Spray paint problem: blistering

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greg33

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I teach a model rocketry class and am hoping to get the opinion of some of you on an issue we've been having.

We use the same type of acrylic spray paint but sometimes a coat placed atop another (black atop red in this case) doesn't adhere probably and bubbles up, blistering and giving the appearance seen in these linked photos:

I've run some tests in previous years and found that lightly sanding between coats usually helps, but in this case the problem still happened. We are using flat black paint since originally we thought maybe the glossy was the problem.

Any thoughts? In this case it was not the drying time that was an issue since the coat dried overnight before the next coat.

Thanks for any comments.
Greg

Hi res photos available here:
https://picasaweb.google.com/greg33...authkey=Gv1sRgCLOJrZfvlpqhiQE&feat=directlink

rocket paint.png

rocket paint 2.png
 
I'm guessing it was dry time. Most paints are pretty particular about recoat times.
 
Precisely!
The picture shows a classic lift crinkling so often seen when we don't adhear to the recoat times clearly listed on the cans. That was one of the best selling points for Old formula Krylon paint. it could be recoated at anytime. Look hard for other types of paint that carry this "recoat anytime" feature on the lables.

Because the underlaying coating has not yet fully cured the application of another coat softens the surface pulling in the under coat and primer.
You'll find when you sand this mess you'll have to go all the way to bare body tube again before the problem will go away.
 
Have to agree with the others, the paint is not dried properly before recoat. Let it dry, sand it down, repaint following the can instructions. I find rustoleum to nice glossy paint but the worst offender as you must follow the recoat times and then some to be safe. I have had great success lately with the new Valspar line at Lowe's the says recoat any time.
 
Great, thanks to everyone for the replies. According to the student he let it dry overnight which is what peaked my curiosity, but it seems unanimous here that this was not the case. Thanks again.
 
Actually, he may have left it to dry overnight, but some paints need as much as 72 hours to completely cure.

It pays to read the labels completely.

G.D.
 
Whoever you know that has "the nose" ..... you know who I mean..... if they can smell the paint, it is not ready for the next coat. Depending on humidity, temp, etc. some can take a week to dry properly. :fly:
 
It is super important to read the recoat time on the lable of every brand and type paint and primer used.

It's possible to use mis-matched products IF and ONLY IF the recoat times are followed to the letter.
Many Cheapy auto primers and many brands of rattlecan spray paint have recoat times listed something like

"Recoat within 4hours or wait 7 days".

many will have much shorter beginning recoat times as low a 1hour while others may only require 5 days beyond the initial coating.

The "Nose Test" Zog139 mentioned is helpful also. That is:

With your nose against the surface of the painted model if you can still smell it, it is NOT ready for the next coat."
What we are smelling is the paint thinners solvents and vehicle outgasing.
Hope this helps.
 
I moved the thread to the appropriate section
 
I'm not sure I buy the drying time theory. I admit you do have to pay attention to the dry time, but I think there are other factors. Why - because I 've had blistering on the first coat. I use enamel and acrylic (not together!) and have seen blistering with both in the past 4 or 5 years. I think the paint manufacturers have made changes in the formulas and the paints have become much more sensitive to whats below them and temp and humidity conditions. I live in FL and have learned not to paint in the summer. Rustoleum advertises 50% humidity and I get blistered paint jobs most every time I use it. Valspar is even worse. Testors seems to do much better, but only comes in small cans. I'm done using major brands of gloss acrylic on decal paper. They all blister. Tree House sold at HobbyLobby has been the best performer, but once again humidity is critical. I'm still searching for a solution for large rockets. I have an air brush for smaller projects and that has never let me down!
 
Whoever you know that has "the nose" ..... you know who I mean..... if they can smell the paint, it is not ready for the next coat. Depending on humidity, temp, etc. some can take a week to dry properly. :fly:
If I went by this rule I would be waiting months for some second coats. I just now went back to an almost finished rocket I haven’t touched in two or three months and I could still smell the paint.
 
I know its more than most spray paints, but I use only Duplicolor and never had any issues painting over other paints of the same brand. I also use their primers. I figure the extra money I spend is worth the time I spend re doing a paint job and all that sanding. No thanks. Sometimes I wait up to a week to paint the second color say red over white or whatever it may be? I'm usually not in a real hurry when I paint. $6-7 for a can of paint is a cheap investment.
 
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