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by Ron Joseph
March, 2005
Validating the Shelf Life of a Paint Coating
Q. I am trying to validate an expired paint by conducting a viscosity check.
Simply put, we compare the measured results with the values indicated in the
technical data from the supplier. If it's out of range, then we draw a conclusion
that it cannot be used in mass production.
Is it correct? If not, please advise me the effective way to evaluate the
expired paint.
Thank you in advance.
A. The most important tests for validating the shelf life of a coating are
as follows:
1. When you first open the can of paint lower a clean mixing stick to the bottom
of the can. Feel for sediment that might have settled. If stirring the paint
does not disperse the sediment, then you should discard the paint.
2. Mix the paint in the usual manner and spray or brush it out, depending on
whether it is intended for spraying or brushing. Look for little "seeds"
or small particles in the paint finish. If you see them, and if you cannot filter
them by using a cheesecloth or double cone filters, then you might need to discard
the paint.
3. Check that the viscosity of the paint is still usable and that the paint
can be applied to give good looking finish. If you see defects that you have
not seen before, then discard the paint.
4. Confirm that the paint dries in the required amount of time.
5. If the paint performs in accordance with your expectations, then you should
be able to use it for another 6 months. Many organizations don't go beyond the
additional 6 month period, but I personally think that you can go beyond 6 months
provided that the paint still possesses all of its desirable properties.
Best Wishes,
Ron Joseph
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