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Tamiya paint cracking; cause?


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To go a bit further, modelers came up with the rules that enamels are safe over lacquer (but not reverse), lacquer is safe over lacquer, and water-based acrylics are safe over everything.  But in real life, that often doesn't work.  There are just too many variables in play.  Things like what solvents are used, what type of resin is used as paint's binder, and similar things.  Even if someone compiled a huge list of what brands/types of paints are compatible with what, not only that list would be quite large, manufacturers sometimes change chemical formulas for their paints, so the list would not be accurate. Plus as you mentioned drying time can also affect the paint's behavior.

In your case, are you sure that the bottom coat is really a lacquer (the description on the label can be inaccurate)?  Or it could be that the solvent in the top coat is hotter (or chemically incompatible) with the bottom (lacquer) coat, causing it to expand and wrinkle. 

Like I mentioned, thank goodness for spoon testing.

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6 hours ago, peteski said:

In your case, are you sure that the bottom coat is really a lacquer (the description on the label can be inaccurate)?  Or it could be that the solvent in the top coat is hotter (or chemically incompatible) with the bottom (lacquer) coat, causing it to expand and wrinkle. 

Like I mentioned, thank goodness for spoon testing.

The Testors diamond dust is supposed to be a lacquer, yes. And I agree, experimenting on my kits themselves is an absolute no-no. The thing is, the other spoon, (different primer though), turned out just great, and even allowed for an additional coat of Tamiya clear red lacquer over the clear orange, which I very much like.

D 10.JPG

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1 hour ago, Roadrunner said:

The Testors diamond dust is supposed to be a lacquer, yes. And I agree, experimenting on my kits themselves is an absolute no-no. The thing is, the other spoon, (different primer though), turned out just great, and even allowed for an additional coat of Tamiya clear red lacquer over the clear orange, which I very much like.

D 10.JPG

WOW! That is PRETTY!

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8 hours ago, Roadrunner said:

The Testors diamond dust is supposed to be a lacquer, yes. And I agree, experimenting on my kits themselves is an absolute no-no. The thing is, the other spoon, (different primer though), turned out just great, and even allowed for an additional coat of Tamiya clear red lacquer over the clear orange, which I very much like.

Well Kevin, you have answered your own question. You just proved how unpredictable mixing various brands of paint (including primer) can be.  As you noted, in this case the brand of primer seems to make difference.  Maybe the solvent from Tamiya paint penetrated the Testors paint and affected the primer.  I don't have a specific answer as to the reason for the wrinkled paint, but I know mixing paints often causes problems (as you are proving here), and testing the paint combinations on a spoon is the best course of action. Well, except that the kit's plastic itself can also be the part of the safe painting equation.  Safest option (that I usually go with) is to minimize the number of coats on the model. Whenever I can, I use model (plastic compatible) paints and no primer.  But we all have different painting techniques, and some are riskier than others.

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16 hours ago, Roadrunner said:

The Testors diamond dust is supposed to be a lacquer, yes. And I agree, experimenting on my kits themselves is an absolute no-no. The thing is, the other spoon, (different primer though), turned out just great, and even allowed for an additional coat of Tamiya clear red lacquer over the clear orange, which I very much like.

D 10.JPG

So what two primers did you use? Seems the one that did work is the primer you should use with this combo you’re doing. 

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8 minutes ago, Dpate said:

So what two primers did you use? Seems the one that did work is the primer you should use with this combo you’re doing. 

Seems reasonable...but the exact formulation of the styrene whatever material is going over can have an effect too.

Spoons are not necessarily the same "styrene" as model kits. Nor are all the kits even from one manufacturer the same, especially these days.

Testing on an inconspicuous area of whatever you want to paint, particularly if you're trying to mix different brands of materials, is pretty much mandatory.

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3 hours ago, Dpate said:

So what two primers did you use? Seems the one that did work is the primer you should use with this combo you’re doing. 

Dupli-Color black lacquer & Tamiya white lacquer. The one with the black primer is the one that cracked all to heck.

Edited by Roadrunner
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1 hour ago, Roadrunner said:

Dupli-Color black lacquer & Tamiya white lacquer. The one with the black primer is the one that cracked all to heck.

Ah okay.  Never used Dupli colors primers - even though lot of folks have had success with it using automotive paints n such. I strictly use Mr surfacer primer. If I wasnt packing for my move I would test myself as I have few cans of the testors  extreme diamond dust. Something in the 3n1 testors didn’t agree with the dupli color or vice versa. 

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5 hours ago, Roadrunner said:

A few hours, if I recall correctly.

Anything questionable, make up a sample first in case it breaks bad. I use the overnight rule, most of the time, between primer and paint. It gives me the option to sand the primer a bit if it needs it.

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First off I would wait at least a day minimum or two might be better. If you have a dehydrator I would use it to speed up the process.

When you mix paint brands you are always run the risk of compatibility issues.

You really are better off to stick with one brand for the paint process. If there are windows for recoating the manufacturer will tell you. When you mix brands you lose that advantage.

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14 minutes ago, Dave G. said:

IDK, but it just seems to me one doesn't have to wait very long at this forum or look around very hard for that matter and someone is having trouble with either Duplicolor or Rustoleum spray paints on their models. To me there is a message there !

I never have problems with Duplicolor...other than crazing of bottom-of-the-barrel late-model kit "cost-engineered" "styrene".

I wonder why that is.

