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overpainting enamals with acrylics

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Is there a problem with painting over enamals with acrylics, or visa versa? I tried painting Polly Scale over Tamiya and the result was cracks that looked like spiderwebs. I know these are both acrylics, but I just wanted to make sure the experts say its ok before I try it.

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I think the key to any painting of any kind over another is to let the first coat completely dry.

 

The top layer will gas out and be dry to the touch in hours or a day, but it will still be curing. Also, when you use the SAME paint type your solvent in the overcoat has the potential to soften the bottom coat again. The heavier the paint coats, the more likely an interaction due to more solvent being present.

 

As for the cracking, that is usually caused by the bottom layer drying at a slower rate than your top coat. The top coat dries, THEN the bottom coat finishes drying (and shrinks a bit) cracking the top coat in the process. The variables here can be paint thickness, allowed drying time between coats, paint brand drying time (different lengths needed for different manufacturers), or all of the above.

 

What I said above is a simplification of how paint dries, but it does apply to most cracking problems. The real key is patience and controlled application. Hope this helps!

 

GIL :smiley16:

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I remember seeing the correct order to paint them in somewhere. For example, I don't think you can generally spray lacquers over acrylics, but you can spray acrylics over lacquers. (as Gil said, once everything is properly cured) I think the way it goes is, the 'hotter' the spray, the closer to the base, and you'd get cooler as you move away from the base.

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Acrylics over enamels should be fine. The easy way to remember what goes over what, is the relative strength of the solvents. Cooler or less aggressive solvents are generally OK over hotter solvent based paints. So the order would be(hotter to cooler) lacquer thinner or acetone, enamel thinner, alcohol, and then water base paints. If you put a more aggressive thinner over a less aggressive, the problem becomes that the hotter thinner dissolves the cooler paint and it expands and you get an alligator skin effect.

 

Cracking the the opposite problem. Cracking comes from different shrink rates. Although paints may be dry to the touch and hard enough to polish, they continue to shrink for much longer. If the top coat is shrinking faster than the lower coat, then you get cracks. So when you are mixing types of paint the longer you can wait between coats, the less likely you are of getting cracking. When spraying similar type of paint, you have two choices, either spray with little time in between coat or give it time to cure as completely as possible.

 

Now these are generalities and each paint you have will react differently depending upon the chemical makeup. Unfortunately although types of paint are generally the same, every manufacture has it's own mix, so composition is different and reactions are different. The only way you can be sure to get consistent results is to experiment and keep a log. The log should include, temperature, humidity, dilution rates(thinner to unmixed paint), and air brush pressures as a minimum. If you can describe your technique(distance from and speed across the target) these will give you an edge in getting a good paint job.

 

Good luck.

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I have airbrushed enamels over acrylics with no problems. First you have to let the acrylic paint dry for about a week to make sure it is dry alway through. When you airbrush the enamel paint you need to put it on very light in many coats until you get a good cover over the other paint.

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Is there a problem with painting over enamals with acrylics, or visa versa? I tried painting Polly Scale over Tamiya and the result was cracks that looked like spiderwebs. I know these are both acrylics, but I just wanted to make sure the experts say its ok before I try it.

 

From what I've read from the experts, everyone here has given you good advice, but may I suggest the more relevant term is cured rather than dry. There's a difference between dry to the touch and chemically cured, and what everyone here is driving at is the latter.

 

A good rule of thumb is if the paint on the model is still giving off an odor, it's not cured yet.

 

Regards,

Bruce

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A good rule of thumb is if the paint on the model is still giving off an odor, it's not cured yet.

 

Wouldn't that be a rule of nose? :lol:

 

Bruce is right--if you still smell a "paint smell", the paint hasn't thoroughly outgassed, and is therefore not fully cured. And that rule applies to all paints....

 

R

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But I love the smell of Dullcoat in the morning..... :smiley2:

 

GIL :smiley16:

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But I love the smell of Dullcoat in the morning..... :smiley2:

 

GIL :smiley16:

Or the smell of fresh Dullcote on the contest table!?!?!? Been there, done that. :smiley10:

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Cool! This way I can "sniff out" your models Ken! LOL! Can't wait!

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Cool! This way I can "sniff out" your models Ken! LOL! Can't wait!

Yeah....um......a......I have been known (aka notorious) for literally working all through the night in the hotel room (getting an occasional 15-20 minute nap) finishing a model, and walking into registration 15 minutes before closure with the finished model! I'm probably one of the guys whose models you've smelled gassing out at the Nats. Funny thing though, I've got about a 90% success rate of placing with those "All-nighters". Two of em nabbed 1st places, in loaded cats! It is my hope that this year I will not do the all-nighter. I'm working right now on getting those that are close, finished before driving out. See ya in Phoenix. :smiley4:

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