Epoxy: High Film Builds

crashtech

crashtech

Combo Man & Mod
I have been using epoxy as a surfacer on some of my jobs. This is, so far, an "off label" usage. As far as I know, SPI has not done any testing on the long-term durability of high epoxy film builds.

I have some jobs with 4-5 primer sessions of two coats, each 2 to 7 days apart. They are blocked out in between, but some low spots are holding most of the primer. Conceivably there could be close to 10 coats of primer in some areas, usually in factory waves near edges of panels, though we always sand off the excess right on the edges to increase chip resistance.

Has anyone experienced problems with high film builds?

Barry, if there was to be a problem, what would we look for? Do you think it could crack in a few years?
 
There is no downside to what you are doing, other then extra work.

The SPI epoxy is flexible at 1/2 inch thick and has less shrinkage per mil of build then any other product we make.
 
i try not to leave excessive build where it is not needed. such as peaks , edges and valleys . i have a hockey puck from the 57 vette that is still flexible.
 
I feel like I am doing right by my customers by spending the extra time to use epoxy only on my restoration work, but it made me a little nervous using the epoxy in a way that is not officially recommended by SPI.

It would be great to see the tech sheet amended to include use as a sandable surfacer for blocking.
 
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Crash, I've had good results with build like you are describing as long as it's applied in stages like you've been doing there will be no problems-it is very stable. I do like polyprimer for the majority of my blocking, starting with epoxy and ending with epoxy before paint has proven to be the best for no shrinkage and durability. My Son's car was a testbed for epoxy abuse on a few panels-there have been no failures or hints of any problems of any kind.
 
Bob, could you please describe to us this testbed for epoxy abuse?
 
LOL, My Son's car had some serious roof and decklid damage that was corrected mostly with epoxy primer, major pitting and mellow waves and I would bet the decklid had 12+ coats of epoxy-(it was the panel we emptied the gun on whenever there was left overs). There was cure time between applications, and I had thought about just replacing the decklid so I really didn't care to much what the outcome was from bombing it with epoxy, I was amazed during the sandings just how stable the epoxy was and we saved the part. To this day there is no shrinkage or any hint of repair or failure even after four summers in the sun-this is not a garage kept car, UV resistance in the clear has been excellent and the whole package is very chip resistant. I wouldn't hesitate to use epoxy as a surfacer start to finish if you have the time to let it cure good between applications-this is the only drawback to epoxy primers-they are a slow cure product initially but very stable once full cure is reached.
 
WOW!!! I had no idea you did that but was a pretty safe bet the way you let it set, if you ever need to get a new deck lid because of epoxy failure, let us know, I will buy new one so I can have the old one to test.

I love it!!!
 
I feel better now. Bob , that sounds even more extreme than what I am doing. Nice to know it is holding up for you!
 
Barryk;1170 said:
WOW!!! I had no idea you did that but was a pretty safe bet the way you let it set, if you ever need to get a new deck lid because of epoxy failure, let us know, I will buy new one so I can have the old one to test.

I love it!!!
Click to expand...

Barry, I bet the epoxied decklid will last a lifetime+ Some of the stuff I've been doing with this product and a few others isn't textbook but having only positive results.
 
Another quick question?

How long does it take, for Barry's epoxy to fully cure?
 
Can't answer that question as varies.

Full cure could be 30 days to six months under paint, depends on way to many factors to guess.
 
So in reality, Barry.
Your saying it cures at approximately at that same rate as clear (I do understand, there are so many variables to figure into in the total cure equation)
 
Full cure. It depends on a lot of variables, temperatures, application thickness and time between coats. Anything with a 7 day recoat window you know hasn't fully cured in a week, two weeks-probably ok if the application was right and good temps, a month-definately completely cured IMO if application was good and temps were maintained-I think some time in sun also helps. Thing to remember about epoxy is any shrinkage happens fairly early within the 1-2 week range and it becomes stable even if full cure isn't reached for 30 days the shrinkage at that point if any is very minor. Do some bench testing and you'll see how and when the shrinkage stops.
 
I used a lot of Epoxy Primer a couple of years ago when I did the Blue Mustang Convert that is in the tech book. I was determined that I was not going to use filler on that job, and had read a lot of what Shine was doing with Vettes and epoxy. That meant that I had a lot of metal working and even more priming and blocking than I usually do. I allowed a minimum of a week between the application of 2-3 coats of epoxy and the blocking. I start my blocking with 80 grit, and the sanding marks have not shown up, so it must not be shrinking.

I now have 2 cars in the garage because of the Mustang project, so it must have worked pretty good.

Aaron
 
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