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  #1  
Old 03-04-2011, 02:47 AM
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dbrent dbrent is offline
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Default I hate rattle cans!

I managed to stuff up another simple paint job on my K-25 Alpha... Nothing complicated... just painting the black stripe and fin for the 1970s paint scheme. I had painted the entire rocket white, and let it dry for a week. Then I masked off the desired area with premium (green) masking tape, burnished all the edges very carfully, and shot 2 coats of the gloss black.

When I went to remove the masking tape, the paint along the edges lifted and came with the tape leaving a ratty looking ragged line. My guess is since I was painting over a gloss surface that the black didn't get a good enough hold.

I have to admit, spray can painting baffles me. When I do a plastic models, I typically shoot Tamiya flat acrylics through a double action airbrush and never have any trouble even with the most complicated paint schemes. I don't even consider that my paint might attack the primer, or that removing masking material will ruin the paint edge.

Don

Last edited by dbrent : 03-04-2011 at 03:08 AM.
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Old 03-04-2011, 08:30 AM
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Quote:
Originally Posted by dbrent
When I went to remove the masking tape, the paint along the edges lifted and came with the tape leaving a ratty looking ragged line. My guess is since I was painting over a gloss surface that the black didn't get a good enough hold.
That may be a factor. I usually, but not always, mask, sand, re-mask, then paint. Although sometimes I just paint over the cured, gloss finish without sanding.

It sounds like, in your case, you let the paint dry before you removed the mask. I learned, working in a paint shop, to remove the mask while the paint is wet, so that's what I always do.

Sometimes, it takes four hands, some painting jigs, cleverness and holding your tongue just right to get the tape off without marring the wet paint, but I don't get any flaking that way.

Doug

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  #3  
Old 03-04-2011, 09:02 AM
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Quote:
Originally Posted by Doug Sams
It sounds like, in your case, you let the paint dry before you removed the mask. I learned, working in a paint shop, to remove the mask while the paint is wet, so that's what I always do.
Doug
.


I agree here.
I seem to get a better mask line if I remove the tape before the paint has had fully dried.
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Old 03-04-2011, 09:05 AM
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Quote:
Originally Posted by Doug Sams
snip...cleverness and holding your tongue just right to get the tape off without marring the wet paint,...

^^^I've found this to be true.

But to the original problem; shooting it two times may have contributed as well. If you do that, you are for sure going to get a "lip" on the edge of the masking—even in a best case scenario. You'd have to sand, at least the edges, of the masked paint to get a clean release and then clear coat it. Tamiya paints (I think) don't have near the viscosity of typical spray can enamel.

I'm still screwing up rattle can jobs myself. The small Testor's cans of spray paint seem be be a bit thinner and have a better spray for smaller jobs, but then, of course, the little cans cost as much or sometimes more than a standard can of Rustoleum.
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Old 03-04-2011, 09:55 AM
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Quote:
Originally Posted by dbrent
I managed to stuff up another simple paint job on my K-25 Alpha..
Just curious, what brand & type of paint did this occur with? I've had this happen with rustoleum enamel, probably due to the what others have suggested here, but not with lacquers. (still living off my dwindling stock of old Krylon...)
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Old 03-04-2011, 11:13 AM
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Quote:
Originally Posted by foamy
But to the original problem; shooting it two times may have contributed as well.
That brings up good point.

Don, How long between coats of black did you wait?

FWIW, when I apply two coats of any color, they're just a few minutes apart.
...
My experiece in painting has been that the first coat functions as a "tack" coat. I just put on a thin application, with poor coverage, then wait 10-15 minutes. After that, I can put down a heavier second coat with little fear of runs. I then wait another 10-15 minutes, and apply a 3rd coat, if necessary, if there are still some thin or dry-looking spots.

Doug

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Old 03-04-2011, 11:17 AM
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Quote:
Originally Posted by Doug Sams
It sounds like, in your case, you let the paint dry before you removed the mask. I learned, working in a paint shop, to remove the mask while the paint is wet, so that's what I always do.

I did attempt to remove the mask while the paint was wet. I say attempt because I had most of the rocket masked off with blue painter's tape and it took awhile to get down to the green tape that was my actual masking line. I think the paint cured somewhat during the 5-10 min it took to get the tape off. I suppose I could reverse the order of my masking such that the mask line comes off first.


Quote:
Originally Posted by foamy
But to the original problem; shooting it two times may have contributed as well.

I know I said two coats but really it was one since they were only about a minute apart.

Quote:
Originally Posted by PaulK
Just curious, what brand & type of paint did this occur with? I've had this happen with rustoleum enamel...

Actually it is Rustoleum. I've been using their Ultra-Coat 2X. It's been working quite well for me but this is the first time I've tried to mask anything.
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Old 03-04-2011, 11:24 AM
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Quote:
Originally Posted by dbrent
... I had most of the rocket masked off with blue painter's tape and it took awhile to get down to the green tape that was my actual masking line. (snip)
I suppose I could reverse the order of my masking such that the mask line comes off first.
What I do here is lay down the line tape (usually the vinyl kind that doesn't wick under). This is the tape that forms the paint line. Then I apply the bulk mask alongside that, but leaving a gap. Then I apply masking tape over the gap.

That way, after spraying, all I need to remove is the tape over the gap, then the tape along the paint line. I can then leave the bulk mask in place over night if necessary since it's not in contact with the wet line.

Doug

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  #9  
Old 03-04-2011, 05:41 PM
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Quote:
Originally Posted by dbrent
...

When I went to remove the masking tape, the paint along the edges lifted and came with the tape leaving a ratty looking ragged line. My guess is since I was painting over a gloss surface that the black didn't get a good enough hold.

I have to admit, spray can painting baffles me. When I do a plastic models, I typically shoot Tamiya flat acrylics through a double action airbrush and never have any trouble even with the most complicated paint schemes. I don't even consider that my paint might attack the primer, or that removing masking material will ruin the paint edge.

Don


Hi Don;

I've never used the green masking tape, but the problem sure sounds like the solvent in the paint is too hot for the adhesive on the underside/edge of the tape. If the solvent dissolves the adhesive along the edge then no matter how much burnishing is done, the paint is still going to leak/wick under the edge.

An analogous problem could occur with the old formula Krylon paint. I typically like to use Tamiya masking tape, one of its properties being its thinness, which contributes towards some nice clean paint separation lines. But I found that if I laid the Old Krylon on too heavy, its hotter solvent would actually scald the surface of the underlying paint from above (the Tamiya tape being thin, and not being an adequate barrier in this case), leaving a rough patch when the making tape was pulled up. In this case, the problem wasn't the edge but the ability of the tape to be an effective barrier to the hotter solvent.

In your case, my money would be on trying a different masking tape with the paint you're using, and see what happens.
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  #10  
Old 03-04-2011, 05:46 PM
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Quote:
Originally Posted by foamy
^^^... Tamiya paints (I think) don't have near the viscosity of typical spray can enamel.

...


Well I think the point here is that Tamiya paints are acrylic based, and so are going to be fairly inert with respect to their interaction with tape adhesive.

As mentioned, I don't think it's a viscosity issue, I'm thinking its a solvent/tape adhesive interaction issue.

Just my best guess;
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