With the onset of cooler, damp weather of late summer/early fall brings the
possibility of a troublesome paint problem called Epoxy Blush. Here's
what Epoxy Blush is with some tips of how to prevent it.
EPOXY BLUSH
Amine-cured epoxy formulations are widely used in
ambient temperature cured coatings, like Mil-PRF-22750. If
amine-cured epoxy resins polymerize during conditions of cool ambient
temperatures or high humidity, i.e. condensation on the coating, they may
develop an amine blush, also called epoxy blush. The amine at the coating
surface develops as an oily, waxy or milky film, sometimes amber to clear in
color.
The amine component reacts with moisture and
atmospheric carbon dioxide to form ammonium bicarbonate and/or ammonium
carbamate. This may or may not be visible on the coating's surface but can
interfere with adhesion if over-coated. Contractors and inspectors should be
alert to this phenomena and test suspect surfaces.
These amine compounds are often hygroscopic and very
efficient scavengers of carbon dioxide from the air, even though carbon dioxide
is generally present in low concentrations in outdoor environments. In indoor
environments with human activity carbon dioxide may be increased 2-3 times. In
the presence of gas burning motors (fork lifts, tow motors) and salamanders
etc., the carbon dioxide would be even greater. These sources of heat may also
produce copious quantities of water vapor resulting is exacerbated blushing
problems.
If amine blush/epoxy blush is detected it should be
removed. Thorough washing of the surface with water and detergent (contact
coating manufacturer) is recommended followed by retesting to ensure complete
removal. Recoating is sometimes necessary.
Call me @ 609-636-5858 if you need more information on this problem or how to fix it. And visit our website, www.aerocoat.com , View our Newsletters, to review our other Knowledge Base articles.
Dick Creek
