Spray-Room Temperatures for Conversion Varnish
The chemical reaction that cures conversion varnish is sensitive to temperature. That's why manufacturer specs for temperature conditions during spraying and curing are important. June 18, 2013
Question
I need to spray some Kemvar CV. The spec sheet says it needs to be above 70 degrees to spray and cure. I’m just wondering how important it is to spray at 70 degrees and who has achieved good results at lower temps. I just started using CV this summer and did not have to worry about temp. But now that it is getting colder my shop is usually around 65 degrees.
Forum Responses
(Finishing Forum)
From contributor N:
Go by the spec. You'll be pleased. That said, I get my finish room as warm as I can before starting, then don't run the blower any longer than necessary after I am finished. But before I turn it off, I start drawing air from/through the shop rather than directly from outside to aid in speeding up the temperature recovery process. It's been very cool (like dead of midwest winter) while spraying before, but I've yet to have any issues with curing.
I always just do the best I can to get the temp back up to 70 plus as quickly as possible, then let the work cook (or simmer if you like). If late in the day, or late at night such that I am not working in the main shop, I'll put the freshly sprayed items in there to warm even quicker. If between coats, I always make sure it's been at or above 70 for a full hour before I sand.
From contributor G:
Spraying at 65 isn't going to be a big issue as long as your drying area is at 70. Keep the items you want to spray in the warm room to keep them at temperature, bring them out and spray them. Bring them back into the room, not going to be a problem.
From the original questioner:
I am just curious what people are getting away with as far as spraying CV at colder temps.
From contributor G:
I’m still using my Ceros for just about everything. Had to use my DeWalt for something and boy did I hate that. No ergonomics whatsoever. I keep my room above 55 and my drying area at 68 plus, but I use mostly pre-cats. It is only at 55 when the fan has been going for more than 20 minutes and the temps outside are below 20F. Other than that 65 isn't that hard to keep.
From contributor J:
If your shop is too cold you can warm up the finish by catalyzing, reducing, and submerging in a bucket of hot water. This will help a lot with flow out. You could also reduce with high flash naphtha instead of xylene to slow the set time. Try to dry the parts in a warm area, even if they're sprayed in a cold shop. Kem-Var and CV in general is pretty forgiving when it comes to temperature (I've sprayed in some mighty cold shops).
From the original questioner:
My spray area is in a far corner in my shop and it is a bit cooler back there than the rest of my shop. I am looking into buying a 4000 watt 240 volt electric heater to use back there to warm up my drying area when finishing.
From contributor F:
Not that you would ever spray in this cold of temps but I have seen several that do, but roughly, for every 12 degrees plus or minus to the manufactures recommendations that you spray it will result in doubling (or dividing by two) dry times. So if what you are using needs to be at 70 to yield a 30 minute dry time and you are spraying at 58 that will yield an hour dry time. Warming up the finish will lower the viscosity but when it is being sprayed onto cold parts it can have an adverse effect.
From contributor M:
Conversion varnish uses a catalyst not a hardener. That means there is a chemical reaction caused and by allowing the material to get too cool you stop the reaction and can cause cold checking. (That is why they used to tell you to keep catalyzed material in the refrigerator until next day and mix with fresh material). After spraying CV needs to stay above 65 degrees for 48 hours if I remember correctly to cure properly.
Some people do it and get away with it. If you have ever had to strip and entire job that shattered just one time you will never do it again. (Just do a search on this site for cracked CV finishes). If you have to spray in a cold enviroment go to a finish that handles cold temps better like 2k urethane. Your manufacturer should be able to help you there.
