Scared of primer shrinkage

M

mark kestler

First post guys, but long time reader.

A little backstory. Restored a 1966 nova ss. black epoxy over bare metal, body work, 2 k primer, blocked and blocked and blocked, sealed then base and clear. Used spi epoxy, spi 2k regular primer, spi sealer, matrix base and spi univ clear. We probably didn't let the primer sit/cure long enough as we blocked it the next day after final prime then based and cleared. car was straight after painting. waited a week and wet sanded and buffed. looked amazing. 3 months later, there were a few rings/areas in both quarters that weren't there before. we again wet sanded and buffed and got the majority out but is still a little noticeable to me but I'm happy with it.

I'm now ready to paint/primer my 72 corvette. I'm thinking that the issues with the nova were related to us not letting the 2k primer sit/cure long enough before final blocking. we did not sit it in the sun and was in a temperature controlled garage the entire time painting. My father in law has noticed some primer shrinkage as well with SPI 2k on a car he;s doing now. now he has not been letting it sit either. just shooting primer, next day blocking, then noticing areas a few days later.

What is a way to prevent this primer from shrinking or what is the required time that I should wait for the primer to cure.

My plan with the vette is to spi epoxy over bare glass. then do my body work over the epoxy and when happy, re apply epoxy over the body work to seal. then I plan on the SPI 2k but should I spray the primer and wait a week or what do you guys do. Paint store who sells SPI, one guy loves it, one says it shrinks if you don't give it time. What is the appropriate time. Another thought is, should I skip the 2k and just use epoxy and block that. Should I use polyester primer. the body is pretty straight so I don't think I need the filling ability of polyester.

Looking for opinions to prevent shrinkage over time or just use epoxy for it all. Sorry for the long winded post. used the search bar just for those who like to say that first.
 
For a show car finish not to shrink a tiny bit later, I wait a week after priming.
But beware, some 2K's get really hard and difficult to sand that long later.
90% of that shrinkage can be gone waiting just 2 days after spraying.
Most people never notice a small bit of shrinkage later, it usually takes a couple months
out in the summer sun to get it. Unless you have a really slick finish you won't even see it.
But at car shows most people I ask admit to rebuffing their car a year later because it shrunk down a tad.
Even with epoxy there is some shrinkage.
 
also remember when you put the base on that solvents sink into the primer. once you put the base on be sure to let that sit 12-24 hrs before you clear. if not the primer will eventually shrink back down as the base solvents come out.
 
Thank you all for the responses. I'm not looking for a show car finish so much but I dont what the corvettes seam lines showing where I filled with fibertech. I like the idea of polyester primer for the lower chance of shrinking, but can poly be sanded fine enough to get out all the scratch Mark's before applying spi epoxy as a sealer. Also I dont want to mess my lines and edges up with too thick of poly either. If I went epoxy only, would I epoxy my bare glass, body work, 2 coats of epoxy, block, fix any issues and then reapply and block until I'm happy. How do you guys make a final decision on what to do/use. Appears there's a million ways to prep one car
 
I personally prefer all epoxy and have been very pleased doing it the way you are describing. Do remember though, the epoxy will not build as fast as the 2K. I usually shoot 3-4 coats with an hour or two of flash between coats. Also, focus your attention on your filler work. By the time you are ready to primer, the car should be pretty dog gone straight. Using primer to correct bad body work always leaves a lot to be desired.

Good luck with it. I think you will be impressed with what the SPI Epoxy will do.

John
 
I appreciate all yalls input and now I know what direction to head.
 
As @Jim C says, simply waiting overnight to apply clear also gives more time for those solvents to get out. That's a trick we're able to do quite often even on everyday work sometimes, when we want the job to look nice. It's especially helpful if the 2K is fairly fresh, since fresh 2K will absorb solvent a little more readily than fully cured 2K.
 
your seams are likely to ghost back anyway unless you glassed them or used VPA . if your straight enough to not need poly then use epoxy only . you'll get 0 shrinkage and a far better job .
 
Lately on my "daily driver" type work I've been using epoxy. It takes an extra day, but screw it. If its a sunny day. Ill prime and pull the car out and let the sun to its thing. Plus it seems to really prevent the edge mapping issue that you normally see with a 2k primer.
 
Those rings you are referring to may have been when you blocked the 2k down to filler,then sealed and painted. I always try to lay down a final unreduced epoxy coat or 2k primer coat for finish sanding. If you block thru that all over the car with 400 or 600 you weren't ready for paint.Reduced sealer coat is only an adhesion coat.
 
I was planning on doing all epoxy on my project. But, I've run out of summer weather tempuratures. I bought some turbo 2k to hopefully speed up the process, and not have to worry about running the heaters un-attended all night. After reading this, I'm doubting that decision. Currently, I'm only getting a few hours a day above 65 degrees.

Though, the OP said he used regular 2k, hopefully a couple coats of epoxy, and turbo 2k will hide my filler sins.
 
I think another reason I seen some areas after the car sat was when blocking, if there was a low spot, we may have put the primer on thicker trying to fill it in. I think that after the cure time, it all shrunk, but thicker areas of primer were more noticeable. I just rushed it and wish I would have let the car sit in primer. On the vette, I'm going to try blocking with epoxy and if not, its 2k and letting it cure. Here's a pic of the car when we got it and a little under a year later. Not bad I guess for a first full restoration. Only thing that made it better was that me my dad and father in law did it all ourselves from metal work, paint, interior. Only thing we didn't do was the alignment
 

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Two questions here; I noted the comments on waiting at least 24 hours before applying clear over base. However, I'm using PPG Concept metallic blue and the PPG rep was adamant that the clear must be applied within a six hour window after the base. Also, I'm well aware of the 65 degree minimum cure temperature for epoxy, but is there a minimum temp for the high build primer?
 
epoxies are more temp sensitive than urethanes. epoxy really starts slowing down under 65. you can apply it but the colder it is the slower it will go down to about 50deg where it will just about completely stop. urethanes like the 2k and clearcoat keep above 50-55. i have not used ppg base but when the companies give you recoat windows, they are all full of $hit. 6 hours is what they tell production shops so they can get the stuff out of the shop quickly and at 6 hrs that allows a huge margin of error for a painter that has no idea what they are doing or crazy environmental conditions. base is just an air dry product. no crosslinking occures so there is no reason your clear wont bite into that base when its 12-24 hrs old assuming its not dry sprayed or anything like that.
 
Two questions here; I noted the comments on waiting at least 24 hours before applying clear over base. However, I'm using PPG Concept metallic blue and the PPG rep was adamant that the clear must be applied within a six hour window after the base. Also, I'm well aware of the 65 degree minimum cure temperature for epoxy, but is there a minimum temp for the high build primer?
Their clear, their base I assume. First bc/cc I used was Nason, and that clear was so thin it just completed the base, took three wet coats before the color actually came out and consistent. Overnight is more of the norm, which is finish basing a car before you leave, then next day you clear, so usually within 24 hours. I am assuming that PPG got blamed for alot of clear delaminating and flaking off.
 
Two questions here; I noted the comments on waiting at least 24 hours before applying clear over base. However, I'm using PPG Concept metallic blue and the PPG rep was adamant that the clear must be applied within a six hour window after the base. Also, I'm well aware of the 65 degree minimum cure temperature for epoxy, but is there a minimum temp for the high build primer?
PPG Concept is not a base, its SS
 
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