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Peeling paint--what am I doing wrong?

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  • Member since
    February 2003
  • From: USA
Peeling paint--what am I doing wrong?
Posted by senojrn on Saturday, September 27, 2008 8:43 AM

I have been working on a couple of aircraft models and have lately run into some serious problems.  Here's the setup:

Airbrush: Badger 250

Compressor setting: (a utility compressor with reservoir), pressure setting 30-40 psi

Paint: Model Master Acryl thinned to "the consistency of milk" with MM Acryl thinner.

Model Prep: washed with warm, soapy water prior to assembly (just OOB & while still on sprue).  After assembly and just prior to paint, wearing latex gloves, I wipe the model down with a lint-free cloth and rubbing alcohol--let dry for 30 min to 1 hr in front of a fan, then wipe down with a dry, lint-free cloth. 

On one model, I used a spray can primer (MM Enamel primer gray), let dry for 2+ weeks. 

I paint the model with the base color, then let dry for 2+ days.  Mask with the low-tack 3M painter's tape (purple stuff) and/or 3M Post-It notes.  Paint my second color, let dry for 15 minutes, then remove the masking. 

PROBLEM: On one model (Lindberg's 1/72 H-3), the paint (under the masking adhesive) peeled in only one 1" section--all the way down to the primer.  On the other model (DML 1/48 Me-163 Komet), under ALL the masking adhesive, the base color paint peeled off all the way down to the plastic.  Banged Head [banghead] Censored [censored]

What did I do wrong?  Any help, suggestions or advice would be greatly appreciated! 

NOTE: This technique has been succesful for me on 30 other model airplanes and only 1 other time, did I peel a 1/8" section of paint (but that was my mistake).

  • Member since
    January 2003
  • From: Peoples Socialist Democratic Republic of Illinois
Posted by Triarius on Saturday, September 27, 2008 10:40 AM

First of all, drop your airbrush pressure. For siphon fed, about 15 to 20 psi or less. For gravity fed, 10 to 15 psi or less.

Thin to the consistency of 2% milk—a little thinner than you probably have it. 

For washing, wash the parts (assembled or not) just before painting with Simple Green or a surfactant cleaner (Windex works too). Rinse first with tap water, then rinse with distilled or deionized water, followed by a wipe with either 90% isopropyl, ethyl, or denatured alcohol.

The reason to wash just before painting is that the plastic contains compounds called plasticizers that slowly migrate to the surface. Between the time you wash the parts on the sprues and the time you paint, more plasticizer may have migrated to the surface. Some plastics contain more of these compounds than others. Different manufacturer's plastics may perform differently, or even the same manufacturer's plastic may (does) vary over time.

Also, some manufacturers use more mold release than others. Depending on the composiiton of the styrene, the temperature, and the dwell time in the mold, there is a potential for the plastic to absorb mold release agent near the surface of the mold. This will also slowly migrate to the surface over time. 

You should wait a minimum of 24 hours between coats of acrylic paint, especially if you are masking over a coat. Acrylics dry quickly but cure slowly. They do not develop full bond to the substrate until they are fully cured. Do not mask until the underlying paint is fully cured.

Ross Martinek A little strangeness, now and then, is a good thing… Wink

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