Rubor de amina

Amine Blushing and Blooming of Epoxy

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By Ing. Toine Dinnissen Dow Deutschland GmbH & Co. OHG
When some epoxy binder systems are applied under low temperature and/or high humidity conditions, a side effect of the curing reaction may appear on the coating or flooring surface. 1 This side effect can manifest itself as grey cloudiness; gloss reduction; a greasy, waxy layer; or whitecrystals or patches. In some instances, it may not be visible; however, in contact with high humidity or water, the coated areas can display opaque white marks. These marks can appear during or after cure. They are the results of two slightly different processes, blushing or blooming. This article will define blushing and blooming of epoxies, explain the causes, describe their effects on coatings, andprovide preventive measures as well as remedies.

Amine blush. Courtesy of the author

This article will help you understand, identify, remedy, and avoid amine blushing and blooming on concrete and other substrates.
Amine bloom. Courtesy of Fitz’s Atlas™ of Coating Defects

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JPCL / December 2005

/ PCE

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Binder Systems in Protective Coatings
Blushing andBlooming Defined Briefly Blushing, sometimes referred to as water spotting, occurs when moisture condenses on a coating surface during the curing process. Sometimes, the moisture can originate from within the porous substrate. Blushing can manifest itself as white patches or it can have a milky, hazy appearance in otherwise clear coatings. It may cause lack of gloss in pigmented coatings. Blooming(or leaching) is somewhat different from blushing. Blooming occurs when the amount of condensate causes water-soluble compounds to migrate from the body of the coating to the coating surface. When the moisture evaporates, the leached components will appear on the surface as sticky deposits. Although the exudate (leachate) is, in principle, water soluble in most cases, it will not wipe off easilywith water, thinners or solvents. Often, the exudate can be removed only by dry or wet sanding after the binder has completely cured. Severe blush or bloom will also
cause significant surface irregularities. These defects are serious enough to cause additional light scattering, resulting in an even more whitened appearance.2 How Do Blush and Bloom Affect Coating Per f o r m a n c e ? Blush andbloom are surface defects that must be avoided when using an epoxy coating because they affect coating performance. They can result in poor gloss retention, discoloration over time (yellowing), and poor overcoating ability as well as poor intercoat adhesion. The most important of these effects is the reduced overcoating ability, that is, insufficient adhesion of a subsequent coating layer to thesystem due to surface energy modification. In the case of the final layer (an epoxy topcoat), the mechanical and chemical properties are altered, and the visual appearance is poor. A phenomenon similar to the surface effects described above can occur at the coating-substrate interface. Moisture that contains dissolved carbon dioxide can cause incomplete cure. If this moisture comes out of a poroussubstrate such as concrete, then the incomplete cure occurs at the coating/concrete interface. The incomplete cure affects the final adhesion, which can explain the occasional delamination of epoxy flooring compounds. Blush and bloom can be removed but this will add time and costs to the coating/flooring job.
JPCL / December 2005 / PCE

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What Causes Blushing and Blooming?Blushing and blooming are chemical reactions.3 The chemical component of the epoxy binder system that causes the blushing or blooming is the curing agent. Typically, low molecular weight (primary-) amine curing agents are hygroscopic (that is, they readily absorb moisture). These amines tend to react with atmospheric carbon dioxide and moisture to form an ammonium carbamate, as represented in the...