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Old 10-12-2005, 08:41 PM
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Crosslinking and Temperature

I've heard different opinions about the minimum required temperature that will allow urethane paint to continue to cure after paint. Some reps have told me 55F, and some have said 60F. Some have said that below that temp, there is virtually NO crosslinking going on (bad), and others have said that below that temp, crosslinking is seriously curtailed, but still occurs. I'm curious to know if anyone here has more detailed info on the subject.

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Old 10-12-2005, 10:27 PM
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Some systems (Glasurit for one) used to claim down to 47 degrees F when using accelerator. A lot has changed (chemistry)since I got that info. If the air temp is 55 degrees it's a good bet that the metal (body temp) will be around 10 degrees colder. I would check with the manufacturer ( try call a tech rep or chemist that works in the lab) and see what reccomendations they have for thier products. I have done jobs with the addition of accelerator down around 50-55 degrees metal temp, that cured well. I think some additional heating is a better solution. Tech sheets for accelerators will give temperature ranges and possibly reducer grade options and cure times. Big jobs can be difficult to do with these products. Also cool temps with high humidity can condense more moisture on to the cold metal surface which can be trapped under or in the paint film.

overspray
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Old 10-13-2005, 09:46 PM
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Part of the reason I'm asking is because we've had some comebacks (none that I have painted,YET) at the shop, and I have a feeling that improper curing is a contributor to the problem. I want to convince the boss to either invest in more IR lamps and/or allow the heat to remain on in the shop overnight. It's expensive for us to get paint cured in the wintertime, but my concern is that most people here park their cars outside, which means the time the job is in our shop the only time curing is taking place, so customers are driving around with half-cured paint all winter long.
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Old 10-13-2005, 11:58 PM
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I was always told paint stopped at around 55 degrees F... I don't know how much of an issue that is in the winter months in cold climates though... I have painted many vehicle in the winter and they always did fine... great thread though... I would like to see where this goes... I am sure Barry will chime in.... I always kept the shop warm too, even through the nights, and usually kept the car/truck/whatever for about a week messing with it ( reassembling, cut and buff etc) before it went to the customer... Maybe that was the difference... It gets cold here in KY
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Old 10-14-2005, 12:35 AM
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I have no idea on this, but on the can of marhyde clear it says not to paint if the temperature is below 55 degrees. Maybe the crosslinking is the reason, I never thought about that. I didn't realize crosslinking would stop below a certain temperature, I thought it would just slow. I know some people stick activated paint in the fridge overnight for use the next day. Will be interesting to know the answer to this, is we get some awefull cold days, and hard to keep the garage heated for a long time for me.
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Old 10-14-2005, 04:37 AM
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I have only been doing body work professionally for a short time, but when I did work at home in the colder months, I always warmed the garage and car for a couple of days before doing any work on it. I them kept it warm for a couple of days after. The last shop that I worked at, one of the older techs told me that they had had a bunch of problems with body work and paint when the owner decided that it cost too much to heat the shop at night. They decided that it was better to keep it warm. In the olden days, all we were concerned with was the lacquer thinner evaporating out of the paint. The enamel was going to take it's time anyway. We just kept it from freezing. We didn't have to worry about all of this complicated stuff.
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Old 10-14-2005, 06:33 AM
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Crashtech, if you cure with IR lamps remember to cure in layers. Make sure the primer is cured first then the topcoat. Also allow the panels to cool and have sufficient time for the solvents to leave. Get some tech info on accelerators and other addatives to help with a faster cure.
Sikkens, for example has an addative (extra top) that is specifically for a faster through cure of the clear or urethane topcoat color. Accelerators are also available to speed things up. Of course a good bake booth is a great choice. I've been painting in cold climate for 35 years and have made use of most of these products and techniques.

overspray
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Old 10-16-2005, 11:50 AM
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Tremco/BF Goodrich did an extensive study in the late 80's and found that all cross-linking slowed down drastically or or came to a halt at about 55 degrees.

Some products are worst than others as 2K primers tend to do a little better at say 50 degrees than clears do.
Epoxies just plain go to H**l at about mid 50's.

A couple of years ago when we wanted to make an accelerator, Jamie did some extensive testing to see what would be the best way to make one.
One thing he found was even the accelerators stopped performing in the low 50's. They helped a little but not much.

We found that the blocked/tin accelerator did work the best but still with limitations.

If you lack heat metal temp before painting is more critical than the out side temp.

I would take 75 deg metal temp and 50 deg air temp over
80 deg air temp and 50 deg metal temp any day.

Also, thought of something that may be of interest. There are specialty companies that make a cold weather epoxy for people that paint outdoors.
Would not work in automotive.

Last edited by BarryK; 10-16-2005 at 12:15 PM.
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Old 10-16-2005, 01:03 PM
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Cold weather

Quote:
Originally Posted by BarryK

If you lack heat metal temp before painting is more critical than the out side temp.

