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Prepping Plastic Structures

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HM7
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Prepping Plastic Structures
Posted by HM7 on Sunday, January 5, 2020 1:46 PM

I understand that plastic strutures need a primer applied before painting.  I'll use an acrylic paint.  But what kind of primer?  Does the color matter - clear, white?  I'm building a Woodland Scenics model, but the instructions are not that specific.

 

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Posted by MisterBeasley on Monday, January 6, 2020 10:17 AM

It's important that the plastic surfaces be clean, but since structures don't get much handling, I have found that paint sticks well without primer.

Most of my plastic kits are of brick buildings, though, so my base coat is usually rattle can paint of brick color, and most often labelled as a primer, although that turns out to be the final coat.

You might find a light colored primer will allow you to get a more even coat with acrylic paint, particularly if the paint itself is light.

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

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Posted by mbinsewi on Monday, January 6, 2020 10:49 AM

I've never used a primer on any buiding kits or scratch builds,  the only exception is on rolling stock or locomotives, going from dark to a lighter color.

As Mr. B. said, making sure the surfaces are clean, is the important part, especially finger smuges from handling the parts.

By the way, Welcome to the forums!

Mike.

 

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Posted by jjdamnit on Monday, January 6, 2020 11:19 AM

Hello All,

HM7
I understand that plastic strutures (SIC) need a primer applied before painting.

I'm not sure where you got this information but there might be some confusion about using primer.

The traditional use of paint primer is to provide a sandable base for the final finish to be as smooth as possible, especially with glossy finishes on metal surfaces or when using body filler.

Primer fills in any surface irregularities, that's why primers are thicker than the paint(s) being applied.

For wood, the role of primer is to "hide" the grain, again to provide the smoothest surface possible.

Primers are designed to hide fine details. For some models this is undesirable.

When painting a brick structure, a primer might hide all the details of the brick.

You did not specify which Woodland Scenics kit you are building: brick, wood siding, stone block?

MisterBeasley
It's important that the plastic surfaces be clean...

Preparing the surface to be painted is probably more important than priming it.

If all the parts are plastic I use Dawn® dishwashing soap. I fill a clean sink with warm water add the soap and wash well.

Using gloved hands, rinse the parts thoroughly and allow to air dry.

After drying I handle the parts by their sprues or with gloved hands.

The oils from your skin can affect how the paint adheres.

I am currently kitbashing a Walther's Northern Light & Power structure.

The parts were washed as I mentioned above.

Because this is a brick structure I wanted to keep the mortar lines as deep as possible.

After splicing several walls together I painted them with Rust-Oleum "Gloss Merlot". This color best matches the desired finish I wanted. For a matt finish I could have use Rust-Oleum "Satin Cabernet".

After a 24-hour drying time I used Acrylic paint, in my airbrush, to paint the window sills and door frames a granite gray.

The reason I wanted the mortar lines as deep as possible is because, after all the walls were dry, I used a lightweight joint compound to highlight the joints.

If I was not going to use this final technique, I would have used the satin finish to avoid the sheen of the glossy paint.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by Doughless on Monday, January 6, 2020 11:21 AM

Flat sheen paint will stick just fine to a clean styrene surface.  Real buildings don't look glossy anyway, so flat is what you want.

The fewer the coats, the better the details show through, IMO.

- Douglas

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Posted by AntonioFP45 on Monday, January 6, 2020 11:24 AM

Hi,

Spot on info from the above gentlemen. Just wanted to add that it's worth the extra few minutes to thoroughly clean the surfaces of the parts that are to be painted.

Doesn't happen often but occasionally there may be traces of molde-release or some other waxy residue on some parts.

Wax & Grease remover, Windex, or 50% iso-alcohol, on a lint free cloth, work very well for most plastic structures. Washing thorougly and using gloves, as JJ above suggests is an excellent practice.

Unless a light color will be going over a dark color, I'll just spray my preferred color directly on to the structure whether via airbrush or rattlecan.

