Painting Applications

Miscellaneous

OUT GASSING FROM COATINGS APPLIED TO POROUS CASTINGS

Q: I read that coatings that bake at elevated temperatures (> 250^oF) might not be suitable for application to porous castings due to their potential to “out gas”.  What does this mean?

A: In this context “out gassing” refers to the expansion of the entrapped air inside the porosities of the castings.  As the coating starts to cure the entrapped air blows its way through the coating causing air bubbles or leaving small holes.  Because the viscosity of the coating at this point is too high to allow for flow, the bubbles or holes do not cover over.  In most cases this is simply unsightly, but where corrosion resistance is required corrosion will often commence at the points where out gassing occurred.

This problem does not affect regulatory compliance, but does affect the quality of the product, both in appearance and corrosion performance. 

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