Using automotive paint

[Ace-Garageguy]

45 minutes ago, Donny said:

New question, how do I save a post, it's a pain having to go back and try to find one with info you want to keep. Thanks. 

If there's a particular post with really valuable information I don't want to lose or have to hunt for, I'll copy it and save to a notebook somewhere on my own drive, labeled as to what it's about.

[stitchdup]

7 minutes ago, Donny said:

Does this show the "thread", or just that post?

just the post. if you want to save the whole thread this way just click the opening post. or you can always bookmark it on a computer

[Donny]

20 minutes ago, Ace-Garageguy said:

And another thing: lacquer made for cars, whether it's primer or colored paint, has hot solvents in it that are capable of pretty much ruining some plastic model car bodies.

It's never happened to some people, so they insist it's not a thing.

Yeah, well, it just hasn't happened to you YET.

Plastic car models, though they're all made of stuff in the polystyrene family, have exact chemical compositions that are all over the board.

Some are extremely solvent resistant (like some old Johan plastics that even liquid cement will barely touch).

Some are soft and will craze badly under the mildest of lacquers.

So do your research, and TEST before you commit to painting a model body with anything.

Here's a place to start:

 

 

For anyone getting into model car building or like me re-entering it, this is a dangerous and confusing subject. You really need to be a chemist to understand this stuff, me, I'll just take what I can onboard and go the trial-and-error route. I'll just have to take the chance on a few mistakes, like crazing and wear the consequences. Can crazing be repaired with sanding? I never experienced this way back when, maybe it didn't happen then with different materials.

Don 

[Donny]

24 minutes ago, stitchdup said:

just the post. if you want to save the whole thread this way just click the opening post. or you can always bookmark it on a computer

Thanks Les, normally just the post. 

[Ace-Garageguy]

26 minutes ago, Donny said:

...Can crazing be repaired with sanding? I never experienced this way back when, maybe it didn't happen then with different materials. 

Yes, no, maybe. It partially depends on how much surface detail there is, like wipers and emblems and handles, etc. Sanding to remove crazing will pretty much obliterate them.

On the other hand, if the body doesn't have much molded-on detail, sanding and re-primering can indeed save even a bad one.

This Gunze Ferrari 250 GTO hood crazed badly, as did the rest of the car...because I didn't TEST FIRST.

You can't really see it on the full body shot, but it's just as bad. It was a fairly expensive kit and I really didn't want to throw it out or buy another one.

I saved the hood and the rest of the body by lightly sanding it with 400 wet, then spraying a few coats of made-for-models high build primer, and sanding some more.

HOWEVER...most of the panel lines had to be re-scribed because they got so shallow during sanding.

Still, in the end, I was able to save it 100%, and she's almost ready for paint...which will be Tamiya lacquer this time, made for models.

Edited Thursday at 10:33 PM by Ace-Garageguy

[stavanzer]

Steve G. has it right.

Good Body Surface Prep. 

Good Primer Coats.

Good Paint Colour Coats.

The key is doing each step as well as you can.

And expecting that there will be duds, and recovering from them.

If you don't already have a Paint Stand, get one or make one. If you have some old model kits, you can use them for 'test mules' to practice painting techniques.

I'm sure others will chime in to expand or correct my thoughts.

Good Luck.

[gtx6970]

For me Key is , and especially rattle can paints made for 1/1 cars 

 

A - test first 

 

B - even then spray light coats.

 

I use Duplicolor rattle cans quite a bit. Usually sprayed straight from the can.  And they can be a bit hot and/or go on to thick if you're not careful.

 

 

Edited yesterday at 02:24 AM by gtx6970

[Donny]

Nice save Bill, you were saying about having to rescribe, I don't have a scribe tool, should I get one, or can I use a blade?

Don

[johnyrotten]

58 minutes ago, Donny said:

Nice save Bill, you were saying about having to rescribe, I don't have a scribe tool, should I get one, or can I use a blade?

Don

The back of an old #11 blade works well. Steady hand,light pressure to start. 

[Donny]

21 minutes ago, johnyrotten said:

The back of an old #11 blade works well. Steady hand,light pressure to start. 

Thanks mate, saves a bit of coin. 

Don

[Donny]

11 hours ago, stavanzer said:

Steve G. has it right.

Good Body Surface Prep. 

Good Primer Coats.

Good Paint Colour Coats.

The key is doing each step as well as you can.

And expecting that there will be duds, and recovering from them.

If you don't already have a Paint Stand, get one or make one. If you have some old model kits, you can use them for 'test mules' to practice painting techniques.

I'm sure others will chime in to expand or correct my thoughts.

Good Luck.

Alan, when you guys say the paint is a bit "hot", don't know what that means.