Suggestion:  Test practice on a scrap item first.  Goal should be to get the smoothest coats possible. This is why I collect plastic coffee / tea can lids and compact discs from my coworkers and friends, to use as test panels. It really helps!

 

"I like my Pullman Standards & Budds in Stainless Steel flavors, thank you!"

 


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Posted by UNCLEBUTCH on Monday, January 6, 2020 11:28 AM

I also, have never used a primer on any of my builds, wood or plastic. In fact I very seldom even clean them. I use craft paints.

I do apply a base coat sometimes, such as a gray, but thats for a weathered efect.

I even painted metal ,trucks and details without primer  no issues

HM7
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Posted by HM7 on Monday, January 6, 2020 2:22 PM
Thanks, gentlemen for your helpful replies. A good soapy, wash and one less step than I had thought.
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Posted by SeeYou190 on Monday, January 6, 2020 5:35 PM

I guess I will step up for the pro-primer modelers.

.

I prefer to prime my buildings a light gray because then it takes less paint to get an even finish.

.

Tamiya makes a fine spray can primer for applying to buildings with fine detail. It is an A+ product, but it is not cheap.

.

-Kevin

.

Living the dream.

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Posted by Boiler-man on Monday, January 6, 2020 5:48 PM

I have assembled several WS buildings and paint them with the craft paint that Wallyworld sells as it is cheap and covers well, no primer and I am using a paint brush. I would rather apply paint with my airbrush and use a sovent base paint however it is in srorage back in Nebraska.

Boilerman
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Posted by dknelson on Tuesday, January 7, 2020 10:10 AM

The late Art Curren (king of the kitbashers in his time) used to wash all kit parts in warm water and vigorously scrub them with an old toothbrush using Ajax or other lightly abrasive sink/bathtub powdered cleanser to both clean the plastic and remove the plastic sheen.  Of course Art's goal typically was to make use of the original molded in kit color and not paint at all and if you check out his articles in RMC and MR (the MR ones were collected in a soft cover book that is filled with excellent kitbashing advice) he had success with completely avoiding painting the kit walls while avoiding having them look like unpainted plastic.

Daringly, if he did paint walls he also wrote about and showed the results of brush painting plastic with thinned Floquil (solvent based) paint and again he had success where most of us would ruin the model.  He said the secret was just the right thickness of paint that only one coat was needed.  Well it worked for him ....

Another iconoclastic approach he took: he would utterly "over-cement" the joints between structure wall sides.  His goal was to soften the plastic so much that when he would squeeze the joint tightly, a combination of softened plastic and excess cement would ooze out of the joint.  He would let it harden then carefully slice it away with a knife.  Result: totally invisible joints between wall pieces.

Dave Nelson

 

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Posted by doctorwayne on Tuesday, January 7, 2020 11:39 AM

dknelson
...Another iconoclastic approach he took: he would utterly "over-cement" the joints between structure wall sides. His goal was to soften the plastic so much that when he would squeeze the joint tightly, a combination of softened plastic and excess cement would ooze out of the joint. He would let it harden then carefully slice it away with a knife. Result: totally invisible joints between wall pieces.

I always enjoyed his articles, and that tip with the glue is one that I use often, although I use solvent - originally lacquer thinner, but since they've changed its formula, MEK seems to be a fairly decent replacement. 
It's not all that great for doing large areas, though, as it evapourates much more quickly than did lacquer thinner.

Wayne

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Posted by wjstix on Thursday, January 9, 2020 3:00 PM

HM7

I understand that plastic strutures need a primer applied before painting.  I'll use an acrylic paint.  But what kind of primer?  Does the color matter - clear, white?  I'm building a Woodland Scenics model, but the instructions are not that specific.

 

I don't think there is such a thing as clear primer(?) In painting models made of plastic, a primer is used as a base to add the final color(s) over. It's not like say sanding sealer, it has nothing to do with filling in surface irregularities and doesn't obscure fine details - unless you're slathering it on with a trowel I guess. Primer paint - usually gray or white - is basically the same as regular model paint...it may have some difference but it's not much.