Rustoleum, however, is for lawn furniture and bird houses...though their "Rusty Metal Primer" works well protecting steel things that have to be temporarily stored outside.

Edited by Ace-Garageguy
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1 hour ago, Ace-Garageguy said:

I never have problems with Duplicolor...

I take it back. Ackchooally...I did have a problem when I shot Duplicolor universal black color over long-cured Ace Hardware store-brand black 'lacquer".

Cracking, because the hardware store paint wasn't sufficiently solvent resistant even after YEARS of drying.

Duplicolor primers are formulated to be used under real-car paint, and I've used them successfully under real-car lacquers, acrylic enamels, and acrylic urethanes including basecoat/clearcoat products.

That's not to say they're guaranteed to always work as model primers, or that the formulas won't be changed at some time, rendering them as useless as Plastikote (which used to be one of the go-to primers for experienced modelers) is now.

So test, test, and test if you have any doubts about product compatibility.

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Duplicolor lacquer primer and paint is good stuff, but because the solvents are "hot" for styrene it has to be treated carefully when used on plastic models. Lacquers cure by chemically bonding to the coats underneath. If the primer coat is on the thin side, a heavy second coat can have the solvents get trapped and cause the underlying styrene to soften and react.

You have to let the solvents gas out really well whether you are shooting multiple coats of primer or color coat over primer so those solvents don't activate the coats underneath and have those solvents penetrate the primer (barrier) coat and react with the styrene. If you dust on multiple coats of primer and allow plenty of time for the solvents to evaporate, the primer will better act as a barrier to prevent color coats from getting all of the way through.

While Testors and Tamiya lacquers carry much "cooler" solvents better suited to styrene, if they are shot on too heavy too quickly, they can activate an automotive  primer that isn't quite finished gassing out to hold those hotter Duplicolor solvents under subsequent coats against the styrene rather than allowing them to completely gas out. 

While I usually use an automotive lacquer primer when I am going to use an automotive lacquer color coat, for Testors and Tamiya paints I would use a Tamiya or Gunze primer (and still allow ample time for underlying coats to fully cure). There are many users who have successfully used Tamiya and Gunze hobby primers under automotive lacquer color coats too, but I would err on the side of caution when doing so i.e. very thin coats with ample time to flash.

I have many failed paint experiments under my belt, and in my experience Duplicolor primer really does need lots of time to cure to properly protect a styrene model kit body. I suspect it was the Duplicolor solvents remaining in the primer layer that caused the reaction OP has gotten rather than any of the Testors or Tamiya solvents shot over top.

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2 hours ago, gman said:

... Lacquers cure by chemically bonding to the coats underneath. 

No.

Lacquers "cure" by evaporation of the solvents in them.

Everything else you wrote is fine, but the above isn't.

Lacquer solvents do indeed penetrate into some plastic substrates, some more than others, they definitely penetrate into any previous coats of material, and subsequent coats of material can indeed retard the evaporation of solvents in underlying coats...which can result in a surface that squirms around or expands unpredictably when topcoats are applied, leading to cracking or wrinkling that looks like the effect of lacquer shot over enamel.

But as Duplicolor primers are, in general, much more solvent-resistant than any hobby primers, properly applied and aged Duplicolor primers should be fine under any hobby paint.

Still, TESTING of any material combination you want to use ON PLASTIC THAT'S THE SAME AS THE MODEL YOU'RE TRYING TO PAINT, and applied and aged exactly the same way, is imperative to avoid problems like the OP had.

 

 

 

Edited by Ace-Garageguy
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15 minutes ago, Ace-Garageguy said:

No.

Lacquers "cure" by evaporation of the solvents in them.

 

 

 

I'm picking the nits here, but lacquer never cures. Dry, yes, and can be rock-hard, but it's never cured. A little soaking or scrubbing with lacquer thinner or acetone and it can be rubbed right off. 

I know you know it, but I've seen the "lacquer cure" thing a few times here in this thread and thought I'd throw in $.02 worth...

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4 hours ago, restoman said:

I'm picking the nits here, but lacquer never cures. Dry, yes, and can be rock-hard, but it's never cured. A little soaking or scrubbing with lacquer thinner or acetone and it can be rubbed right off. 

I know you know it, but I've seen the "lacquer cure" thing a few times here in this thread and thought I'd throw in $.02 worth...

Agreed, and that's why I put the "cure" in quotes.

Lacquers remain sensitive to lacquer solvents, will "re-wet" even after years because they dry by simple solvent evaporation,...and some react like enamels that harden on the surface, but never dry through....leading to the cracking like I experienced shooting Duplicolor color over hardware-store lacquer after many years.

The only refinish materials that "cure" through are those that are catalyzed, and harden by chemical cross-linking of their constituent molecules.

 

Edited by Ace-Garageguy
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Unfortunately, even catalyzed materials sometimes remain "solvent sensitive" depending on several factors. I've had "fully cured" catalyzed acrylic urethanes, when topcoated with basecoat/clearcoat during repairs (catalyzed urethane clear) explode in wrinkles, just exactly like old synthetic enamel topcoated with lacquer would do.

This is most often a problem when some cowboy painter who doesn't bother to read instructions or stay within one company's compatible product line shoots his catalyzed topcoats over an enamel or "non sanding" primer. He might get away with it, but pity the poor SOB who comes along behind him during a repair...even years later.

 

Edited by Ace-Garageguy
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