors spitting out oil, especially if recently lubricated. I have had contractors wrap cloth around the discharge port on air or electric motors to eliminate a problem or potential problem.

From Paiboonsak S of CFT on November 4, 2016:
It should not be called blistering, maybe bubbling ...read more It should not be called blistering, maybe bubbling, If so, the surface must be very rough and porous. In the case of craters, the surface may have oil, grease, silicone or others contamination. Before topcoating , you have to inspect the surface. It must be very clean with no contamination.

From VCBud Jenkins of CSCS on October 31, 2016:
An unclean, oily surface is the most common reason ...read more An unclean, oily surface is the most common reason for craters. Clean it with soap and water or solvent and rinse it well. Sometimes sanding it will help remove the incompatible surface spots. First, make sure the coating does not have any craters of its own by spraying another clean surface and examining the result.