Do you still get a chemical bond after sanding ......

I'm no expert, just someone who does this for a living. I have enough of my own personal anecdotal evidence to suggest that sanding can indeed improve the adhesion of epoxy even within the window, particularly in the context of filler application. I'm going to keep doing it, YMMV.
 
i sand as well. not really if the epoxy is a day or two old but much beyond that and i will scuff it with some 180 before filler. i have had too many instances where epoxy gets to the 4-7 day part of the window and if i feather out the filler i can scrape the edge of the filler off the epoxy with my fingernail. i see a definite difference in adhesion of products stuck to epoxy the longer it sits beyond 72 hrs in summer temps. epoxy is a great thing but for me i will not put anything on it beyond the 48-72 hr mark. i work on it somewhat fresh. the longer is cures the more chemical resistant that stuff gets. i have personally never been able to figure out why the tech sheet gives a 7 day window. imo window should be 72 hrs in summer.
 
Yeah Jim C. I also do same. If it's 4 days old I always sand before applying anything else. Helps me sleep better lol.
 
I’m just gonna make a wild guess that the guy who formulated and actually makes the stuff has the testing and data to know it’s good for at least 7 days, and that 7 day number might even be conservative.
 
Lizer said:
I’m just gonna make a wild guess that the guy who formulated and actually makes the stuff has the testing and data to know it’s good for at least 7 days, and that 7 day number might even be conservative.
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I have no doubt Barry knows his product has an open window of 7 days. I also bet he knows what temperature that 7 day window is good for

Taking a guess, I'd say open window of 7 days at 70 degrees, no direct sunlight.
 
MJM said:
I have no doubt Barry knows his product has an open window of 7 days. I also bet he knows what temperature that 7 day window is good for

Taking a guess, I'd say open window of 7 days at 70 degrees, no direct sunlight.
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Barry has said temperature is not much of a factor. UV light is. The window is actually longer than 7 days according to Barry, but like Lizer alluded to 7 days is the conservative safe guideline.
 
The two
MJM said:
I have no doubt Barry knows his product has an open window of 7 days. I also bet he knows what temperature that 7 day window is good for

Taking a guess, I'd say open window of 7 days at 70 degrees, no direct sunlight.
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The two things that accelerate the open window are UV and infrared radiation, not temperature. To that end, If I know I will not be able to keep it above 65 for 24 hrs I push the part into the sun for at least three hours or put it under my infrared lamp for 30-60 min.

All that said, I still prefer to get things on epoxy earlier than later. Every day waited is one more day marched to the end of the open period. And chemistry or biological reactions do not progress stepwise, they are linear. Meaning the epoxy is not going to magically and suddenly change on day 7. It is a gradual progression to that point.
 
Temperature certainly has an effect on the curing speed of epoxy, and therefore it might be hasty to assert that temperature has no effect on the 7 day window.
 
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Lizer said:
The two

The two things that accelerate the open window are UV and infrared radiation, not temperature. To that end, If I know I will not be able to keep it above 65 for 24 hrs I push the part into the sun for at least three hours or put it under my infrared lamp for 30-60 min.

All that said, I still prefer to get things on epoxy earlier than later. Every day waited is one more day marched to the end of the open period. And chemistry or biological reactions do not progress stepwise, they are linear. Meaning the epoxy is not going to magically and suddenly change on day 7. It is a gradual progression to that point.
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Now I'm really confused with regards to temperature. So temperature only comes into play with epoxy when it's below 65 and too cold? When it's 90 degrees out, that hot temperature is not a factor that comes into play with epoxy?
 
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all chemical reactions speed up as temps go up so to say it doesn't change the cure rate is nonsense. it might be more correct to ask at what rate does the epoxy cure at different temps. maybe the difference in cure rate is negligible from say 70 to 90. its not really what i have found to be the case but you never know since as i said i am very conservative on those recoat windows.
 
Jim C said:
all chemical reactions speed up as temps go up so to say it doesn't change the cure rate is nonsense. it might be more correct to ask at what rate does the epoxy cure at different temps. maybe the difference in cure rate is negligible from say 70 to 90.
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All I know is what Barry said when I've asked him about it. He seemed pretty sure when he told me that heat (temps above the min) didn't affect it to an appreciable degree. Said it behaves nothing like any urethanes. Goes against what we all have learned doing this, but I trust the man.
 
MJM said:
Now I'm really confused with regards to temperature. So temperature only comes into play with epoxy when it's below 65 and too cold? When it's 90 degrees out, that hot temperature is not a factor that comes into play with epoxy?
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To some extent. If the surface is too hot it can actually “burn” the epoxy and the epoxy will dry real crumbly (experienced this myself).

If you want epoxy to spray better and make it as fool proof as possible then you would actually heat the can to 90 degrees on a hot plate. Myself, especially on a cool day, will induce my epoxy and set the mix cup out on the asphalt driveway in the sun to get real warm.

The complicated chemistry of the epoxy comes down to the alcohols, which is where the issues come from with cold sensitivity. It is not like urethane chemistry and in my numerous conversations with Barry over the last 14 years I’ve gathered that his epoxy with its alcohol is also a very unique formulation.

Also, the “open window” is different than curing or the cure time. Epoxy takes about 90 days to fully cure.
 
Lizer said:
To some extent. If the surface is too hot it can actually “burn” the epoxy and the epoxy will dry real crumbly (experienced this myself).

If you want epoxy to spray better and make it as fool proof as possible then you would actually heat the can to 90 degrees on a hot plate. Myself, especially on a cool day, will induce my epoxy and set the mix cup out on the asphalt driveway in the sun to get real warm.

The complicated chemistry of the epoxy comes down to the alcohols, which is where the issues come from with cold sensitivity. It is not like urethane chemistry and in my numerous conversations with Barry over the last 14 years I’ve gathered that his epoxy with its alcohol is also a very unique formulation.

Also, the “open window” is different than curing or the cure time. Epoxy takes about 90 days to fully cure.
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. So if the temperature is too hot it's causes the epoxy during the curing process to dry out and crumble. At what temperature did that happen to you?
 
Lizer said:
Also, the “open window” is different than curing or the cure time. Epoxy takes about 90 days to fully cure.
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So during the open window of 7 days, the epoxy has not started the curing process?
 
MJM said:
So during the open window of 7 days, the epoxy has not started the curing process?
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No it's curing, but open time and cure time is different. Epoxy that is not exposed to UV light is not fully cured for 90 days or thereabouts. The open window to recoat with filler, more epoxy, etc is much shorter.
 
Chris_Hamilton said:
No it's curing, but open time and cure time is different. Epoxy that is not exposed to UV light is not fully cured for 90 days or thereabouts. The open window to recoat with filler, more epoxy, etc is much shorter.
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Understood, good explanation.

Another scenario for the topic at hand with a vehicle being worked on in a shop or garage that isn't getting direct sunlight.

Epoxy has been sprayed, 48 hours later polyester primer is sprayed over the epoxy. Will the fully cured time be much greater that the 90 day or there about since the epoxy was covered not allowing the open elements (air) to help cure the epoxy?
 
MJM said:
. So if the temperature is too hot it's causes the epoxy during the curing process to dry out and crumble. At what temperature did that happen to you?
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It happens right away, within a few hours. I don’t know what the panel temperature was; it was very hot and in direct sunlight. This was on an aluminum camper I painted. It had to be painted outside. After that, I would spray earlier in the morning before the metal heated up too much.

If it’s too hot to lay your hand on it’s too hot to spray.
 
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