I would take 75 deg metal temp and 50 deg air temp over
80 deg air temp and 50 deg metal temp any day.

Also, thought of something that may be of interest. There are specialty companies that make a cold weather epoxy for people that paint outdoors.
Would not work in automotive.
Even the so-called cold weather epoxies just plain stop curing when it is too cold..

This is another good reason to use infrared heat in your shop..

OMT
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Old 10-16-2005, 07:11 PM
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So what sort of problems could be expected in a panel that has just been painted with catlyzed urethane, given 24 hours or less exposure to temps above 55F, maybe with some heat lamping, then shoved outside where the weather will continue to hover around freezing for say, about another four months or so?
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Old 10-16-2005, 08:23 PM
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Quote:
Originally Posted by crashtech
So what sort of problems could be expected in a panel that has just been painted with catlyzed urethane, given 24 hours or less exposure to temps above 55F, maybe with some heat lamping, then shoved outside where the weather will continue to hover around freezing for say, about another four months or so?
***********************************************
This is really too simple to answer as a good friend of mine went through this problem last year, Ga winter of course is not as bad as your winter.
He built an addition to shop and new part did not have heat except for the salamander type heater. He did not want to spend the money last winter so no heat at night and shop got up to 70 pretty fast in morning once he fired up the portable heaters.
However if the metal temp on the car is 45 degrees, it will take about 4 hours at 70 degrees to get to around 62 degrees.

Problems encountered:
Of course he had his share of paint lifting and primer mapping while painting but that is no big deal.

I will never forget the first full week of 80+ degree days, he called in a panic
as both dealers he does warranty work for were calling him every-time a customer brought there car in and ask why the paint was dieing.
No big deal, thats what they make buffers for.

About a week or two later his first truck came in, it was a warranty repair before the truck was sold (customer did not know about) now the roof and hood is starting to peel in some areas. (clear was popping from trapped solvent that broke adhesion from base while curing)
Don't think this truck owner was not bent out of shape.

This was the start of the problems back in April, he added an extra painter to do the buffing and bubbling and peel jobs that came in over the next few months.
Is he done yet? No way, he will be getting jobs back for next five years if these people keep their cars.

Tell your boss, heat is cheap!
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Old 10-16-2005, 08:49 PM
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Quote:
Originally Posted by OneMoreTime
Even the so-called cold weather epoxies just plain stop curing when it is too cold..

This is another good reason to use infrared heat in your shop..

OMT
I think you're the one who eased my mind so much when I screwed up making a foam and epoxy egg. A cold snap hit right after I applied some layers of epoxy and fiberglass and the whole thing was just staying sticky. IIRC, you said it would continue setting once it warmed again, and it did.

The nice thing about epoxy is catylizing (is that a word?) is an exothermic reaction. It will start hardening with the heat it produces. If it cools too much before it hardens, though, you have a sticky mess until it gets warm enough to finish hardening.

I can imagine a really bad situation if that stuff doesn't get to cure for the length of an Idaho winter. You probably don't have as much freedom to use faster catalysts with paint as you do with resins used for glue or FRP construction.
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Old 10-16-2005, 10:06 PM
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I've never had to paint under these exact conditions before, so it has me worried. When I worked in Southern California, there was never any issue, but the guys I work with seem to take it pretty lightly and even b***h that I want the shop too warm (58-60F!). Now the comebacks I have seen have been mainly what I deem to be extreme susceptibilty to stone chipping. Also, I've seen areas that have been chipped start to peel easily, even though the surface was very well sanded. Consequently I have been adding a hardener to my basecoats that is recommended by PPG for flexible parts and nose areas of vehicles, hoping this will help mitigate problems. Also I am leaving LOTS of flash time between coats.
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Old 10-30-2005, 05:22 PM
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So it looks like the curing will start back up once the temperatures come back up. I was worried about the temperature drop also after I top coated the car. With the Nason Ful-Thane it says to use the fast reducer while painting in the 50-65 range. It says not to apply it below 50 but says nothing about curing.

Last edited by Scode68; 10-30-2005 at 05:49 PM.
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Old 10-30-2005, 06:12 PM
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I guess this is a problem for a lot of people, including me, these days with winter coming on and I have been a bit confused about this temperature thing. Is there a kind of "rule of thumb" to go by as to how long it takes for a complete cure at a given temperature? What I need to know is how long does a car need to stay within the curing temperature range before it would be safe to move to where it may be cold for weeks or even a couple of months before seeing warm temps again. Heating costs are not the concern here but I can only use the shop for paint on weekends and then I have to move it out before Monday morning. I am more concerned about epoxy and 2k primers at this point because I have yet to start on this one and the top coat will probably come well after warm weather arrives but it would be interesting to know the same info about bc/cc also.
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