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Craft paints, plastic and glue

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  • Member since
    August 2006
  • From: Nashville, TN area
  • 634 posts
Craft paints, plastic and glue
Posted by hardcoalcase on Thursday, September 22, 2022 9:00 AM

I'm building the Heljan roundhouse and used Testors Liquid Cement to assemble the unpainted foundation sections.  I then painted the foundation and wall sections using craft paints to achieve the particular colors I wanted.  The craft paint adheres to the plastic well enough, but can be lifted off with masking tape.  

This has me thinking... will the craft paint prevent the Liquid Cement from proper bonding/welding of the plastic parts?  Should a different glue be used?  Is it better to just scrape the paint off the joining surfaces?

Jim

  • Member since
    February 2001
  • From: Wyoming, where men are men, and sheep are nervous!
  • 3,181 posts
Posted by Pruitt on Thursday, September 22, 2022 9:13 AM

hardcoalcase
...will the craft paint prevent the Liquid Cement from proper bonding/welding of the plastic parts?  Should a different glue be used?  Is it better to just scrape the paint off the joining surfaces?

Jim

Anything between the pastic at the mating surfaces will prevent proper bonding. You need to scrape the paint off the joining surfaces to get a solid connection. Here's what happened to me when I didn't do that:

In my case it was Rustoleum paint and Plastruct Bondene. According to Ask MRVP, Bondene would bond plastic joints right through paint. Not so much - in this case the "expert" didn't know what he was talking about. Here's how some of those joints looked after my roundhouse fell apart:

The Bondene crazed the paint on the window frames, but did NOT bond through it. 

Craft Paint and Rustoleum are not the same type of paint at all, but they are both contaminants between the plastic surfaces.

Do yourself a favor - remove the paint from the bonding surfaces before gluing.

  • Member since
    March 2011
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Posted by NVSRR on Thursday, September 22, 2022 9:26 AM

You can decrease the paint peal by just priming everything first.    remove the paint from mating surfaces.    What could help is assembling all the part that will be the same color in sub assemblies and then paint the subassemblies.      Then finish assembling.  Less touch up and not as much mating surface to clean and touch up.   

shane

A pessimist sees a dark tunnel

An optimist sees the light at the end of the tunnel

A realist sees a frieght train

An engineer sees three idiots standing on the tracks stairing blankly in space

  • Member since
    August 2006
  • From: Nashville, TN area
  • 634 posts
Posted by hardcoalcase on Thursday, September 22, 2022 9:29 AM

Pruitt
  You need to scrape the paint off the joining surfaces to get a solid connection. Here's what happened to me when I didn't do that: 

That's the best model of tornado damage to a roundhouse I've ever seen!Big SmileCrying

Thank you for sharing your hard-earned wisdom!

Jim

  • Member since
    November 2013
  • 2,309 posts
Posted by snjroy on Thursday, September 22, 2022 9:51 AM

I would say that letting the cement cure for 24 hours should be enough. As for the paint, craft paints are not the best when it comes to sticking to plastic without a primer. When I use masking tape, I always stick the tape on a bare piece of wood before applying on a painted model. 

Simon

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 20,582 posts
Posted by MisterBeasley on Thursday, September 22, 2022 1:32 PM

I keep blue painters tape around for kitbuilding.  I find it's easier to paint surfaces before assembly.  So, I carefully mask all mating surfaces first.

If I'm building something like a Walthers structure kit with thin walls that don't give much mating surfaces, I usually re-enforce the inside corners with balsa wood pieces glued in with CA cement.  This also helps with light leaks.

It takes an iron man to play with a toy iron horse. 

  • Member since
    July 2006
  • From: west coast
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Posted by rrebell on Sunday, September 25, 2022 8:54 AM

Craft paints on plastic are asking for problems. They work great on real wood though. Think plastic on plastic bond with no glue, just the static atraction of the two.

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