FAQ

Welcome to the Frequently Asked Questions (FAQ page). Below we have tried to answer the most common questions people have when they encounter problems with their protective coatings. If you do not find an answer to your question please Email us at lou.vincent@nace.org or call us at 337-993-0686 between 8:00 AM and 5:00 PM Central Standard time. After hours, please call 337-255-6030.

  1. Why did my high gloss acrylic polyurethane finish coat have dull spots the day after application?

    This often happens when the polyurethane is applied late in the work day and the weather turns colder or it rains during the night. If the polyurethane has not cured sufficiently when condensation occurs on its surface, the isocyanate in the polyurethane curing agent reacts preferentially with the surface moisture rather than the base resin and you can get minor problems like dull spots or major problems including wrinkling and soft films.
  1. What is amine blush and what makes it happen?

    Amine blush is an exudate from the curing agent of an amine epoxy that normally occurs when the epoxy is applied under conditions of cool temperature and high relative humidity. Many epoxies will not cure below 410F and the curing reaction is very slow between 400F and 500F. The amines that do not react properly with the base epoxy resin are free to migrate to the surface and combine with moisture and carbon dioxide to form an amine carbamate commonly called amine blush. This blush can be very thin and not readily visible to the naked eye, or it can be very heavy and have a dull, buff color. In either case, the topcoats (especially polyurethanes) cannot penetrate this amine exudate layer and adhere to the underlying epoxy coating. The result is peeling and delamination.

Polyurethane Peeling From Epoxy Due to Amine Blush

  1. Why do specifications call for removal of chlorides prior to and after abrasive blasting?

    Chlorides are water soluble compounds that are found in the atmosphere next to salt water bodies. Depending on the wind currents, these chlorides can evaporate from sea water and be carried several miles inland. When dry they look like grains of salt. They are a contaminant that coatings have difficulty penetrating to reach the substrate. When moisture permeates through the coating that is applied over the chlorides, the chlorides absorb the water and expand, creating pressure under the coating film, resulting in blisters and delamination. Specifications for critical immersion conditions such as chemical tanks might call for removal of all chlorides, sulfates and ferrous ions, whereas less critical immersion conditions might allow for as much as 5µg/cm2 of chloride contaminants, while ambient surfaces might allow as much as 50µg/cm2.

See NACE 5/SSPC 12 Water Jetting Standard for complete details on chloride, sulfate and ferrous ion levels.

  1. What is induction time and why is it important?

    Two component products cure by a chemical reaction between the base resin and the curing agent. Some products, especially older versions of epoxies use base resins and curing agents that are marginally compatible. Induction time is that period of time the applicator must wait between the complete mixing of both components and the actual application. This is done to allow the two components to become partially reacted so that it can be applied properly and cure correctly. If this is not done, particularly at lower temperatures, the epoxy may never cure, or it may not atomize correctly resulting in sags, runs, and pinholes in the film.
     
  2. Is it possible to make an epoxy cure below that magic number of 410F that appear on so many Product Data Sheets?

    Yes, but proceed with care and advice from the coatings manufacturer. There are so-called “kickers” that the coatings manufacturer can provide to accelerate the curing reaction but there can be some serious side effects. These tertiary amines are more than used in the original formula and if they do not react completely with the base epoxy resin, a serious amine blush can occur. Even when they react properly, they can cause a long term embrittlement of the cured film.

    However, there are some special formulae that can cure down to as little as 160F without the fear of amine blush without addition of any “kicker”.
     

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