Exceeding Pot Life on Conversion Varnish
Thoughts on pushing the pot-life envelope with conversion varnish after catalyzing a batch. August 16, 2009
Question
I have sprayed both clear and pigmented conversion varnish that's been catalyzed in the can for over a week for the purpose of samples and small touchups and have never seen any ill effects. Can someone tell me what exactly happens after the 24 hour recommended pot life? What chemically is going on? Is the finish stable, but less durable? Will it fall off? This has more to do with cutting down my waste than saving money.
Forum Responses
(Finishing Forum)
From contributor L:
It's a durability thing. After the pot life is up the chemical reaction (cross linking) is done. The cross linking is what makes a durable finish tough. If you want to put it on the bottoms of lowers or the backs of backs or other unused or unseen areas this would be a good place for it. I wouldn't use it in areas that will be seen or get use.
From contributor B:
I have used it after 24 hours and it did fine. It is just as hard and scratch resistant as the first time I used it. I think it depends on the temperature. I noticed in the cold temps it takes a day or two longer to turn to jelly.
From the original questioner:
Neither the clear or pigmented has ever turned to jelly. We've made catalyzed quarts that my finishers have used months later for small touchups. I guess I'll have to do some scratch testing to see just how much durability is lost. I guess what I want to know is, if the finish cross-links in the can, so what? Does it give me a conversion varnish with the durability of a standard lacquer? Or does it mean something more sinister?
From contributor G:
"Does it give me a conversion varnish with the durability of a standard lacquer?" Yes, maybe a little more durable, but a lot less than it should if it was done within the pot life. If you want to lessen the waste make smaller batches. Spray your waste out of your booth using your gun.
From contributor J:
CV's can be "de-catalyzed" by adding un-catalyzed material and then refrigerating. Then when you are ready to use, add catalyst only for the amount of fresh material that was added to the original left over material. Still, I would only do this for a day or two at the most and even then I would only use this material for back sealing etc. My reputation is worth more to me than a quart of leftover CV.
The thing is, if you ever do have a problem and your finish supplier knows you used it beyond its pot life you could end up in trouble even if that was not the cause of the problem. I have to agree with contributor G - make smaller batches and plan your spraying better to reduce leftover material. Or you could just go with a high quality pre-cat, some of them are getting very good these days, approaching the durability and resistance of conversion varnish without the pot life issue.
From contributor R:
I worked at a shop that used CV for a week that way. I noticed when I was doing touch-up work in the field that I could scratch the finish off with my finger very easily. I have also seen the finish wrinkle when a freshly catalyzed coat is sprayed over one of the "questionable" coats. I wouldn't do it, but then again I don't even like using CV due to the dry film restrictions, formaldehyde off-gassing, sensitivity to temperature and that annoying ability to shatter like broken glass if you break any of the rules.
From contributor B:
Catalyzed material can be stored in a refrigerator to extend its pot life. I recommend trying that if you have a fridge in your shop. Also, if you need to preserve it, catalyzed material can be stored away much longer by adding un-catalyzed material to your catalyzed material. Then when needed, just add your remaining catalyst that you left out when you’re ready to paint. For example, if you have a quart of catalyzed material you want to store, add a quart of un-catalyzed material into it. Then when you are ready to use the material, add the remainder of the catalyst that you left out. Which in this case, you would just add enough catalyst to catalyze one quart of material, even though you have two quarts, because you already added in the catalyst into the first quart.