Don

[johnyrotten]

1 hour ago, Donny said:

Alan, when you guys say the paint is a bit "hot", don't know what that means.

Don

Aggressive, more potent solvents. Hotter solvents are more prone to damaging plastics. 

[Donny]

9 hours ago, johnyrotten said:

Aggressive, more potent solvents. Hotter solvents are more prone to damaging plastics. 

And as I'm not a chemist, I guess the only way to tell and be safe, is the spoon test. 

[stitchdup]

13 minutes ago, Donny said:

And as I'm not a chemist, I guess the only way to tell and be safe, is the spoon test. 

once you remove the parts from the sprue your left with the perfect test piece. the sprue is the same plastic you will be painting so why use spoons if you have left over sprue. 

[StevenGuthmiller]

28 minutes ago, stitchdup said:

once you remove the parts from the sprue your left with the perfect test piece. the sprue is the same plastic you will be painting so why use spoons if you have left over sprue. 

Not only that, but who’s to say that the plastic spoon is exactly the same composition as the model you’re painting.

I’ve heard the argument numerous times that plastic spoons are in fact a poor comparison to kit plastic for testing solvent affects.

They can be good for checking color, but I certainly wouldn’t rely on them to tell me whether or not a paint is safe for a particular model kit.

 

 

Steve

Edited 23 hours ago by StevenGuthmiller

[stitchdup]

1 minute ago, StevenGuthmiller said:

Not only that, but who’s to say that the plastic spoon is exactly the same composition as the model you’re painting.

I’ve heard the argument numerous times that plastic spoons are in fact a poor comparison to kit plastic for testing solvent affects.

They can be good for checking color, but I certainly wouldn’t rely on them to tell me whether or not a paint is safe for a particular model kit.

 

 

Steve

spoons are quite like the old monogram plastics, hard and brittle, while current kits are a fair bit softer. the kit plastic doesn't need to hold up to heat like the plastic silverware does unless you use the hood to stir yer coffee. also some of the knive handles make great kustom running boards for 30s cars

[Ace-Garageguy]

1 hour ago, Donny said:

And as I'm not a chemist, I guess the only way to tell and be safe, is the spoon test. 

The oft-touted "spoon test" is essentially useless for checking paint compatibility with kit plastics.

I've explained repeatedly that kit plastic compositions vary widely, and you have NO reason to expect some random plastic spoon will be the same formulation as the specific kit you're working on.

Yeah, they're all basically a version of "polystyrene". And that's as far as it goes.

For that matter, spoons from a reputable manufacturer made of styrene will most likely be MORE solvent resistant and harder than kit plastics, owing to them supposedly being "food grade". So your "spoon test" often tells you nothing.

AND...NOT ALL plastic spoons are even made from polystyrene. There are other similar looking but chemically different plastics out there.

The ONLY valid test you can make with spoons is color checking, and even that isn't guaranteed to be dead accurate, as paints CAN actually dry different colors when applied over different plastic substrates.

 

 

 

Edited 22 hours ago by Ace-Garageguy
accuracy

[StevenGuthmiller]

1 hour ago, Ace-Garageguy said:

The oft-touted "spoon test" is essentially useless for checking paint compatibility with kit plastics.

I've explained repeatedly that kit plastic compositions vary widely, and you have NO reason to expect some random plastic spoon will be the same formulation as the specific kit you're working on.

Yeah, they're all basically a version of "polystyrene". And that's as far as it goes.

For that matter, spoons from a reputable manufacturer made of styrene will most likely be MORE solvent resistant and harder than kit plastics, owing to them supposedly being "food grade". So your "spoon test" often tells you nothing.

AND...NOT ALL plastic spoons are even made from polystyrene. There are other similar looking but chemically different plastics out there.

The ONLY valid test you can make with spoons is color checking, and even that isn't guaranteed to be dead accurate, as paints CAN actually dry different colors when applied over different plastic substrates.

 

 

 

And there you are.

Couldn’t agree more.

 

 

 

Steve

[Donny]

2 hours ago, stitchdup said:

once you remove the parts from the sprue your left with the perfect test piece. the sprue is the same plastic you will be painting so why use spoons if you have left over sprue. 

I just thought that the sprue might not be a big enough area for a test 

[Rodent]

19 minutes ago, Donny said:

I just thought that the sprue might not be a big enough area for a test 

You can also use the outside of an interior tub, extra parts you aren't using, or the topside of the chassis to get a larger area. Anything that won't show on the finished kit.

[Bainford]

2 hours ago, Donny said:

I just thought that the sprue might not be a big enough area for a test 

It's not, really. As Steve says above, there are more effective areas for testing.  When doing your testing, apply the paint fairly heavy. If the plastic/paint combination is prone to crazing, give it the best chance to show that it will.