# Cold weather finishing



## Dan Gal (Sep 17, 2013)

My garage gets down to just below 50F in these winter months. I have a propane heater that can get temps up to 65-70F . I turn the heater off of course when I open the poly to begin finishing and the temperature begins to drop once more in the garage. My first coat dried to the touch long before the garage temp fell below 50 F (a couple hours). My question is, how long after I stop applying the finish must the temperature remain above 55-60 F?

Thanks in advance for your responses'

Dan


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## Jim Frye (Aug 24, 2016)

What does it say on the finish container? I would not go outside of the published range. I have seen reports of poly curing in too cool temps and then having that application crackle under subsequent applications. I'd probably turn the heater back on after I did an application. I use an electric heater in my shop when I'm doing finishing and the temps are below 70 degrees F.


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## Steve Neul (Sep 2, 2011)

The temperature and humidity can greatly affect finishing work. While it may not stop you it may cause you to let the finish dry for days between coats. A lot of finish manufacturers keep a 50 degree threshold because they know most people are not patient enough to allow the finish to dry at lower temperatures. In hot weather you may be able to put two coats of oil based polyurethane on in a day. At 50 degrees overnight drying time is needed. At 40 degrees the finish is likely to be 48 hours before the finish is ready for another coat. At about freezing it's likely to take a week to dry enough for another coat.


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## Dan Gal (Sep 17, 2013)

Thanks for the input so far things have been going well with overnight drying time.


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## Steve Neul (Sep 2, 2011)

Dan Gal said:


> Thanks for the input so far things have been going well with overnight drying time.


You can finish in colder weather than the directions say. You just need to be overly cautious. You can't always go by the way if feels even if you do the thumbprint test. If you put other coats over a finish that isn't ready it might be spring before it dries. Often the outcome is good but can turn out bad. The biggest side effect is the finish would be gummy, soft and easily damaged until it fully cures. The outer layer which would dry first could also crack when the lower coats cure and shrink. I've seen finishes that look like tempered glass when it breaks, just thousands of tiny hairline cracks. 

The thumbprint is most often done with lacquer. You press your thumb on the finish as hard as you can and see if it leaves your thumbprint in the finish. If you can leave a print the finish is definitely not ready. Lacquer works completely different though. You could work with it 20 degrees below zero and while the drying time would be longer it would work. In fact it's more affected by ventilation than temperature. Even that cold a strong fan on it would make it dry nearly as fast as warm weather.


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## FISHEAD (Jan 19, 2011)

*spraying LAC in the 40s*

hi
I too am trying to spray in less than ideal conditions and am spraying ML Campbell Magnasand and Magnamax
precat lacquer.I have been told I need  minimum 65 F relative humidity 40-50% range..I have sprayed in the low 50s but am curious can i spray in the 40s?
thanks


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## Steve Neul (Sep 2, 2011)

FISHEAD said:


> hi
> I too am trying to spray in less than ideal conditions and am spraying ML Campbell Magnasand and Magnamax
> precat lacquer.I have been told I need  minimum 65 F relative humidity 40-50% range..I have sprayed in the low 50s but am curious can i spray in the 40s?
> thanks


I use lacquer the most of all the finishes. Temperature just affects the drying time. I spray it all the time in the 40 degree range. I have also sprayed it when below zero. At that temperature you have to thin it a little more as it gets pretty thick but works fine. Once it is dry to touch where dust isn't an issue fresh air blowing on it helps more than anything making it dry.


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## FISHEAD (Jan 19, 2011)

Thanks for the reply I will give it a shot once I get caught up on other projects


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## Dan Gal (Sep 17, 2013)

How do you handle the over spray in a closed garage?


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## Steve Neul (Sep 2, 2011)

Overspray depends on the finish. If you are using lacquer it might make a cloud in the garage but doesn't stick to anything. If you are using a slow drying finish like an enamel it would be best to do it outdoors. Another option would be to construct an exhaust fan and rig a spray booth. The fan would have to be a belt driven fan such as a furnace blower. Just be sure to mount the motor outside the area where the draw of paint would be. An electric motor creates a spark.


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