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Craft paints, plastic and glue

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  • Member since
    May 2008
  • 14 posts
Posted by roundhouseman on Saturday, October 15, 2022 7:52 PM

I sometimes build models of dirt track race cars, from the 1960's-70's era. I do more painting of these cars than I do of railroad models at the moment. Though I have built several plastic RR kit buildings in the past couple of years. I am switching to mostly acrylic paints now, which most craft paints are. I have a cheap airbrush and if acrylic paint is thinned properly it sprays well and adheres well. The air brush gives me much greater control and you can put another coat on in only 5 mins as acrylic dries rapidly. You can apply as many coats as you need to get the desired coverage. No waiting hours for paint to dry. I spray plastic surfaces with mostly Rustoleum gray or white primer. I use black primer when I want to put silver or some such over it to darken the color. Craft paint is dirt cheap. Acrylic paints in Hobby Lobby and other craft stores are also dirt cheap. I find I can mix any color I want from them and not have to buy tons of different colors of paint. It thins with water. Can't beat the price. When I mix a color I mix enough so that I have some left in case I have to match it again some day. The vast majority of model car builders I am familiar with use acrylics and an airbrush. The primer leaves a sliightly rough surface to which acrylic paint adheres nicely to. I spray only flat colors which most craft paint often is. Or it certainly flattens when you thin it for the air brush. If you want some version of gloss or satin you can put your choice of clear coats on after. I often use CA to stick painted surfaces together but you are merely gluing the paint. If you want a solid styrene bond you need to glue the surfaces clean, nothing on them or the styrene bond does not happen. I have found that craft paints used this way, work well and are great for my paint budget.

RM

  • Member since
    July 2006
  • From: west coast
  • 7,215 posts
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.

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 20,710 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
    November 2013
  • 2,358 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
    August 2006
  • From: Nashville, TN area
  • 640 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
    March 2011
  • 1,543 posts
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
    February 2001
  • From: Wyoming, where men are men, and sheep are nervous!
  • 3,219 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
    August 2006
  • From: Nashville, TN area
  • 640 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

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