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Cure time between coats?

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  • Member since
    June, 2017
  • From: Pottsboro,Tx
Cure time between coats?
Posted by Mars on Wednesday, December 13, 2017 1:24 PM

Testors , Humbrol and most spray paints say to wait 48 hours before repainting. On something with 3 or 4 colors this can turn into over a week to get something painted, if I can stay on schedule. Is there more to the curing process than the evaporation of the thinner? I put painted items in a small heated bathroom for a few hours and they seems ready .

  • Member since
    October, 2010
Posted by hypertex on Thursday, December 14, 2017 7:30 AM

Mars

Is there more to the curing process than the evaporation of the thinner?

If we are talking about oil-based paint, then yes, there is more to the curing process. The hardening process involves oxidation, which triggers cross-linking of the polymers. The cross-linking process is very slow, but the result is a stronger, more solvent-resistant film. If you re-coat too soon, you risk dissolving the undercoat with the fresh topcoat. Such is the down-side of enamels.

In general, adding heat will speed up a chemical reaction. So your idea of putting a model in a heated room is sound. I know that many figure painters who paint with oils will build a drying box to put their figures in. It's basically a wooden box heated by a light-bulb. I have also heard of some modelers using a food dehydrator I have even heard of a modeler who put his models in a gas oven, heated only by the pilot light.

I have no idea of this actually works, but in theory it makes sense. But who knows how much time it takes off of the curing process? Your best bet is to experiment on some scrap models that you don't care about.

  • Member since
    November, 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Thursday, December 14, 2017 9:32 AM

I use Testors enamels, which are notorious for their long drying time.  I built an inexpensive drying box, and it speeded up the time by at least a factor of four.  It runs at 105 degrees so it does not melt nor warp plastic.  I use a 60 watt incandescent light bulb for the heat source.

I have several friends that use the dehydrators. It is important to get the right one- some run so hot they do melt or warp plastic.

Don Stauffer in Minnesota

  • Member since
    November, 2008
  • From: Central Florida
Posted by plasticjunkie on Thursday, December 14, 2017 2:20 PM

I have been working on multiple color schemes like German WWII aircraft ones and freehand have done at least two to three colors in one day using enamels or acrylics waiting about an hour between coats . If I have to mask with masking tape then I wait at least one day to make certain the tape does not pull up the paint. I have shot MM enamels and an hour later, masked with silly putty for  a soft edge and have not pulled the paint up. Granted that silly putty is more gentle that using masking tape but would never mask with tape so soon.

Now, If I'm going to shoot lacquer or enamel over acrylics then I wait a couple of days or more (oh no that's a no no!!) well I still do it and have NEVER had an issue over cured acrylic. I shoot clear flat lacquer over cured Future (acrylic) all the time as others here also do.

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  • Member since
    December, 2002
  • From: Bury St Edmunds, Suffolk, England
Posted by Bish on Thursday, December 14, 2017 3:33 PM

I mainly use enamels and like PJ, if doing free hand schemes i can do several coats in one day, but for msking i generally wait 48 hours. But then as i mostly build diorama's, thats when i get to work on figures adn other bits, so i am never in a rush.

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  • Member since
    September, 2006
  • From: Bethlehem PA
Posted by the Baron on Friday, December 15, 2017 4:14 PM

Don Stauffer

I use Testors enamels, which are notorious for their long drying time.  I built an inexpensive drying box, and it speeded up the time by at least a factor of four.  It runs at 105 degrees so it does not melt nor warp plastic.  I use a 60 watt incandescent light bulb for the heat source.

I have several friends that use the dehydrators. It is important to get the right one- some run so hot they do melt or warp plastic.

 
A drying box and a dehydrator are popular methods among figure painters, too, especially those working with oils.  Another method some use is to put a figure in those little crock pots that were popular back in the 90s for potpourri.  As you mention, temperature is key.  A gentle warmth is best.

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  • Member since
    September, 2012
Posted by GMorrison on Friday, December 15, 2017 4:52 PM

Air flow is as important, so if you can set up a fan too, so much the better.

Remember, enamels dry from the inside out, remaining tacky until nearly cured. Acrylics dry from the outside in, getting a non tacky skin almost immediately but taking a while to dry internally.

Thin coats dry way faster. I've pushed times to as short as eight hours using thin coats. If I'm in a hurry I can paint over coffee, paint over dessert and finish coat the next morning. Better than a couple of thick coats applied every 24 hours.

But if possible, a couple of days is always ideal. 

  • Member since
    November, 2017
Posted by jmb667 on Friday, February 16, 2018 5:30 PM
Dredging up this old thread, as I've been fighting with this myself. For MM enamels, I've found that good air flow and 24 hours seems to work well (especially when trying to mask camouflage).
  • Member since
    July, 2004
  • From: Sunny So. Cal... The OC
Posted by stikpusher on Friday, February 16, 2018 7:19 PM

Two months old is not bad. Now threads that are five plus years old can make you scratch your head as to why...

As far as painting with MM or Humbrol enamels goes, like the others here, I’ll do soft edge multi color free hand scheme colors one after the other with only the time required to clean the airbrush jar of the old color and prepare the new color in between. But if any masking is involved I’ll allow the color being masked to dry at least overnite before I apply any sort of masking. Planning ahead and working light to dark colorwise helps.

 

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  • Member since
    January, 2014
Posted by Silver on Friday, March 02, 2018 11:48 AM

Acrylics are the best.Oil base never fully dry and always bleed into each other.

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