Using finish after its potlife

      What are the consequences, and how can potlife be extended? July 24, 2002

Question
We use ML Campbell's catalyzed primer, which is not supposed to be used after a certain number of hours. What happens if you use it outside that time limit? I hate to throw away primer or paint at the end of the day just because I didn't use quite as much as I thought I would.

Forum Responses
From contributor H:
Two-component materials are stupid. They do not know the difference between the parts you are coating and the inside of your spray system. At worst, you have a boat anchor, at best, especially if it is cool outside, you have used up one of your lives and used up materials that would go to waste. The pot life is time and temperature, so there is some latitude if the temperature is cooler. This is just a problem that we all encounter.



I think contributor H was trying to say that if you have left-over catalyzed product at the end of the day, you can refrigerate it to slow down the catalyzation so you can use it the next day. Also, with some products, you can catalyze a new batch the next day and pour it in with old to get a good mixture to use. Read the specs on the products that you use to see what is recommended by the manufacturer of the product. If it is a fast product with no pot life, you will know it right away as it solidifies.


Refrigerate after use to slow it from curing. I always add virgin material to the catalyzed material without any problems, then put it in the freezer and remember how much I need to catalyze it when I went to use it again. But check with the manufacturer first.


From contributor S:
It's not the big problem people seem to feel it is, as there are two solutions, both of which have been explained above.

1) What you are trying to do is slow down a chemical reaction. The best way to do this is to remove energy (in this case heat) from the system. Cooling the catalyzed material will certainly do this, and since I live in Phoenix, this is something I've learned how to do.

2) Or you can reduce the percentage of catalyst in solution, which also slows down the chemical reaction. This you do by adding virgin material to the catalyzed material. When you want to use the material again (say the next morning), you add the amount of catalyst that only the virgin material requires. So here we go. You've got a quart left over. Add a gallon of virgin material. Next time you need to use the mixture, add the amount of catalyst needed for the gallon that was not catalyzed. This is actually a fairly simple system. If you refrigerate the catalyzed material without adding the virgin material, you can normally get two to three days out of it, as long as it's in the fridge during that time. A generic rule of thumb for chemical reactions is that they double in speed for each 10 degrees C from room temperature (considered to be 25C). They also slow by half for each 10C below room temperature, so if you put a catalyzed mixture that would have an 8 hour pot life at 25C into a 5C refrigerator, its pot life would become about four times as long, or 32 hours. Another example of better living through chemistry.



I try and mix the correct amount of material that I need to spray. Maybe I'm just old fashioned...


From the original questioner:
What happens if you use the material, as it still seems plenty viscous even after 2 days? I am using ML Campell's Clawlock primer. Would the coating fail, or would there be a bad chemical reaction?


From contributor S:
You'll never know until you try and I personally haven't got the guts to try it. The viscosity, perhaps, isn't the issue. I think the issue is that the resin molecules would be starting to cross link or amalgamate. This could cause a seedy (or gritty) film to form, since the previously independent and dispersed resin molecules would now be much bigger. Since they would be bigger, they would penetrate into the wood less easily and possibly cause adhesion issues. These are educated guesses based on a chemistry background and I think my theory sounds pretty good, but hell, I don't know. Call up Campbell and ask their chemist. It's his job to know.


Been there, done that... Don't do it. When it starts to gel, it won't work. It'll just be a big mess.


I refrigerate my Clawlock at the end of the day. I'll just stick my cupgun in the breakroom fridge, then add another quart to it in the morning with extra thinner and it's been working so far. I will never again try to use it after two days of cooking, however. It becomes too brittle, won't adhere and won't accept topcoat as well.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
I have done plenty of testing of materials that have been catalyzed over periods of time. All of the above ideas are sound ones to a point. I have found that the longer material is catalyzed and crosslinking after its initial pot life schedule per supplier's recommendation, you will start losing chemical resistance properties. You may get wrinkling when you apply the next coat (even if the next coat is fresh) or you may get failure out in the field. Bottom line is that I would pitch any material that was first catalyzed several days earlier even if you used the "virgin" method. You will still have material that has been reacting from the initial catalyzation.



Comment from contributor R:
Some catalyzed finishes can be preserved by adding the exact amount of uncatalyzed finish to the batch and then catalyzing that amount the next day.

For example: To 1 gallon catalyzed finish add 1 gallon of virgin finish material uncatalyzed to stop the reaction. There usually won't be enough catalyst in the batch to crosslink the extra that was added so it will hold over till the next day. Just prior to spraying the next day, add the correct amount of catalyst for the 1 gallon you added the day before.

This does not work with everyone's coatings, so you have to do a small test batch to see how it fits with the products you spray.

Many large manufacturers do it this way successfully.



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