PAINT BLISTERING

Q. I am in charge of the paint line at a plant where we manufacture a line of timers housed in steel cases. In the past, these housings had been spray painted using conventional equipment. We have recently installed airless spray equipment to take advantage of paint savings due to decreased overspray and to comply with air quality standards. Now we are getting blisters in the paint. Is this due to the airless spray equipment? What can we do to remedy the problem? J.K.

 

A. Although not necessarily a common problem with airless spray equipment, blisters in paint film can occur. Since you didn’t say whether you were using air-drying or baking paints, I will cover both.

Blisters in air-drying paints are rare and can probably be cured by the addition of an anti-foaming agent recommended by your paint supplier for his material. On the other hand, the more common problem of blistering in baked coatings can be caused by insufficient solvent flash-off time between paint application and baking.

Another cause of blistering in baked coatings is excessive heating. This can cause skinning over of the paint film and subsequent blistering from solvent popping. The remedy for this is the use of heat zones in the oven to drive off the solvent before the film cures. Owing to the fact you are now using airless spray equipment, your paint was probably reformulated using less and different solvents. Hence, your cure schedule may have to adjusted.