Best paint or primer for bright cast metal underframes?

[crossthedog]

Guys. You know those Roundhouse freight car kits with the cast metal underframes? They come with a lot of flash that you have to file off? Welp, when I last assembled some of these cars I gave the underframes a coat of some Testors flat black enamel before putting the cars together, but after I'd built them I noticed that my fingernails easily scratched the paint right off.

Seems suboptimal.

I have acquired a RH tank car kit with a very visible underframe, and I'd like to paint it before assembly. What to use? Just a little rattle can of Rustoleum primer? What do YOU use?

Thanks in advance,

-Matt

["JaBear"]

Gidday Matt, for what it’s worth, I use “CRC Red Oxide Primer”  rattle cans on bare metal. I suspect that the Rust-Oleum Automotive Primer, Red, rattle cans would be a similar product.

 

½  Cheers, the Bear.

[dstarr]

After filing off the flash, and doing any other file work, Dremel work, whatever work I do surface prep.  Wash in hot water and dish detergent, clean up with an old tooth brush, rinse well in hot water and then dry overnight.  Then I use Rustoleum or Krylon dark gray auto primer from a rattle can.  Sticks good and is a better color than just black. 

[SeeYou190]

All advice is good. We seem to have different preference for primers, which is personal and fine. You need to use a primer that matches your modeling techniques.

I prefer Rustoleum flat black automotive primer for metal underframes.

Your results might vary.

-Kevin

[Little Timmy]

I usually just spray on some flat black ( usually Testors, or Tamaya ) followed by a dullcoat .

However: Occasionally, I will spray on some Gloss Black, and then bake the frame in the oven at about 130 degrees for 45 minutes .

( My wife just recently bought me an autoclave to bake parts in ... seems my paint fumes in the oven didn't help the flavor of roast beef ...)

 

[EMDSD40]

I had success with air brushing Model Master flat black directly on the metal frame followed by a healthy coat of Dullcote clear flat. Of course all the flash filing done first. I've had no issues as the work was done 30 to 40 years ago. That has been my experience, good luck.

[ricktrains4824]

On unpainted metal parts, I usually use Krylon auto primer. It has a lot of tooth and grabs quite well.  

[crossthedog]

SeeYou190

I prefer Rustoleum flat black automotive primer for metal underframes.

Thanks for all the responses, guys. I mounted an expedition to excavate a corner of the garage where I thought I'd seen a can of Rustoleum primer. I found it and it was flat black. It worked really well. So far it "grabs" very nicely.

-Matt

 

[SeeYou190]

crossthedog

So far it "grabs" very nicely.

Most Rust-O-Leum products take two or three days to fully cure.

After that time, it will be even better.

-Kevin

[crossthedog]

Little Timmy

However: Occasionally, I will spray on some Gloss Black, and then bake the frame in the oven at about 130 degrees for 45 minutes . ( My wife just recently bought me an autoclave to bake parts in ... seems my paint fumes in the oven didn't help the flavor of roast beef ...)

This reminds me of a story my local hobby shop guy tells about some really old Chooch portals and abutments he came into. I forget what they're made of (resin or something?), but they were curved with age. He put them in the oven and baked them until they lay flat again, which worked like a charm, but he said he was in the doghouse for a month because that's how long the kitchen smelled like old burnt resin castings. 

 

[SeeYou190]

crossthedog

I forget what they're made of (resin or something?), but they were curved with age. He put them in the oven and baked them until they lay flat again, which worked like a charm, but he said he was in the doghouse for a month because that's how long the kitchen smelled like old burnt resin castings. 

This also works for flattening curved resin wall castings for Magnuson buildings.

Wait until your wife is out of town.

-Kevin

[Overmod]

Pickle the underframe in strong vinegar or muriatic acid or whatever, rinse it thoroughly, and use 'etching' primer.  Then any paint or weathering you use should adhere just fine...

crossthedog

...old burnt resin castings.

Get you one of those baking bags and put the pieces inside it, sealed up, sitting on a small sheet of baking parchment to preclude any reaction with the bag plastic...

