Heating Finishes in the Can

Ways to keep finishes warm overnight in an unheated building. December 27, 2006

Our small shop, which tends to get into the 40's at night in the somewhat-brief winter here in Charleston, just converted to using conversion varnish exclusively - pigmented and clear. We have been warned that colder weather can cause problems with CV that you don't necessarily get from pre-cats or non-cats. First off is curing temperature, which is solved by our heater. We keep the shop warm enough for the crosslinking to happen. Second, however, is material viscosity at low temps. You either have to thin it to make it flow, or heat it to make it less viscous. We don't want to thin it any more than necessary. Our paint supplier only offers a 5-gallon paint warmer. We don't need a 5. We need a 1, since we'll likely never catalyze 5 gallons of anything for a day. Are there any DIY ways of warming the lacquer safely, or can someone recommend a reasonably priced 1-gallon can warmer?

Forum Responses
(Finishing Forum)
From contributor W:
We found one for cheap on E-bay that is a band type heater. You just wrap it around the can. It works just like an electric blanket.

From contributor R:
Most catalyzed finishes (both pre and post cat) need to be around 68 degrees for about 6 hours after being sprayed to cross link properly. Yes, you can heat a finish to reduce its viscosity, but do you want to spray an 80 degree finish on a piece of wood that is 40 degrees? Probably not. Apart from cross linking issues, the cool temps also pose the problem of recoat windows. This is normally more pronounced in the post-cats than the precats. In cool temps, post-cats are more likely to wrinkle if you spray a coat today and then wait overnight to recoat.

From contributor V:
I can suggest two really safe ways. The first is the radiator type heaters that you can buy most anywhere. They are electric and have thermostats on some. Totally enclosed and safe. The other would be electric blankets.

From contributor F:
A couple more inexpensive options: A thermostatically-controlled heat belt from the wine and beer making supply store, where you can also get a stick-on thermometer, or find a waterbed heater at a second hand store.

From the original questioner:
Thanks for the ideas. We thought about a heating pad, which may be the best idea yet, but it seems like it would be slow. Contributor R, thanks for the advice. I was aware of the temp needed for crosslinking. We keep the shop quite warm while we are working, we just don't run the heat in the evening. Just isn't an option in our current building.

From contributor R:
You may want to check with the manufacturer of the coating. I believe you need to keep it around 68 degrees for 48 hours to complete the crosslinking, or else the reaction stops and the finish fractures 6 months from now.