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August 4 - September 7, 2018

How do you know when pot life has expired? Can you extend pot life and, if so, how?


Selected Answers

From Michael Quaranta of OPERATIONS 40 on September 10, 2018:
It's a good idea to limit this discussion to the average paint or a regularly used two-part coating product. You certainly would not consider increasing the pot life on epoxy coatings. You'd never get it out of the can.

From Trevor Neale of Blastco on September 7, 2018:
This could be an agenda item for the pre-job meeting when the anticipated environment during coating application should be raised with all parties. This will verify that the original specification is appropriate, especially if the environmental conditions have changed; for example, the project timing has changed from a summer to winter application window.

From Zenith Czora of Parex Davco on September 6, 2018:
Pot life is a term that is usually used in two-pack or multi- component coating systems that cure through chemical reaction. Once the components are mixed together, the chemical curing reaction begins. The pot life depends on the chemistry of the curing agents being used. There are slow- curing and fast-curing agents,and, depending on the formulation of the product and its intended performance and application, usually one type of hardener is used or sometimes a combination of different hardeners.Pot life is the time from mixing the components of the paints to the point at which the mixed paint is no longer usable. Pot life also indicates the working time of the product. An increase in viscosity of the mixed paint indicates that it is approaching or passing pot life, which mostly happens in high solids or solventless paints. But low-solids and waterborne products show little or no change in viscosity, even well-past their pot-life. Temperature can affect the pot life and curing time of the mixture. For most two-pack coatings,their specified cure time and pot life are quoted at a temperature of 25C. If the temperature is 10C lower, it will double the pot-life and cure time, and 10C higher will halve the pot-life and cure time. To maintain the recommended pot-life and cure time, the product should be conditioned to suit the environment for at least 24 hours before mixing and application. Low ambient temperature helps lower the temperature of the mixture, slow the curing reaction and therefore prolongs pot-life. Mixing volume will also influence the pot-life of the product. The smaller the volume, the easier it is to keep the mixture cool and the less heat build-up in the mixing pot. Larger volume can generate more heat and accelerate the chemical reaction, thus reducing the pot life. The use of a power mixer at high speed may generate friction that increase heat in the paint mix, resulting in a shorter pot-life. So it is recommended to mix paint under low to medium speed using a power mixer to ensure thorough mixing without generating excess friction. Increasing pot life will also increase curing time. When a coating is applied after pot-life has expired, the cured film may fail in adhesion, chemical resistance, mechanical resistance, gloss and overall film appearance. Never attempt to thin down the mixture, nor add more of either the base or hardener to the mix. Any variance of the recommended mix ratio will result in very poor performance of the coating, and the curing time will generally be longer. So, if extending the pot life is necessary: store all the components in a cool place (not less than 15C) for 42 hours prior to application (two packs are designed to react in the 15 - 25C range); mix components together for 3 minutes at medium speed or hand-mixing for 7 minutes; use smaller pack sizes; select a product with a slower hardener; and store paint in a cool, sheltered place.

From Tom Schwerdt of Texas Department of Transportation on September 5, 2018:
As a followup to Fred: Most commonly, pot life can be extended by reducing temperature of the paint. This is often overlooked in the field.

From Fred Salome of CTI Consultants Pty. Ltd. on September 4, 2018:
Pot life has expired when the time after mixing exceeds that given for pot life on the Technical Data Sheet, for the relevant temperature range. Unless you think you are a chemist who knows exactly how every facet of paint performance can be controlled once the co-reaction has reached this stage, it will be asking for trouble to keep using mixed paint past its stated pot life. Don't do it.

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Tagged categories: Asia Pacific; EMEA (Europe, Middle East and Africa); Good Technical Practice; Latin America; North America; Pot life


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