The very best baked chicken is made by putting the meat, potatoes, onions, carrots and spices in the bag and letting 'er soak for a few hours at 275 to 350F.  It was my favorite... even better than London Broil or Lobster Newburg... in the early days of those bags.  Before the explosions started.  The new better-vented ones should still be good enough, though.  Just don't put the resin castings in with the food, or re-use a 'casting' bag for making dinner... 

[dknelson]

SeeYou190

 crossthedog

So far it "grabs" very nicely.

 Most Rust-O-Leum products take two or three days to fully cure.

After that time, it will be even better.

-Kevin

 

The usual advice is that if there is still a strong smell of the paint, leave it alone it is still drying/curing.

Ordinarily just about any rattle can paint should be fine on the white metal of a Roundhouse freight car kit, or similar metal underframe.  Until it finally ran out of paint and/or gas, for years I used a rattle can black paint meant for outdoor grills, a sort of matte finish paint with perhaps a light touch of gray in it.

 

But if you have been busily addressing the flash that those MDC/Roundhouse underframes have, you likely have deposited plenty of body oils from your hands onto the metal.  That probably accounts for the flaking paint problem reported by the OP

 

Since the (simplified) air brake details are cast-on the Roundhouse/Model Die Casting underframes are not easy to further detail but if you intend to add the piping from valve to reservoire and cylinder, I advise drilling those holes BEFORE painting.

 

And somewhat OT but if you ever see one at a swap meet, the old old (old) MDC all metal kits are kind of a hoot to build with the proviso that given their age now the boxcar sides and roofs might be brittle so don't force-fit things if you can help it.

 

Dave Nelson

[doctorwayne]

dknelson

But if you have been busily addressing the flash that those MDC/Roundhouse underframes have, you likely have deposited plenty of body oils from your hands onto the metal. That probably accounts for the flaking paint problem reported by the OP

Good point, Dave.

I also clean-up the excess flash, but on the car shown below, also modified the underframe to match a particular prototype. 
The frame (and the carbody) took a dish-detergent dip in the sink, then, after a thorough rinse, were left to air-dry...

The next day, I used small pieces of masking tape to properly position the turnbuckles and shield the portion of monofilament line that passed through them, then airbrushed the entire underbody using Floquil Grey Primer.

Here's the underbody in primer, with the masking tape still in place...

The next day, the underframe got a coat of Floquil (or perhaps Pollyscale) Black then the masking tape was removed and the turnbuckles were carefully brush-painted, leaving the monofilament within the turnbuckles clear.

I scratchbuilt new Hutchins ends, to match those on the real cars...

...then, with the underbody removed, airbrushed the car, then used C-D-S dry transfers to letter the car.

Currently, my go-to for primer is airbrush-ready Alclad II Lacquer Grey primer & Microfiller.

There's a fairly extensive thread HERE on building and modifying freight cars to match specific prototypes.  Lots of in-progress photos and some of my glitches and recoveries, too.

Wayne

 

[Medina1128]

Back in my drag racing days, we would paint with a product from a company called VHT (Very High Temp). Bake it in the oven, and it cures quite hard.

[crossthedog]

Overmod

It was my favorite... even better than London Broil or Lobster Newburg... in the early days of those bags. Before the explosions started.

!

dknelson

But if you have been busily addressing the flash that those MDC/Roundhouse underframes have, you likely have deposited plenty of body oils from your hands onto the metal. That probably accounts for the flaking paint problem reported by the OP

That could very well be. My fingers were all over the undercarriages that I painted black before. However, I also think that the Testors enamel was not as good a choice as the Rust-0-Leum primer.

doctorwayne

I scratchbuilt new Hutchins ends, to match those on the real cars...

Those grab bars are amazing, Wayne. I don't even see any glue strings

Medina1128

Back in my drag racing days, we would paint with a product from a company called VHT (Very High Temp). Bake it in the oven, and it cures quite hard.

Marlon, I'm trying to figure out how you fit a dragster in your oven.
-Matt