What causes "snake skin" pattern in the spray paint?

[crg0813]

I sanded then painted the fins for my next project, thin coats, but when the last coat dried, it cracked like lizard skin. I used a good quality flat black spray paint. They are all sanded down now, but I don't want the same result again.
Thanks for any help
B

 

[smstachwick]

Maybe shrinkage in the paint or incompatibility with an undercoat?

Photos would be needed for a better diagnosis of the problem.

 

[neil_w]

What specific paint did you use, how many coats, and what was the exact timing of the coats?

 

[Scott_650]

Typically, but not always, that cracking paint snafu happens when the carrier solvent in the top coat/clear coat paint layers reactivates the paint in the base coat layer. Other factors can cause it but 90+% that’s what does it. Following the paint recoat times on the can and/or letting the base coat layer dry and cure completely (which, depending on conditions can take days if not longer) will help keep that from happening. But not always, today’s consumer grade spray paint has rather aggressive carrier solvents - having a solvent that “off gasses” quickly helps meet environmental standards for VOCs - so even if you do everything right: clean, oil/dirt free surface prep, use compatible paints, following recoat times, let the paint cure until it passes the “sniff” test (if you smell paint it ain’t cured) and laying on even, thin coats you can still get wrinkled or cracked paint. There’s only two absolute certain ways to prevent it from happening, never paint your rockets () or use water-based acrylics through an airbrush.

For me, the convenience of using commercial rattle cans is worth needing to occasionally sand it down and start over. For some folks switching to an airbrush and using lacquer or enamel or acrylic paints works (I have an airbrush but haven’t experimented with it yet). I’m generally happy with a decent 5 foot paint job so spray cans are ok, plus I have a boat load in the shop to use up. And plenty of sandpaper on hand.

 

[crg0813]

What specific paint did you use, how many coats, and what was the exact timing of the coats?

I used Rustoleum "Painters Touch Ultra cover primer" application time 4-5 hours between coats, with a light 600 grit sanding in between

 

[neil_w]

I used Rustoleum "Painters Touch Ultra cover primer" application time 4-5 hours between coats, with a light 600 grit sanding in between

There's your problem. Recoat time for that paint, as specified on the can, is within one hour or after 48 hours.

Within one hour means you apply your complete set of coats within a single hour, start to finish, then let the rocket sit for at least 48 hours (for that paint, I usually leave at least 4-7 days).

Typically, I leave 5-10 minutes between coats, that works well.

 

[crg0813]

Thanks, I will try again in a couple days, after another light sanding. I'm on disability so I have nothing but time
I can work on other things

 

[neil_w]

Thanks, I will try again in a couple days, after another light sanding. I'm on disability so I have nothing but time
I can work on other things

Painting is a never-ending adventure. Good luck!

 

[bcook7135]

Rustoleum paint is really bad about this. I have had this happen a few times. So what works for me especially on warm and humid times (I have to paint outside) is let the rocket and can of paint get acclimated to the temp outside and then paint. And the 1 hour - 48 hour is the rule. After 1 hour you need to let it sit.

 

[Lord Rory Gin]

Thanks, I will try again in a couple days, after another light sanding. I'm on disability so I have nothing but time
I can work on other things

Something else you can do is prep your spray cans by placing them in a pail of warm water for several minutes and then thoroughly shake them up (shake 2x as long as recommended) before spraying. Also unclog the nozzle completely. This will allow the spray to be more atomized into smaller droplets and hopefully a more even coat. JMHO, but that might help in allowing the carrier solvent to evaporate quicker.

 

[Ronz Rocketz]

For me, the wrinkles occur when I try to paint in the morning (before noon) when the humidity is up to 80%. My main problem is when the Rustoleum starts spattering. I believe this occurs when the contents precipitate no matter how much shaking occurs. I've been able to fix it by placing the can in bowl of hot water but don't do this for every can. One of these days, I'll finally clean out the garage and use the air spray gun I bought.

 

[neil_w]

For me, the wrinkles occur when I try to paint in the morning (before noon) when the humidity is up to 80%. My main problem is when the Rustoleum starts spattering. I believe this occurs when the contents precipitate no matter how much shaking occurs. I've been able to fix it by placing the can in bowl of hot water but don't do this for every can. One of these days, I'll finally clean out the garage and use the air spray gun I bought.

Rustoleum recommends painting only under 65% humidity, for what it's worth. I don't know if that would contribute to wrinkling, though.

 

[Ronz Rocketz]

Rustoleum recommends painting only under 65% humidity, for what it's worth. I don't know if that would contribute to wrinkling, though.

Believe me, yes.

 

[boomtube-mk2]

Are the fins/nosecone you're painting plastic?
Some of the plastic parts coming out of China these days have a tendency to still be outgassing from their molding.
It might even still have mold-release compounds stuck to them.

If they were not plastic, then the answers above would be relevant.

 

[crg0813]

Thanks guys...I bought a really cheap can at Walmart and it filled the bill