Author Topic: Paints and chemistry  (Read 788 times)

Offline Errodynamic

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Paints and chemistry
« on: Sun Nov, 27, 2016, 10:06:PM »
Hey everyone.  Have to say I love this site...everyone is so supportive and informative.
Anyway..so I found some of my old model kits in my parents house, including the P-61 (with the white diorama picture on the box top)that everyone says is a real challenge. It has been sitting in the attic since probably 1982.  I painted it way back when but never started it.  I am sure it was a Testors rattle can but I don't think they had anything but enamels back then but not sure.  My question is, if I repaint it with an acrylic or lacquer, will they (the paints)react to each other and trash the model?  Also, can you switch between paint types or do you need to seal it first?  Don't think I am saying this very eloquently but I hope you get the point.  Very excited to get back in to the hobby and any help would be appreciated.
Thanks
Flynn

Offline urumomo

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Re: Paints and chemistry
« Reply #1 on: Sun Nov, 27, 2016, 10:12:PM »
  Nah  -  you're good .

  Once any of those coatings is cured it can be top-coated with the other .
With a word of caution with lacquers since their solvent content is so high  , they can soften acrylics  , but this usually isn't a problem with the amounts that are sprayed down .
 ..   adhesion may be a different story  ,   from paint to paint  --  but in a static model you only need it to stay put   ;)
 
« Last Edit: Sun Nov, 27, 2016, 10:13:PM by urumomo »

Offline Errodynamic

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Re: Paints and chemistry
« Reply #2 on: Mon Nov, 28, 2016, 08:25:AM »
Great,  thanks!

Offline Elm City Hobbies

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Re: Paints and chemistry
« Reply #3 on: Wed Nov, 30, 2016, 04:56:PM »
So long as whatever is on it is fully cured, and if they are as old as you say, then that wouldn't be an issue, you can put any type of paint over any other type of paint with no issues.

Quote
With a word of caution with lacquers since their solvent content is so high  , they can soften acrylics

Not necessarily true. I can put Testors rattle can lacquer paint over Vallejo acrylics without an issue. So long as the last paint laid down is fully cured, it isn't an issue.

It is more worrisome putting lacquers over enamels, as it takes so long for enamels to cure, while it may be dry to the touch, they can sometimes take a few days, weeks, even months to fully cure, depending on the paint. 

Offline urumomo

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Re: Paints and chemistry
« Reply #4 on: Wed Nov, 30, 2016, 05:29:PM »
   You chopped off the rest of the statement that qualified it for what you are saying .  ;)

   Spraying it down normally isn't an issue  ,   but if you let it pond or repeatedly soak the work  , the acrylic will solve .
     ... . try brushing lacquer onto acrylic  ...

    Once modified oil-based enamels cure  , they will be unaffected by lacquer solvents .
   Most every modern enamel will  be cured enough in 24 hrs  to tolerate any lacquer top-coat .

     EDIT   -  I'm talking about normal  applications of coatings  ,
                   Obviously follow the manufacturer's recommendations on cure time
     
« Last Edit: Wed Nov, 30, 2016, 05:51:PM by urumomo »

Offline Elm City Hobbies

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Re: Paints and chemistry
« Reply #5 on: Thu Dec, 01, 2016, 02:25:AM »
Try laying down Testors Lacquer over Testors enamel after only a day, and see what happens.

The problem with enamels is they take long to cure, and thus gas out, if you seal in the off gassing from the curing paint, anything you put over it while it is curing will usually crack, or some other odd item.


As far as acrylics, well they aren't all made the same either, but I can pool lacquer over cured Vallejo with no issues. Vallejo once cured is as hard as nails.

Try taking their primer out of an airbrush once it is dried into the airbrush, lacquer thinner won't even budge it, even soaking it in lacquer thinner for hours/days, and the paint won't budge. Once Vallejo is cured, about the only thing that will get it off is 99.9% rubbing alcohol, and even then it is a struggle.

Most other paints I can get to come off with Super Clean, brake fluid, Easy Off oven cleaner.....none of it will touch cured Vallejo. Even enamel and lacquer paints that have been on a kit for 20yrs are no match for something like Super Clean, but even it won't budge cured Vallejo paints.

Offline urumomo

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Re: Paints and chemistry
« Reply #6 on: Thu Dec, 01, 2016, 02:50:AM »

     ???

    I have absolutely no desire to argue with you Scott  ,
  I just want anyone tuning in here to be aware that Acetone , Toluene , MEK will solve acrylics .

    I use predominately Vallejo Model Color  .
        .. maybe I'm nuts  - so ,
  I just went and dug up scrap and palettes with tons of long , long cured Vallejo in all kinds of colors .
    Both the acetone and the lacquer thinner made short work of dissolving the paint .
     It always has in my world and that matches everything in all the books I have  -
      So ,
              I don't know what to say  .  The Vallejo here must be really different  ?
             I'm not trying to be a smart-ass  --  I honestly don't understand  what you are talking about .

      Acrylics cure through basically coalescing   --- the water thinner evaporates bringing the resin together and the glycol ether solvent evaporates and allows the resin to bind .       It's weak against strong solvents .
       Modified oils cure through oxidation  , sped up by catalysts  , and change chemically so they will no longer react .
       Lacquers are pure evaporative cure ,  and they are mostly solvent .
     

Offline Elm City Hobbies

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Re: Paints and chemistry
« Reply #7 on: Fri Dec, 02, 2016, 12:03:AM »
Well, don't know what to tell you, but I have successfully put lacquers over vallejo many times (granted their primer) and it doesn't take it off. Ditto with enamel paints over Vallejo primer.

Even trying to take the Vallejo primer off the kit, paint removers will take the paint off, but end up leaving the primer.

Vallejo paint dried in an airbrush as I forgot to clean it, soaked it in lacquer thinner, and didn't even touch it, tried other paint removers as well, nothing. Only thing that would take it off was 99.9% alcohol, and even then I had to really scrub it.....but it worked better than other stuff.