Temperature and Humidity Issues When Spraying On Site

Watch out if it's too cool, catalyzed finishes will not properly cross-link. June 8, 2008

I'm going to finish a new library in a pretty large house. It is under new construction. We have heat. The room is all white oak with three different cuts - 1/4 sawn, rotary and rift cut. I plan on doing a mission finish on the room. The room is very dry - 38% humidity. What should the room humidity be before I start finishing?

Forum Responses
(Finishing Forum)
From contributor A:
You haven't stated what finish you will be using, but most coatings are formulated to a standard ideal of 50% humidity at 77F. You should be fine if you can get it up closer, even 42-45. A lot depends on what coating type you are using.

From the original questioner:
I will be using Mohawk vinyl ss and pre-cat flat finish. Today I had to bleach a mahogany door in the room with ab bleach. I put on a light coat of water first to see if there were any blotches. It dried pretty fast. I bleached the door, which seemed to work okay. The temp in the room is 64 degrees and the humidity today was between 36 and 42%.

From contributor R:
I would be more concerned about the temperature at 64 degrees. Optimum conditions would be above 75 degrees throughout the entire spraying period, lasting for at least 72 hours after your last finish coat. That will allow your finish to crosslink and become a durable finish. Spraying at 64 degrees is simply wrong in my estimation.

From contributor C:
You're right - cat lacquer should not be sprayed under 70 degrees; it will not crosslink properly even though it may appear to be alright. Future problems will include cracking.

From the original questioner:
Thanks for your response. I must add that I had the unfortunate experience where I had to spray in temps less than 70 (on site and in a heated garage, but about 65 degrees) and was using MLC glazes and vinyl sealer for many, many doors. I thought everything was fine, but a week later in several areas the coating was shriveling. Complete redo was in order!

From contributor C:
May I inquire if that's the first or only time this has happened to you? Or have you had other experiences such as this, where cold weather was a factor?

From the original questioner:
I think with all the information I have received, I will go with nitrocellulose lacquer. I have used it for over 30 years and have never had a problem with it.

From contributor C:
That should work fine.