anyone have an idea what happened here? the car was shelved for a while and i don’t remember if i coated it with future BUT i took it out finished the decals and sprayed it with the 2 k clear shown. the funny thing is the roof,hood and trunk cracked right away, the sides cracked a day later. as you can see it is cracked right through the decals so i may have used future i just don’t remember. problem is i have a mountain dew buick ready for clear and i used the came tamiya white. i am assuming it is not a reaction with the tamiya since the black also reacted the same way. disreguard the white dots on the 27, they were caused by setting solution left to dry on it. thanks
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Huh. Normally I would say that one clear coat cured at a different rate than the other, but you say the model was on the shelf for a while, so that rules that out. It doesn’t appear that the second clear coat ate through the other. It does appear that the second clear coat caused the first one to crack or shrink. The 2 clear coats are incompatible somehow. Sorry that happened to you. What a shame. For the second car I would use Future rather than the 2K stuff.
wow that sucks. is this a lacquer clear coat? Since future is acrylic this may be the issue.
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My guess, FWIW, is that the cracking is in the topcoat clear, and the issues lie in just the topcoat and have little to do with the original layers or the decals. The outer surface of the clear dried faster than the bottom surface of the same coat. That is, the outer surface dried and shrank creating cracks as it “floated” over the bottom surface which remained somewhat plastic.
Without knowing any more about how the topcoat was actually sprayed, I’d suspect that it was applied too thick (if as a single layer) or the subsequent layers were sprayed without giving the initial layer(s) the correct amount of drying time (either not enough or too much time). Usually, the fine print on rattle cans will specify to spray an initial light coating and either follow that up with subsequent coats after a certain amount of “flash” time, but if that time is exceeded, to wait (often something like 24 hours) before spraying the next coat.
So, I’d say what happened here is that the top surface of the clear trapped solvents in the bottom surface. As the top surface continued to dry and cure, it shrank and contracted over the still soft/plastic bottom layer with the cracks created by the stresses in the shrinkage. So, the entire coating of clear was not applied to become a single homogenous layer from the top surface to the bottom surface but applied so that it became stratified allowing different rates of drying and shrinkage between the top and bottom surfaces.
Everything under the topcoat clear (the original colors and the decals) was incidental to the basic issue with the method of application.
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The good news is that it looks fixable, at least in the photos. Perhaps you decant a little of the 2K and flow it into the cracks with a fine paintbrush. After giving it a few days to cure you could sand smooth using subsequent grades of sandpaper down to 2000 or so. Then hit with a final coat of the same 2K. It’s worth a try. It looks like it’s on so thick you won’t sand down to the decals.
Other good news: I can’t see any decal film. Some folks here might take note of your technique.
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michael the hood was actually cleared once about three weeks prior to this recent clear, i used it as a test before doing the whole body. it did have a couple fine lines in it but i thought it was from when i sanded down the first attempt at painting it. it had a reaction with the primer and paint. when i sprayed that 1st clear coat i sprayed several mist coats about 5 min apart as it says on the can then a wet coat. 3 weeks later i sprayed more clear on it but went with a wet coat and it severely cracked as seen. with the body it was it’s first clear coat. i decanted and sprayed on a mist layer and waited a few minutes. i have to admit i got impatient as i was excited to see a nice shiny body and continued to mist on coats until i had a glossy finish. i always place a box cover over the body as the paint dries to keep dust from settling on the wet paint. do you think it may have trapped gasses under it that attacked the clear? this clear is a 2k clear that does not activate in the can but as it sprays instead. like i said i can’t remember if i had used future on the body/hood before i shelved it but if i had to i would lean towards yes. i used it on a trunk lid of a recent build over the same white paint with no issues.
Joe
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bravo, luckily i am not too concerned about the finish. this is going to be a shelf model and i am not to happy with the build so i used it to test out this clear over the decals. i always have issues with white paint yellowing after clear and hear the 2k clears do not yellow the white paints.
Joe
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it is a 2k clear so i think a urethane base which usually is pretty inert.
Joe
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matt it may well have been a reaction to the fact that the under layer was future and i put the 2k over it. i wish i could remember. i am trying to figure out if this reaction is typical of this combination.
Joe
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Take some scrap plastic and try it again,
make notes of what you do so you can repeat,
or avoid repeating, the process.
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All coatings shrink, and clear gloss coatings shrink more than any other, because there is no internal restraint from pigment. As a result, they depend on adhesion to the substrate to control shrinkage. If the substrate is a flat paint, shrinkage is more controlled because of the relatively rough texture of the flat paint surface. If the substrate is a gloss surface, only a possible chemical bond between the glossy surface and the applied coating is available to control the shrinkage of the new, clear gloss. The better cured the gloss substrate, the less chemical bond is possible. If the substrate and final gloss coating are chemically identical or sufficiently similar, they will chemically bond and the surface coating may not crack. If they are chemically dissimilar, no chemical bonding will occur, and the top coating may shrink enough to crack. That appears to be what happened in this case. However, even if the two clear coats are chemically identical, cracking can occur if the top coating is applied too thickly.
To prevent cracking in a gloss over gloss situation: Use the same gloss coating, top and bottom. Apply the top coat as soon as possible (after decal complete drying and set). Apply the top coat in multiple, thin coats, allowing only enough drying time between coats for all the solvent to flash off (tack free). Keep the final thickness of the top coat to a minimum. If you want more “depth” to the finish, wait until fully cured, then polish the top coat.
Applying clear gloss coats is based on science, but it is still an art. Even with my knowledge and understanding, I dread a final gloss finish. Fortunately, few of my builds require one. My hat’s off to you guys who build cars!
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i am actually in the process of doing that.
Joe
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