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Old 12-05-2015, 12:24 AM   #1
Mini-Skoolie
 
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need help figuring out why my paint failed

I have had a major paint failure and it is boggling my mind. please give me your input if you have any ideas as to why this happened.

i painted over my original school bus yellow with a tractor paint of some kind years ago, it held up great.

then years later, i sprayed a coat of Miller equipment enamel, it held up great for years, but faded quite a bit,

I just put a fresh coat on my bus this summer. over the top of the enamel, i used a clear coat/uv protectant/ hardener called break through by ppg. i sprayed the paint and clear coat. it was august in idaho, warm and dry. i allowed days in between application. everything was perfect..... and then....

just last week i had my bus in the shop. some time between dropping it off and picking it up, this happened:

somehow the paint lifted in a couple spots. whats really crazy is that it lifted past all the previous layers of paint, lifting the original paint all the way to the metal.

it was a heated shop, my first thought was it was directly under a heater for some time and then moved out into 20 degree temp. but the bay that my bus was in doesn't have a heater over it.

there was nothing that came in contact with my bus....liquid, solid etc....

there were a few spots where i didn't feather sand the edge of the existing paint quite enough before spraying, but for this to happen?

if anyone has any ideas please share. thanks
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Old 12-05-2015, 08:40 AM   #2
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I'm thinkin' paints were not compatible? Not all paints work together, they can attack each other...you'll get fish eyes, orange peel etc.
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Old 12-05-2015, 09:28 AM   #3
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idk, but as a guess, i think thats from contracting and expansion of the metal. too many layers contracting or expanding at different rates.

my 2 cents
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Old 12-05-2015, 09:56 AM   #4
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Was the first paint or clear coat an acrylic? Enamels, as a rule of thumb, react differently over acrylics than acrylics over enamels
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Old 12-05-2015, 11:29 AM   #5
Mini-Skoolie
 
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it just seems odd that those two paints would sit together for years with no problems. i can't remember what the first layer of paint was. but that first layer sat under the enamel for years. and this second layer of enamel sat on top of all that for months. i would think that if paints were going to react, they'd do so within the cure time of the paint.
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Old 12-05-2015, 11:30 AM   #6
Mini-Skoolie
 
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.....also there was no clear coat under any paint, just on top of the second layer of enamel.
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Old 12-05-2015, 11:36 AM   #7
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I read your initial post, but the pictures make it look like you painted over galvanized sheet metal. Or perhaps the previous paint was a silver colour? Or the peeling pulled back all layers of the paint to expose galvanized? IDK..

I'm just wondering because the peeling would make perfect sense if the paint was layered over un-prepped galvanized steel..

Probably not, but it's worth ruling out some more options...
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Old 12-05-2015, 03:34 PM   #8
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Paint and galvanized dont get along well. It doesnt look like the steel was prepped correctly.
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Old 12-05-2015, 04:00 PM   #9
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that is the original bus body you're seeing there, not a paint. the peeling pulled off original 1986 bus yellow paint. thats what racks my brain, school bus paint is bomber.
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Old 12-05-2015, 04:13 PM   #10
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Guess I've never seen factory steel being galvanized.
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