Building with epoxy?

  • Thread starter Professionalamateur
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Professionalamateur

I have a 71 Mustang coupe that I am trying to make straight without filler. I took a metal shrinking class four years ago and I feel I picked up the hammer/ dolly concept fairly well too. Unfortunately most of the small sections I have been working on were previously hit with an aggressive grinder and filled. The unlikeness in metal thickness does not allow the shrinking disc to work as well as it should so I'm limited to mostly hammer/dolly for these parts.

I've noticed a few of the veteran posters here have stated that they use epoxy instead of 2K. I was wondering if there are any potential issues with doing some build with epoxy. I planned on shooting epoxy and basically just blocking it all the way down and repeating. I don't have an issue with using 2k it just seems logical to have the foundation as close to straight as possible. This is going to take years for me to get right so extra curing time or extra effort is not an issue. I'm not concerned with "wasting" some product either. I'm not the least bit concerned with sanding off a couple hundred dollars of product if need be to get this right as this is the only car I will ever build for myself and I will never sell it.

So what are your thoughts?
 
it is how i do it. i use a 2.2 gun and do one heavy coat at a time . i do let the mixed epoxy set overnight before shooting .
 
It takes more cure time using epoxy as a surfacer compared to products like poly primer but it is a more durable product, if you have the time it's a good way to go for sure.
 
Lately, any time I try to spray a "heavy" coat of epoxy, it ends up looking like swiss cheese. I use a 1.4 tip and spray it the same as anything else. SPI epoxy works great for the application you describe.

What's the trick to not spraying swiss cheese Shine?
 
stand on one leg , tilt your head to the left and smile.........................

i use a big gun , vaper 2.2 . i do not reduce , i let it set overnite , i shoot a wet double coat . double coat is like old enamel . you go down the door then back up it . just depends on how it looks. had no problems doing this so far. epoxy block.jpg

epoxy 1.jpg
 
I'll be watching for the answer to that one, Strum.
I just remind myself when it comes out like that... I intended to block the top 1/3 of that coat off anyway and start cutting.

Shine, you beat me to it... Got it! I'm not smiling big enough:highly_amused:
 
shoot everything like it is a coat of clear. improves your gun handling and saves you time . too many people shoot primer and dont pay attention like when shooting clear .
 
Wow that was quick! The product sheets refer to inducing or induction time so I assume that's what you're referring to Shine when you say to let it set over night. Bob how long should I wait before blocking or re shooting a section if I lay the epoxy a little thick? I sprayed a small section last weekend to experiment with how it sands and did get a section of swiss cheese mid panel. I'm using a used Sata klc 1.4 I just picked up and haven't dialed it in yet. I upped the air pressure and it seemed to behave.

Thank you all for your input!
 
How long to wait for sanding-there's a lot of variables... temps, application thickness-a lot of things will affect the rate of cure. Next time you shoot something also shoot 4 test panels and let them cure, sand one at 1 week, the next at two weeks cure, the next at 3 weeks cure, and the last at 4 weeks cure. You will see a difference in hardness and how they sand and that tells me something. You might reach full cure at 2 weeks in your environment or if it's seen time in the sun. Now, does this mean you need to wait 2 or 3 or 4 weeks before sanding?-no If it's cured well enough to sand you might as well start the cutting and what's left on will stabilize-finish curing because in reality the shrinkage won't be much. Cut off what isn't needed, reprime and repeat. Before the last round of sanding I usually let the parts set a few weeks or more, the final blocking shows me if any shrinkage has taken place and how it sands tells me how well it's cured. You'll get a feel for how well the epoxy is cured after you've played with it some. This is just my opinion, others might think differently and it's a good topic to discuss for sure. I also think most urethane clears usually don't reach full cure for at least a month, others will disagree, and doesn't mean one has to wait a month to color sand and buff but for the final polish I think it's wise to go over it again when full cure is reached, the product is then stable and hardened.
 
there are these poly plastic parts i spray that have a leathery texture in them. i use the epoxy on them to build up and sand smooth. its by far the best way. for the past year though i have had even better success by mixing my epoxy and adding fumed silica filler to it. basically a filler used to thicken resins to make putty and other things. its funny it completely changes how the epoxy sprays. you can hammer it on and have no swiss cheese effect, runs or shrinking down the road. the stuff i have is a bit coarse to be putting in a sprayable primer but it does work fantastic and sand-ability is even better. i dont really know why i am telling everyone this as i dont really recommend anyone going out experimenting with the epoxy on their high end resto but the epoxy is really nice with a slight amt of filler added. its so much more user friendly to spray. i havent found and negatives to it as of yet and like i said i have been using this method over a year now.
 
Interesting, awhile back I thought about ordering some glass micro spheres to try as a filler material but I think Barry already did some testing and it didn't work out. I bet the filler ratio is key to keeping the durability and flexibility of the epoxy good.
 
Probably. I dont do any kind of measuring. I add just enough to give it a slight amt of body to it. Im sure the type of filler added makes the biggest difference. Microsoheres you make a light weight and easy to sand product but you lose strength. Silica is middle of the road. Each filler has its own properties.
 
We use three different micro-pheres as you guys call them, three kinds in our Turbo primer and one kind in out regular and high build primer.

I have done a lot of test with them in the epoxy and it does not make the product better, a little does nothing but when you use enough to make the epoxy fill more, it goes down hill fast.
 
I've been using epoxy only for years also.

I usually do one med/wet coat in the morning, one really wet coat at lunch, and one more really wet coat at the end of the day using an Iwata 1.5 tip

I get swiss cheese primer if I dump a quick wet coat 1st. Always have. Guys I've turned the product on to say the same thing if I don't tell them.

I let the panels sit at least 1 week before blocking and set in the hot sun as much as possible. I get good build from 3 coats and occasionally do 4 coats and get great build.

Maybe the 2.2 tip has something to do with it?
 
Great info from all of you. My car is currently stuck on a lift so It can't get any sun exposure. I'll wait to do the major stuff until its mobile again and I can move it outside.

At what point is an area too low to fill this way. I've heard that high fill primer is good to 1/16" , but is that a production shop guideline because it is not given time to fully cure?

Thank you all for your input.
 
imo you really shouldnt use primer to do bodywork. a 1/16" can prob be done but i would not do it. whats the point really. a little skin of glaze takes 10min and wont shrink. primer would take you a day or two to get that much down. only primer i would ever consider putting on kinda heavy would be polyester and even that i try to remove as much as possible. keep primers and paint as thin as you can.
 
Thanks Jim. I worded that poorly. I was actually inquiring how thick a small spot of epoxy could be applied over time if allowed to cure . Most of what I'm dealing with at the moment are low spots the thickness of 1-2 sheets of paper, however one small spot that was welded has a depression.
 
well epoxy is a structural product/plastic when its cured meaning it does have strength without adding anything to it like fiberglass etc. sooo, you can have a solid chunk of epoxy thats 2" think and its fine but the kicker is in our industry we spray it so it has to have solvents in it to thin it out. what i am getting at is if you apply the epoxy slow enough to get all the solvents out you can put a hell of a build down with out problems. might take you forever to do it though. if doing real high build like that, 2 coats a day is where i would keep it. alot of flash in between. a few hours atleast..
 
Based on input I will to shoot one coat in the morning and another in the afternoon, then let it sit for a few weeks before blocking.
 
When it comes time to sand you'll probably be impressed to see it fills more than you expected.
 
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