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I'm about to brush oil varnish on my first build (Pratt & Lambert, will try Epifanes on my next one). I have a room behind the garage that's partially underground with two small windows up high on one wall. The room doesn't get much air circulation on its own, but I have a casement A/C unit installed in one of the windows that allows me to draw fresh air and keeps the RH around 48%. The fumes should dissipate to some degree as I'm brushing with the A/C running, but when I "close up shop" for the night I turn off the A/C and turn on a dehumidifier (I've found the dehumidifier is considerably cheaper to run).

With the guitar hanging in there to dry with very little fresh air moving about, am I creating a potentially hazardous situation? Can the fumes build up in the room so much that the dehumidifier can set them off?

Call me worried......

Hey, Darren,
It seems to me you have some options. First, you could leave the air conditioner AND the dehumidifier running on the relatively few nights of the year that you might be trying to dry a brushed on varnish. You could try to move your varnish drying operation to a place with better air circulation. (I hung my nitro lacquer sprayed mando near an open, screened garage window for just this reason.) Or you could close everything down as usual and just come in the next morning briefly, fire up the A/C, and go drink a cup of coffee while the A/C exchanges some indoor and outdoor air. I do respect your concern about this. If I were in your specific situation, I think I'd start with the first option. As to your direct question, I have no idea whether this is a dangerous situation or not. But you are worried about it, so....take positive steps to deal with it. I think you'll be fine.

According to the MSDS Pratt and Lambert isn't extremely hazardous. The Health rating is "2". The flammability rating is also "2". It's combustable, but not explosive. (These are the same ratings as Tru-oil.)



No, it's combustable, but not explosive. (Nitro is explosive) Also, Varnish cures by polymerization, not evaporation, so it off gasses pretty quickly.

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I'd worry more about fumes while brushing than while gassing off. The varnish I've used in the past was some stinky stuff indeed. The A/C units I've seen that enable fresh air exchange don't really move much air. possibility to put a fan in the window and pull air out the window while you're applying the finish? (And wear a respirator?)

Thanks for easing my mind. Good to know that if my dehumidifier creates a spark for some unknown reason, I won't be reduced to cinders.

Garry- that's an excellent idea. Hopefully the RH will stay relatively the same. Going to the Home Depot right now to look for a window fan. Thanks!