Priming in the cold

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TRF Supporter
Jul 14, 2015
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Northern NJ
On the off-chance that anyone can reply very soon:

I have an unexpected and very brief window where I could spray some Rusto Filler/Primer. However, it's 40 degrees out, and probably won't be staying in the 30's and 40's for many days to come.

The can says minimum of 50 degrees, but I'm wondering what happens if it's colder. The rocket and paint will be warm when the spray is applied; it's basically the drying/curing that would be affected, and whatever the effect is of spraying through the cold air. I wouldn't dare mess around with topcoats like this, but was just wondering if primer is really so sensitive. I could let it dry for as long as it takes (it will have to dry in my shed, so it will be cold).

This probably won't happen today, but with winter coming I'm curious to hear the answers anyway. If I had my act together sooner I would have sent Rustoleum the question as well (maybe I still will, but that won't help me for today). But generally they're not keen on telling people to violate the instructions on the can, so I don't know if they'd give me a brutally honest answer anyway.
I've sprayed primer in the cold quickly, about 30 degrees F and immediately came in to a warm shop. Used Plastikote primer and it works O.K. Don't shoot color
out in the cold. Save that for Spring or invest in a spray booth. Wife killed me for overspray hitting her car and giving it a gritty feeling. Nothing that a little
Acetone took care of. I learned my lesson there. Kurt
I would think if you brought a warm rocket with warm paint (stand the can in some warm water first to help warm it up), painted, then brought it back inside to cure you would be OK. Not too sure about leaving it out in the cold to cure
In cold temps a few things happen. It also matters if the can of paint is also cold, or is at warmer room temps before spraying. In cold temps the viscosity of the paint can lead it to not properly atomizing, with sputtering rather than spraying. Coverage can be spotty, literally.

If it sprays ok, it may not 'flow' on the surface, and you need a lot more time between primer coats or it will sag and run.
If the paint isn't cold and your surface isn't cold, and you don't rush it, you may be ok.
As others have mentioned, allow extra time for it to cure. If you bring it into a warmer area to cure (like on the dining room table?), be prepared for strong odors as it offgasses the solvents.
I've got pictures of some of our rockets on sticks in the snow while we were painting them with Rustoleum. I've not had an issue yet.
I would think if you brought a warm rocket with warm paint (stand the can in some warm water first to help warm it up), painted, then brought it back inside to cure you would be OK. Not too sure about leaving it out in the cold to cure

I did exactly this yesterday (40 deg F) using Rusto filler/sandable primer (the grey stuff). Works just fine for a small job.
If there's higher humidity, but its warm out, I'll paint.
I keep my cans inside, so If its cold, but the humidity is low, I'll paint.
Small benefit of bachelorhood: I can bring rockets in to dry. Exhaust fans ftw.

Unfortunately, Its 45 F and 95% humid right now, so I'm stuck in no-spray limbo until one of those conditions turns favorable.
I decided to give it a shot. Temp around 45 F, low humidity. In the shed to dry in the cold, we'll see how it turns out (wet paint is not coming into the house, assuming I want to keep my head attached to the rest of my body...). I'll check on it in a week.
Here's my :2:

I am usually more concerned with having the opportunity to paint so I paint in what ever the current conditions are. I have found that when painting in cold weather, having a warm surface and warm paint goes a long way to a nice finish.

I have had a few times where I forgot to turn on the shop heater (I have to paint outside) before painting and the finish just never cured completely. I have stripped the finish and resprayed with the same can of paint on several occasions and achieved a good cure in a heated space enough times that I believe the most important time for optimal conditions would be during the curing stage. If you are using lacquers, stay with warm and dry conditions.
I'll report back here when I've determined how things turned out. I would never try this with a color coat, but I'm hoping primer will work out, especially since I'll be sanding most of it off anyway. Unfortunately it will have to cure (at least most of the way) in 40-some degree weather, which is old but not that far below the recommended 50. We'll see how it goes.
FYI, and not really what you are asking, but ....

I bought a propane heater, and I have used a combination of it and a little electric air heater to heat my garage until it is warm enough to paint. Also clears out the humidity, although that normally isn't a problem in winter anyway.
I paint more in the cold than warm , rocket and paint are both 70* + before going outside for spraying , drying is 70* + in garage
I find that if the rocket and spray can are kept warm that it'll work. The main problem I get is that the fine spray of primer can get frozen on its way to the rocket and I'll end up with a slightly coarse surface. I'll sometimes spray closer to the rocket, at the risk of over spraying, but that's a problem that can be quickly cured with sanding versus having frozen primer not stick properly to the rocket.

Spraying in my garage with the main door open is often a compromise that works well and keeps the cold blast of winter air from affecting the paint.
As others have mentioned the only real trick to priming or painting outdoors or in a cold garage is:

The surface being primed or painted and the spray paint can need to be about 60degrees f. This is easy to do by keeping the rocket in the house at whatever the home heater is set and pre-warm the Spray can by sitting it in HOT tap water for about 3-5 minutes. Run out spray the entire model then quickly return it to the warmth of the house to cure.
Primer or finish color coats work about the same. Just be careful not to over apply the color coats in a hurry which can & will caused runs.
After almost exactly two days in the cold, I brought the rocket inside today. It's still a bit smelly but not too bad. At this point, it looks pretty much like any other rocket after I've applied filler/primer. I'll give it a few more days and then try out some sanding.
Just for the heck of it I'll put my 2 cents in.
I spray all the time in cold weather.
I step out the door, spray, come back in.
But...the mist from the can to rocket cools very fast and will run like crazy on finish coats.
I have a little electric heater I rotate the rocket in front of before and after spraying.
I do this on primer as well as finish coats.
I don't have an option as I now live in an apartment.
Typically, I will let a primed rocket sit for at least a week before sanding, in any weather.
I usually have so many builds going at one time it doesn't bother schedule to finish.
I do the same on finish coats for taping other colors, just cause I can.