Hello All,
Does anyone know if shellac is temperature sensitive? I need to finish a couple of small boxes, and my shop, in the winter, is pretty chilly. Around 40 degrees in the mornings. I heat it to about 65 when I am working. I am wondering if these low temperature will cause any issues with its application or curing.
Thanks in advance for any informations.
Replies
Shellac is not temperature sensitive, it’s my go to finish for bowl turnings and furniture and my shop in the winter has about your temperature profile minus 5-10 degrees.
I use a lot of shellac and never experience issues in cold weather. Granted, cold weather around here is 45 degrees but still. No ill effect from this non-curing, alcohol-carrier based finish in colder weather.
If it gets cold enough, everything is temperature sensitive. But you should be OK.
If you know you'll be finishing the next day, bring the shellac in where it's warm. It dries really fast. Keep the shop heated until it cures.
Great! Thanks for the info. That'll help.
My workshop's thermostat is set to keep it above 10C (~50F) at night, and I have it at about 16C (~60F) during the day (higher for glue-ups), so broadly towards the middle of your range. Before I installed climate control and insulation, I did have occasional problems with shellac going milky/opaque. But my understanding is that this is humidity, rather than temperature, that tends to cause it via moisture/condensation -- only that as temperature decreases, so relative humidity rises. The point is that there are two tangled variables at play here -- and a temperature cut-off for one person might still be a bit soggy for someone else, I suspect, depending on ambient climate etc. John_c2's suggestion of keeping it heated while it cures is a good one; but it's probably also worth understanding your shop's humidity cycle (and range) anyway for all sorts of reasons.
You are correct that the problem was humidity. Same thing happens with spray lacquer when sprayed in high humidity. It's called blush. The rapid evaporation of the solvents (alcohol or lacquer thinner) cools the just applied finish and causes water to condense in it as it is drying. Once the alcohol is evaporated, there is no "curing" for shellac, unlike varnishes that cure over a long period with the aid of oxygen. So if you apply the shellac in a relatively warm, dry shop, it will harden quickly, so there won't be a problem with what happens overnight.
Thanks guys, that's great information.