As Mr.B points out, a primer makes a big difference if you're trying to paint a light color over a dark model, like say painting a black plastic boxcar yellow or orange. You'll get a much better result if you put on a light layer of primer gray first.

I generally use Tamiya spray can primer gray. Unlike hardware store spray cans, than are often designed to cover large areas like when painting a chair or table, Tamiya spray cans create a fine spray pretty close to what you can get with an airbrush. It dries quite quickly; depending on the weather / humidity, it's usually dry within an hour or two.

Stix
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Posted by jjdamnit on Thursday, January 9, 2020 3:48 PM

Hello All,

wjstix
I don't think there is such a thing as clear primer(?)...

Yes, there is a clear primer for plastics.

Valspar brand "Primer For Plastic" (#68109).

When speaking specifically about paint primers, as I said before, these are intended to be a thicker coat to hide any irregularities in the surface to be painted.

These paint primers come in Gray and Red- -also labeled as "Red Oxide" and "Ruddy Brown". These primers are also known as "automotive" primers. 

Cody Grivno has recently been touting the use of Rust-Oleum® Painter's Touch® 2X, Ultra Cover Paint +Primer. A banner on the label touts, "Also Bonds To Plastic! (bold type used on lable).

I suspect the viscosity of these paints are somewhere between a traditional primer and the thinner topcoat paints.

If you are simply using another color to hide the original color these are known as "base coats". Any color can be used as a base coat.

Any paint, if applied too thick, can hide or mask the fine details of a model.

The OP was asking...

HM7
But what kind of primer?

In the vernacular of painting "primer" has a specific meaning.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by GNMT76 on Thursday, January 9, 2020 4:24 PM

Stix and JJ,

Thanks for the additional details.  That's good to know about Tamiya's fine spray! 

Kerry

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Posted by MisterBeasley on Thursday, January 9, 2020 4:25 PM

I usually do all my priming, painting and brick mortar work before any assembly, because it's easier to work on individual flat walls than assembled structures.  I glue a piece of strip balsa wood into the corners during assembly, to prevent any light leakage out the corner joint and give me a much larger gluing surface.  This is also when I glue horizontal supports on to the walls for adding interior floors and to support the roof.

Usually, I print patterns for floors and walls on the computer and install those, too, and I figure out how to light the individual rooms.  No wonder it takes me a month to complete a basic 4-walls-and-a-roof kit.

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

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Posted by ctyclsscs on Thursday, January 9, 2020 4:40 PM

jjdamnit
Vlaspar brand "Primer For Plastic" (#68109).

But that raises the question - does it actually help the paint adhere better?

The last time I built a display model I scrubbed the parts well and was still disappointed in how the Testor's paint came up where I masked some edges. I don't remember paint coming off that easily in the past unless they've changed the formulas.

Jim

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Posted by Doughless on Thursday, January 9, 2020 5:44 PM

Autozone and similar places sell clear primer for things like plastic bumpers that are made from shiny flexible plastic like what we have on modern model handrails and other detail parts.  I use this primer before painting these kinds of parts.

I would think that it would be excellent for structures also, although I don't know straight off that just because a primer may be safe for engineered plastics, that it would also be safe for styrene.

- Douglas

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Posted by garya on Friday, January 10, 2020 10:39 AM

doctorwayne

 

 
dknelson
...Another iconoclastic approach he took: he would utterly "over-cement" the joints between structure wall sides. His goal was to soften the plastic so much that when he would squeeze the joint tightly, a combination of softened plastic and excess cement would ooze out of the joint. He would let it harden then carefully slice it away with a knife. Result: totally invisible joints between wall pieces.

 

I always enjoyed his articles, and that tip with the glue is one that I use often, although I use solvent - originally lacquer thinner, but since they've changed its formula, MEK seems to be a fairly decent replacement. 
It's not all that great for doing large areas, though, as it evapourates much more quickly than did lacquer thinner.

Wayne

 

I've found MEK evaporates too quickly at times.  I've tried Xylene, which doesn't stick as quickly but doesn't evaporate as fast, with promising results.

Gary

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