Humidity and Conversion Varnish Cure Time

Dehumidifying, air-conditioning, or heat drying can speed CV cure times during muggy weather. October 26, 2005

We are experiencing some high humidity problems. Our finish (CV) is not drying too good, which is making it not sand well, which means rough finish. We only have this problem when there has been rain and it is hot outside. I just bought the biggest dehumidifier that I could find. Will this take care of the problem?

Forum Responses
(Finishing Forum)
I use pre-catalyzed lacquer, and use 15% retarder thinner in the mix for humid days. It always fixes the problem for me.

You could add a high flash naptha to speed the drying, but you have to add just enough to keep from causing blush.

Of course, any means of bringing down the humidity level in the booth and drying room will solve blushing problems. Just remember to keep the door closed (and then you maybe will want an AC unit, too).

Glycol ether EB at no more than 2- 2.5% will help.

I partitioned a small section of the shop off and put a cheapo air conditioner in it. After I sprayed a piece, I ran it into the room and closed it back up. Worked great and I can deliver tomorrow instead of next week.

From Paul Snyder, forum technical advisor:
The humidity will slow the dry/cure time of conversion varnish (CV), but blushing is not an issue. Blushing happens with lacquer (and shellac). If waiting longer before sanding is not an option, the dehumidifier should help a lot. You'll want to limit the amount of air that comes into your drying room, but have enough fresh air exchange to get rid of the solvent fumes.

If you raise the temperature in the room in which you spray and you keep the doors closed (if possible), you lower the relative humidity.