Mini cracks in fresh paint (Rustoleum spray can painting cast iron part)


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Old 02-16-18, 08:21 PM
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Mini cracks in fresh paint (Rustoleum spray can painting cast iron part)

I'm having to replace the back-pressure regulator for my deep well jet pump. I can save a bit by replacing only the damaged or worn components, so I won't be replacing the cast iron bonnet that houses the spring. I de-rusted it with electrolysis:
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I don't have a pic of the lustrous results, but it worked well. I then scraped the remaining paint off and hit it with a wire wheel and cleaned it with mineral spirits to prep for paint.

I used Rustoleum 285011 universal bonding primer - 2 coats within a few minutes of each other as instructed. I waited an hour before applying Rustoleum 7779 gloss protective enamel. I did several coats spaced a few minutes apart, but I believe I used the spray can too close to the part, so the coats may be a little heavier than they should be.

It hasn't been long, but it has some white primer showing through the black on the vertical surfaces. Will these cracks get worse or shorten the lifespan of this coat and subsequent coats, or can I just add another coat after this has cured to fill the cracks?
 
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Last edited by PJmax; 02-16-18 at 08:30 PM. Reason: added enlarged pic
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Old 02-16-18, 08:31 PM
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Not the painting pro but it looks like the paint crazed.
A reaction between paints maybe.
 
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Old 02-16-18, 08:45 PM
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Okay, thanks. I didn't know about "crazing."
From the source I've just looked at, "Although a craze is a physical surface depression, it does not pose any long-term stability issues to the painting." So, it just won't be as pretty, but that's acceptable. I'm just glad I won't have to strip it off and start over.
 
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Old 02-17-18, 02:52 AM
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It should be fine. It may have been better to have waited a little longer before applying the finish coat but it's not a big deal. No need to start over! IF you were concerned about looks you'd just need to sand lightly and apply another coat of finish.
 
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Old 02-17-18, 11:22 AM
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it looks like the paint crazed

Term is called checking! When dissimilar materials react to each other!
 
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Old 02-17-18, 11:39 AM
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Term is called checking!
Lest anyone think that "crazing" is an incorrect word to describe this phenomenon...
https://en.m.wikipedia.org/wiki/Crazing

Someone buy marq a thesaurus. ;-)
 
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Old 02-17-18, 05:11 PM
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Crazing is a result of excessive stresses, which may or may not be set up in the film during drying, and then are suddenly released
Crazing is a physical issue, not a chemical issue as the OP has described!

Thanks but having owned a auto shop for a few years I kind of know the correct terminology!
 
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Old 02-17-18, 08:46 PM
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Originally Posted by marksr
It should be fine. It may have been better to have waited a little longer before applying the finish coat but it's not a big deal. No need to start over! IF you were concerned about looks you'd just need to sand lightly and apply another coat of finish.
Definitely not concerned with looks. Only corrosion protection.
Additional coats over the fresh paint seemed to slide right off the cracks shortly after being applied. I was worried about the cracks causing the paint to peel and considered scrubbing it all off so I could do it right, but I asked here and decided not to. Instead, after it cured I sprayed it again from 8 directions (so 3-4 coats in a given area) at proper distance. I'll call it a success as paint didn't slide off the cracks. (Any white specks are just reflections. It is jet black.)


Also, whatever the term, it shouldn't have been caused from a chemical incompatibility as I only used primer because the can of black paint that I had had called for that specific product line. I thought it was a physical issue from applying too thickly. Unless some residual oil or sodium carbonate wasn't fully removed after the mineral spirits, alcohol, and compressed air (in a can) and leached through the primer... Well, thanks for the help.
 
 

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