Catalyzed Coating Pot Life

How long after a two-component paint is catalyzed can it be used?


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Q. How long after a two-component paint is catalyzed can it be used? We are a custom coater and are applying two-component finishes in several colors where high-performance coatings are needed. My painter has been ending his day with several gallons of catalyzed paint left over. I'm old school and hate to throw anything away. M.H.

 

A. As a Depression Era baby, my motto has always been “Waste not, want not.” However, use of catalyzed materials is a different situation. All catalyzed materials have a definite useful life, called “pot life.” They start to gel or cure from the time the components are mixed. In paints, the reaction rate is retarded by the presence of solvents in the formulation. After the coatings are applied, the solvents evaporate, the reaction rate accelerates and the paint film cures. The mixed paint left in the container is also gelling or curing but at a slower rate. This accounts for the fact that a two-component paint can have an eight-hour pot life and a half hour set time.

Since most chemical reaction rates are temperature dependant, it is possible, to save catalyzed coatings by refrigerating them to retard gellation. In other cases, catalyzed materials can be salvaged by adding freshly catalyzed paint on a percentage basis (I don’t advise this unless you really know what you are doing). The rule of thumb is that a batch of catalyzed coating is useful until its viscosity doubles. For example, a catalyzed coating with an initial viscosity of 40 sec on a Zahn cup can be used until its viscosity reaches 80 sec.
 

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