Poor adhesion between basecoat and epoxy sealer

bigmoparjeff

bigmoparjeff

New Member
It looks like I have a disaster in the making, so I thought I would post about it here to try to find out what I did wrong and to see if anyone had any tips on remedying the situation.

Here's what I did, in order, with times:

Thursday 12/16 around noon, I mixed up my sealer. White SPI epoxy, reduced 20% with PPG DT870. All components were in the house at 68 degrees F. After sitting for a while you could see it separating, so I would give it a stir every so often whenever I would walk by.

I decided to do a better masking job than originally planned, so it was around 8pm by the time I began spraying on the sealer. Shop temp was 68 degrees when spraying. I set the temp down to 65 and walked away at 9PM.

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Friday 12/17 around 1pm shop temp was brought up to 68, then the heater shut off. I tacked off the epoxy and started spraying base. I was using PPG Shop Line base and it doesn't cover all that well, so I ended up running out of paint. I ran back to the jobber and got another quart. Place is local, so the round trip took less than an hour. Shot on one more coat of base, let it sit for 45 minutes, then applied one fairly heavy coat of clear. I left the shop around 5pm, temp was about 60. I left to visit friends as I usually do on Friday evenings. I returned to the shop at 1am. Temp was in the mid 50's. I turned the heat back on, set to 65, and let it run till Saturday evening at 6pm.

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Everything seemed to be fine. The truck will not be garaged and it will driven in salt, so longevity is the number one priority on this project. The bottom of the cab got a heavy coat of bedliner for protection.

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I managed to get some bedliner overspray on the paint, and when I tried to pick it off, the paint came off of the epoxy instead of the bedliner coming off of the paint. Further experimenting showed that I can choose any spot and scrape the paint off with my fingernail.

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It was very easy to peel the paint off of this piece of masking paper.

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The truck belongs to a friend of mine. It's a project that has gone way beyond the original plan, and I should have never gotten involved with in the first place. Getting the jambs painted and underside coated was to be a huge milestone and a time to celebrate and instead the thought of having to get all the paint back off and redoing it is making me sick.

Any thoughts, suggestions, advice will be greatly appreciated.

Thanks, Jeff
 
Raymond_B said:
I am not a pro, but have a question. Did you by chance take the *metal* temp as well as the air temp?
Click to expand...

No, but the heat was on for hours before any spraying had begun, so I'm sure the cab was up to temp. The heater is very close to where the cab is.

Jeff
 
i would bet that you will eventually gain adhesion. it might be months until that happens but should eventually happen as the solvents come out. with the shop at 60 deg when you shout base and clear, the metal was prob 50deg. you only gave it 45 min for the base to flash. in those temps it would have been best to sit overnight before clear.
 
A friend of mine has a couple infra-red lamps that I could probably borrow over the holiday.

Would it be a good idea to give them a try?

It will be sunny out tomorrow, though temps will only be in the thirties. I'll put it out and see if the surface temp gets up to something reasonable.

Jeff
 
30 mins at metal temp 110 to 125
Each panel.
Also, with that base not covering, you should have waited longer to clear, like the next day.
 
that will help. both sun and the lamps but i think its really not going to gain full adhesion until prob mid summer when that thing can sit out in the summer sun and bake for a few weeks
 
i had a boat transom and name i did some years back. couldnt get it in the building because of the tower so i did it and it was prob 50 out. it all worked out but i had to do a repair 2 years later and when i sanded into it i could still smell the solvents in it. of course that was many layers of base and prob 10 coats of clear.
 
Interesting you kept the heat between 65 and 68. The epoxy generally doesnt like below 65(granted reduced its more forgiving) but the reducer you used is mid temp and for 65-80 degrees. Might help next time to set the heater to like 71 or 72 to give a little margin.
 
Thank you all for the tips and info. I'm feeling better now.

I can't say that I've ever purposely tried to peel off any of my past paint jobs, so I've never been aware of what the bond between the base and primer would normally be. This came about because of the spatters of bedliner getting on the paint, otherwise I wouldn't have gone looking for problems, and I'd be a happy camper. No paint came off when I removed the masking tape, which I didn't do till Monday, so that's probably a good sign.

I do realize the Shop Line is pretty crappy paint, but I figured it would be good enough for the jambs and firewall. I used it on the front bumper cover on my van 10 years ago, and it still looks great, and I've used it on quite a few other vehicles without any issues. I wont be doing the exterior paint on the truck, so it will be up to whomever does to decide what brand of paint to use. My job is to fix the rust and put it back together. It just seemed like a good idea to do the jambs and firewall while it was still all apart.

Jeff
 
Barry said:
30 mins at metal temp 110 to 125
Each panel.
Also, with that base not covering, you should have waited longer to clear, like the next day.
Click to expand...
I'll give the infra-red lamps a try.

This was the worst covering base that I've ever used. Don't know if they have changed the formula lately or if it's more related to this color. I often have Shop Line mixed up single stage because I'm doing spot work on older cars and that seems a bit better. I will keep your advice in mind next time I'm using a clear coat.

Thanks, Jeff
 
BoostedOne said:
Interesting you kept the heat between 65 and 68. The epoxy generally doesnt like below 65(granted reduced its more forgiving) but the reducer you used is mid temp and for 65-80 degrees. Might help next time to set the heater to like 71 or 72 to give a little margin.
Click to expand...

The only reason I payed so much attention to the heat is because the instructions for the epoxy said to stay at 65 or higher. I also assumed that there would be a little wiggle room in that 65 degree limit, so I didn't think there was a need to go any higher. It takes a lot of oil to keep the shop warm when the temps are cold outside. The truck cab is between the heater and the thermostat, so the cab itself is probably 3 to 5 degrees warmer than what the thermostat is reading.

Most of the stuff I do is small areas, or single panels, so I rarely use epoxy on them and haven't had to pay much attention to temps in the past. For anything bigger than a partial panel I normally paint it outside. I've painted quite a few things in temps as low as the high 30's that have held up fine over the years.

Jeff
 
Here's a screenshot (could not figure out how to cut/paste the pdf) of page 13 of the SPI Tech Manual, a link to which is in my sig

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I am starting to think there should be something in there about the difference between air temps and surface temps, but the epoxy entry is already getting pretty long as it is.
 
I've had Shopline peel off the epoxy sealer when doing a 2 tone. I have seen tape tracks with other bases, but never had any other base peel. This was during the summer, so definitely not a temperature issue.
 
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