Summary:
Amine-cured epoxy resin formulations are widely used in ambient temperature cured coatings and flooring applications. If polymerization occurs during conditions of cool ambient temperatures or high humidity, such coatings can develop a surface oiliness, exudate, or whitish spots variously referred to as “amine-blush”, “sweating”, or “bloom”. In this article, all such phenomena will be referred to as “blush”. In the literature and at trade shows, proposed solutions to blushing problems are often provided in the form of new amine hardeners, which have been empirically shown to provide improved blush resistance under blush promoting conditions. Seldom, if ever, is information given about formulation and processing strategies that could give the end-users more control over their operations. In this paper I hope to fulfill that need.
Causes of Amine-Blush
Blushing is caused by sorption of moisture and carbon dioxide from the atmosphere during curing. Although the conditions that can cause blushing, as well as the chemistry involved, have been known and reported for some time [1-6], no systematic description of strategies for developing blush-resistant epoxy formulations appears to have been reported. This may in part be due to the fact that epoxy resins and curing agents are often supplied by different companies. Thus technical service in this area often deals with only “half” of the raw materials’ performance at a time, rather than dealing with the performance of the entire system.

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