Paint Bleed Through

Q. In our plant, we started a production line to recondition 55-gallon drums for re-use by various industrial customers. We paint them black with a white band around the middle. We are having problems with bleed thru while painting them. What are the possible solutions? 

A. I hate when that happens! The condition you described, bleed-through, occurs when painting a second coat of paint over another paint that is not cured. The solvents in the second coat are actually dissolving the first coat of paint. To solve this problem, the first coat must be cured before applying the second coat. One of the important properties or stages of a curing paint film is “time to recoat.”

Simply stated, “time to recoat” is the time the paint film must cure, after application, until a second coat of paint can safely be applied. This property is listed in the paint’s product data sheet. If you don’t have the sheet, call your paint supplier. If your present paint doesn’t fit your production schedule, use a faster drying paint or a paint with a shorter “time to recoat.”

Follow up:

Q. Our company has manufactured industrial solvent-based and water-based coatings for the drum reconditioning market for many years.

I interpret the previous question to be a problem with the overspray bleeding through at the time of application. The upper and lower panels are usually applied at the same time, with the middle stripe being applied immediately thereafter (or visa versa). This is a very common problem and solved by adding a flow agent (surfactant) to the first coat so the second coat will flow over and absorb the overspray. Let me know if we can be of any further help.

A. Our interpretations of the first problem differ. The condition he describes as “...pigments floating thru each other...” are caused by a full coat of paint applied over another uncured full coat of paint. Over spray, which comes from the edge of the spray pattern and is not intended to paint the product, would be dryer and the it would manifest itself as discrete particles resulting in a rough finish, similar to a texture finish.

In the first case, I believe the solvents in the second coat are dissolving the first coat of paint. To solve this problem, the first coat must be cured before applying the second coat. One of the important properties or stages of a curing paint film is “time to recoat” which is listed in the paint’s product data sheet. I know he will hate to hear it, but a heat pump between coats may solve his problem. And yes I know, heat bumps cost money.