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February 18 - February 24, 2013

What causes amine blush in epoxy topcoats?

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Selected Answers

From Thomas Selby of Retired on February 18, 2013:
     Another contributing factor to amine blush is the failure to completely mix the base and catalyst components together or trying to mix partial kits. Either situation can lead to unused catalyst migrating to the coating surface and reacting with the damp air to form a blush.

From Ahmed Abd Ellatif of ENPC on February 28, 2013:
Application in high humidity can cause amine blushing.To avoid it, increase the induction time so the reaction will start in the can.

From Stephen Bothello of Jotun Paints on February 20, 2013:
     Amine blush is caused by the preferential reaction of the amine curing agent with atmospheric carbon dioxide and moisture to form ammonium carbamate compounds. It is typically a SURFACE phenomenon, where the free amine functional groups on the surface film layer combine with Carbon dioxide and humid air (water) to form hydrates of amine carbonates. External risk factors for occurrence of amine blush are high humidity, a difference of  at least 3 C not being maintained between the steel temperature and dew point at the point of application, Cold Wall effect, and low ambient temperatures (dampness). All of the aforesaid risk factors facilitate water availability to the amine by condensation process for the carbamate formation. Intrinsic risk factors attributed to the product are a slow epoxy-amine reaction, improper mixing (excess of curing agent), inadequate mixing (minimum induction time after mixing of base & curing agent mentioned in the data sheet not complied with), presence of low molecular weight amine in the curing agent/ hardener.(These amines are hygroscopic by nature  and easily react with water in preference to epoxy and have high vapor pressure.) Normally, the amine type used in the product can be identified from the Material Safety data sheet.

From Juan I. Ordinas of LOTUM, SA on February 22, 2013:
     Blistering can be seen in water tanks due to amine blush. Typical conditions in water tanks are high humidity and medium to low temperatures. With these conditions amines can react faster with CO2 or humidity than with the  epoxy component, producing a carbamate derivative. This carbamate remains on the surface, and, if it is no detected and removed by solvent wash, when the second layer of material is applied, adhesion fails at this point. Adhesion fails due to this carbamate contamination, and optically you can see blistering, bubbles filled with water between the different coats of the system.

From Jeffrey Seal of Independent on February 18, 2013:
Amine blush is caused by the presence of moisture during the curing process or loss of proper environmental conditions during drying/ curing.

From Bogdan Dana of WOOD GROUP INTEGRITY MANAGEMENT on February 18, 2013:
     Amine blush is caused by the reaction of amine curing agent with atmospheric CO2, leading to a carbamate in the first instance.

From Jorge Lizarraga of International Paint on February 21, 2013:
     1) An excess of amines (Part II) in the mixture of base and converter on the surface of an epoxy topcoat results in amine blush when reacting with CO2 from the air and moisture. Generally, this produces a greasy pink shade on the surface.
      2) A poor mix between the epoxy base (part l), and the amine converter (part ll) will also produce this effect when the free amine reaches the coating surface and reacts with the air. In both cases, the unreacted amine may also produce blistering by water absorption, if it remains inside the film.

From Empty Jasson of Hai Phong on February 22, 2013:
The reasons are 1) induction time does not follow data sheet, so the amine in component B reacts with carbon dioxide in the air to form amine carbamate; 2) too low temperature or high humidity during drying/curing; 3) poor ventilation after paint application.

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Tagged categories: Epoxy; Epoxy amine; Topcoats


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