April 9 - April 15, 2012
How do you know when pot life has expired? Can you extend pot life and, if so, how?
richard d souza of stoncor middle east llc on
April 12, 2012:
Generally speaking, pot life for solvent/solvent free products is influence by the starting temperature of the components and the epoxy/hardener reaction speed. In traditional systems, the end of pot life is signalled by exothermicity and doubling of viscosity of the product mix up to the final gel.
We do recommend the keeping the components in a cooler environment and bringing them to site just before application and mix them at as low temp as practically possible; and, in addition, mix the product in wide mouth or flat containers to extend pot life.
If it is a flooring product, we recommend the mixed product be immediately spread over the floor to allow dessipation of heat of exthermocity, and this will extend the pot life to large extent. You may also want to consider mixing and applying coatings during the cooler times of the day, such as early morning or late evening, keeping the mixed material away from direct sunlight. If it is a solvent-based product, use of slower thinners would also help in extending pot life to a large extent. However, we do not recommend the addition of further solvent or fresh mixed material when the viscosity of the mixed system becomes too high, even though this may be the most common practice for many workers with corresponding solvent-based systems.
remko tas of Futuro SRL on
April 11, 2012:
Pot life is extended when the temperature is low, but care should be taken that both components are already cold before mixing. This in itself poses already a problem because some 2- component paints actually need an induction time, at the right (not too cold) temperature. If the components have a normal temperature before mixing, the chemical reaction starts and produces it´s own heat, especially when the mixed quantities are big. Putting leftovers in the freezer may not work because the heat produced will overcome the cooling of the fridge. Taking into account the risk of failure and subsecuental repair costs, it is a not a good idea to play with this matter and simply prepare less quantities more often.
Tom Selby of Rodda Paint Corporation on
April 10, 2012:
These questions are best answered by the coating manufacturer, either by phone or reading the product data sheet. The environmental temperature will affect the coating's temperature, which in turn will change the pot life time. Any posted pot life time on a product data sheet will be at a lab temperature of approximately 68 degrees Fahrenheit. Characteristics of a catalyzed coating reaching the end of its shelf life can be determined by the product data or a phone call to the manufacturer's technical service department. These characteristics can be a loss of body causing sagging of the coating on vertical surfaces or a thickening of the mixed product and a build-up of heat. Reducing the temperature of the coating's components can extend the pot life but could also affect the workability of the coating. Here again, a phone call to the coating manufacturer's technical service people is where you will find any possible procedure for pot life extension.
Simon Hope of BIS Salamis (M&I) on
April 10, 2012:
Pot life on the whole is quite simple. Pot life refers to the window of time that a two-pack coating, once mixed, is able to be used and achieve its specified performance. The pot life of a material is normally determined by the manufacturer and should be found on their technical data sheet. The time starts from the moment the two components are added to each other.
A series of times will be shown for a variety of temperatures. Pot life is a function of temperature as it is determined by the degree of reaction of the two components of the coating. A 10 degree C rise in temperature effectively halves the potlife and a 10 degree C drop doubles it. (This is the temperature of the coating in the tin, not the substrate or ambient air temp!) Also, you need to be aware that most reactions are exothermic, that is to say, they generate heat, and will, as the temperature rises, reduce the working potlife.There are a string of myths relating to extending potlife, the biggest being the addition of solvents. Solvent does not stop the reaction; all it does is effectivly lubricate the forming polymer chains and allow them to move more freely with respect to each other in the same way as olive oil does when added to spaghetti!
Other myths such as pouring water on the surface, covering with a rag, putting the lid back on, etc., are all similar fallacies and have a habit of leading to spectacular failures!! The only method of extending pot life is to drop thetemperature of the material before use by storing in a cool place for several hours. This can be done using a refrigerated container or at least putting the materials in the shade and out of direct heat and sunlight. Beware, though, of condensation forming and contaminating the materials when taken out into a warm humid area! There is one golden rule that should be always followed and that is never mix up more paint than you can use within the specified potlife, but be very careful to mix to exact ratio and not guess.
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