Stretching the Pot Life of Conversion Varnish

There are ways to prolong the pot life of conversion varnishes, but they are less than satisfactory and may not be worth the effort. September 16, 2008

Besides disposal, can Krystal CV after the eight hour pot life expires be used up by adding/mixing small amounts with freshly catalyzed CV? This would be applied to concealed areas only. Would the CV still dry/cure but retain a different hardness?

Forum Responses
(Finishing Forum)
From contributor R:
Sure can. I go up to a 50/50 mix.

From contributor B:
I would use the product as is and as soon as possible. It will dry but you will not get the maximum hardness out of it.

When you add catalyst to a finish you start a chemical process; kind of like adding some baking soda to a glass of vinegar. As the baking soda is absorbed by the vinegar two things happen. First the liquid bubbles and foams as a response to the chemical interaction and second depending on how much baking soda you put in it reduces or neutralizes the acid content of the vinegar. You could add more baking soda, but you don’t get much, if any foaming because the vinegar is no longer a strong acid. If you mix a new batch and pour it into the fizzed out first batch the neutralized vinegar in the first batch will dilute the acid content of the new vinegar thus reducing the overall fizz production of the second batch.

Catalyzed finishes are pretty much the same. At the end of the pot life the chemical reaction is pretty much complete. If you add more catalyst it has nothing to react with. If you add freshly catalyzed material the old finish is just going to reduce the effectiveness of the catalyst on the new finish.

From contributor B:

This material should be fine, providing your viscosity has not increased more than 5 to 7 (#2 zahn cup or #4 Ford cup) from its original viscosity. A typical conversion varnish is stable up to 12-16 hours under normal operating conditions. Adding freshly catalyzed material is an excellent idea. However, you may want to consider de-catalyzing! Simply add virgin material to the catalyzed material at a rate of 1:1. This will stabilize the material.

The next morning you add additional catalyst for the amount of virgin material you added the day before. This is an easy way to extend the pot life of conversion varnish. Finishers have been using this method for years and it has been way for small shops to save catalyzed material (not to mention the benefit of not have to dispose of hazardous waste).

From contributor U:
I have extended the pot life of MLC catalyzed duravar and the like by taking unused finish at end of the day and putting in a refrigerator or outside in winter. The cold slows the chemical reaction. I would not stretch beyond 24 hours though. Redo’s are too costly.

From the original questioner:
Thanks everyone for the responses. For now I think I'll play it safe and not re-use it. The disposal costs are cheaper than redo's. I'll use it up on some sample boards and see what the long term results look like.

From contributor R:
Keep some drawer bottom or base cabinet back sheet goods (parts or whole sheet) in the finishing room. Finish out your material on them. Now that material is "prefinished." Cut to size on the next project and go.