Weird clear/base adhesion problem

V

Vanishingpoint

I did a repaint on my 1973 240Z In December of 2007 and sprayed the sealer, base and clear on the 27th. According to the online almanac the temps were about 75 here in Florida. I used SPI epoxy over the bare metal repairs. then filler work. Then more epoxy to cover any burn throughs. Then I used Turbo 2K primer. I blocked the entire car and then sealed it with white epoxy primer. I can’t remember the exact amount of reduction but I know I reduced it. I then sprayed two or three coats of activated SPI red base. I can’t remember for sure. I then cleared it with Universal Clear. I used 885 reducer. I followed all of the recommended flash times.

I noticed the problem with the adhesion right away when I did a repair on the dog leg area. The masking tape pulled up a little clear with some base in it. I talked to Barry and we both agreed that it may have been a little dry in that area. The car looked great and buffed fine so I wasn’t worried. The car is my daily driver. I noticed that it seemed to be really easy to chip. Wherever I got a chip the clear would then start peeling away from the base getting larger over time. I knew I was going to be spraying it again at some point so none of this was a problem.

So now it’s time for the respray and I’m trying to get to the bottom (if I can) of what I did wrong. Nows when things get weird! I washed the car this morning so I could markup the few rust areas I was going to fix. After it dried I was looking it over and decided to do a tape test on the clear. I put a strip of masking tape down on the cowl and when I removed it the clear separated from the base. I then got some 2” wide tape and proceeded to pull 3 24” long strips from the top of the fender. At that point I had a few more thing to do in the shop so I left the car outside in the 95 degree sun. I decided I should do a pull from the side of the fender to see if I had a dry base issue. Sure enough the clear stuck like... clear and no matter what I did it wouldn’t pull any clear. Then I went right next to the place where I was pulling on the top of the fender and it wouldn’t pull either. So when the paint got hot the adhesion was fine.
That was yesterday. This morning I came in and tried the same test. I put a strip of tape down on the cowl right next to the area that I pulled yesterday and the clear wouldn’t budge. I then went to the fender and it was the same thing. wouldn’t pull any clear.
It seems temperature/moisture affects the adhesion. Yesterday I did half the hood and it was splitting between the coats of base. This morning I tried some of the other half and it puled clear only.
Not sure if anyone has any ideas on this or not. At this point it may be just one of those things. On the plus side stripping the clear with tape is a lot cleaner than sanding :)

Thanks
Derek
 
If I understand you right, one day you can pull the paint of with tape and then next day it won't?? Is this right next to the spot you pulled it off the day before? (Could be telling story)

Also, when you find a piece that does pull off, do a smell test right away as you have about 10 seconds only and see if we can smell any solvents.

Not sure the deal but we will try and figure this out.

Is it more likely to pull off in sun?
Next time a piece does not pull off, put fresh tape over that spot and leave it for 24 hours and then pull off and see if it pulls paint off.
 
Hi Barry
I was talking to a friend yesterday who also uses your products and I mentioned to him that " It kind of smells like solvent when I smell the tape" I figured it had something to do with the friction created when it's pulled. Can solvent be trapped since 2007? The car is in the sun at least 4 or 5 days a week.

It seems to be affected by temperature and possibly humidity.
here is the time line.
8:00 AM wash car and dry
9:00 AM first tape test. Tape pulls clear only on cowl and fender top. Car is in shade at this point.
12:30 PM Car has been in sun since 11:00. Try to recreate the test but can't get any clear to pull. This is in areas right next to the prior spots. I can get a little to pull if I overlap the tape into previously pulled areas but it pulls base along with it.
1:00 PM Bring hood into (slightly) air conditioned shop. Temp in shop is about 82 degrees. Let hood cool for an hour or so. Remove half of the clear from the hood using tape. This time it pulls clear and half the base.
6:00 AM the next morning. Temp around 70 degrees. Tape the other half of the hood and it removes clear only.

On the previous paint job 10 days passed from when I sprayed the 2K primer and I sealed with the epoxy.

Thanks
Derek
 
This is weird, but it definitely sounds like solvent in base and I would say a minor amount, that is why it has lasted this long.

Here again, we are guessing but everything you say points to solvent in first coat of base.
 
This may be far fetched but in my mind there may be solvent trapped and depending on the heat and humidity it migrates between the layers.

When I got through composing the first post I almost didn't send it as this is so goofy there will never be a definitive "this is what you did wrong" moment.

Thanks
Derek
 
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