I may be the case of “a little knowledge can be dangerous (or at least troublesome)”.

In my working life, I worked in the resins and polymers business, selling and marketing to the coatings industry.  Hence, I have some basic understanding of the chemistry, physics, etc. that go into coatings.

I have tried to determine, without success, whether crosslinkined coatings, like conversion varnishes, will have better resistance to moisture vapor transmission.  A FW article on maintaining shop jigs stated that shellac had the very best resistance to moisture vapor transmission.  That reference may have been in the context of easy application.  I recognize catalyzed conversion varnishes or lacquers almost always need to be sprayed to get satisfactory results.  Spraying is not a problem for me and I have had excellent results with catalyzed systems and HVLP.  In terms of overall resistance properties, alkyd resins crosslinked with Urea Formaldehyde or Melamine are outstanding, and of course, two part epoxy is “bullet-proof.”  Often the trade off needs to be the movement of the substrate underneath.  The coating can be “bullet-proof” and still fail because the substrate moves with changes in temp and humidity,  and the extremely hard coating can’t move, resulting in checking, crazing, or complete delamination.  UV resistance can also be a problem, with epoxy being particularly sensitive, and UV degradation of the substrate can accelerate any coating – substrate problems. 

Allowing for the precautions one needs to take when using catalyzed/crosslinked systems, does anyone have any real info / data on moisture vapor transmission?  I have contacted one MAJOR industrial coatings manufacturer ( my supplier) and their “technical expert” provided the terse reply ” we do not test moisture vapor transmission of our products.”

Thanks,

Larry