Low temp spraying, PPG's answer

[Lost in NJ]

I contacted PPG and asked them the technical reason for not spraying Concept below 60 degrees.

Here is the answer I got from them.

Dear Sir:

Thank you for your interest in PPG Refinish products. My concern is the low temperatures you are describing. Once you go below 55 degrees the paint stops curing, it doesn't restart if the temp. goes back up. You must maintain at least 55 degrees for a minimum of 24 hrs. Once the paint goes below 55 it permanently loses its ability to reach a full cure.

[Dennis N. Schmidt]

This is true for all isocyanate based systems.

[Mooch]

So even if you jacked the heat up the next day it would never really cure ?
Mooch

[Len]

If you allow it to get too cold for a long enough time it usually will never cure properly. Some materials will cure but not really get as hard as they would under the proper conditions.

[Chris L]

I've only done this once..but a few years ago i painted a van with Omni SS urethane and mixed all of the paint up and forgot the bumper...so i put the gun and all in the fridge until the next morning,then painted the bumper.It cured fine.

[Lost in NJ]

Chris,

What you did makes perfect sense.

You need to keep the paint fluid in the cup. The reaction takes place in the presence of the solvents. If you keep the reaction from happening while in the cup you are fine. But if you do not let the reaction happen while the paint is wet, after spraying, than the chemicals can not interact correctly once the solvents have vented. Now you have a bunch of unreacted iso's laying around in your paint.

I think it needs to be look at like a careful balance of time. You need the iso's to stay liquid long enough to make it to the panel, but once on the panel you want them to set up quick.

That gets me thinking, how long can you keep mixed iso paint in the cold and still have it work? It would be nice to have a little around the next day or two to fix the minor mess ups. There always seems to be an edge that did not quite get paint on it or I back into a panel or that darn swimmer.

[Mooch]

Myself I would like to hear this from more than one factory source before I write it in stone. Too much misleading information on the web. And a lot of it can start from the products work force.

One example is body filler .I called one of the makers and asked about shelf life of an unopened can. Told me 6 months than chuck it. I know that is bull.
Also know I have had the heater go out and didn't get it back on until hours later. Paint cured just fine. JMHO Mooch

[Jon E]

I know that we used to keep activated Awl-Grip 545 epoxy primer in a freezer for weeks at a time and reuse it again without a single problem. It did set up a lot quicker though as I would assume that the chemical reaction(s) had already taken place and it was only held in suspension bacause the solvents weren't allowed to flash off.

[mr.kenny]

I think this would be a good experiment for someone here to try. (If you live in a cold climate)

With some leftover clear; shoot some on a panel & set it outside, (but protected) in the cold & shade for a few days. Then bring it inside or let it warm up in the sun to curing temperature.

After a few days or weeks see if there is any difference in the finish between the properly cured and the delayed cure method.

Inquiring minds want to know.