What is that yellowish primer?

[tom mann]

What is the rationale behind the yellow-ish primer that is seen on weathered tank cars and DRGW locomotives?  Why is it that color and not black?

[Bob Bufkin]

Tom

Depends on  what type of primer is used.  When I was in the navy, they orignally used red lead (done away with because of the lead), I believe there was a zinc primer which was a yellow color plus others.  It's been awhile but I would guess it depends on what chemicals, minerals, etc in the paint.

[Chris333]

Sounds like zinc chromate, it's made to etch into the metal.

[sparky]

Chris is right.  Most industrial finishes use a zinc-based etching primer as a first step.  The etching primer is usually two parts: The primer and an activator.  The activator contains phosphoric acid which etches the bare metal surface chemically bonding the zinc to the steel.  The zinc and acid will stop any surface corrosion that may have begun during manufacturing.  However, it will not prevent new corrosion.  The zinc primer is very porous and must be top coated to prevent moisture from reaching the surface metal.  Once the zinc primer is exposed, rust can begin to form.

[tom mann]

Here is a shot to show you what I mean:

http://www.rrpicturearchives.net/showPicture.aspx?id=339034

[Wlal13again]

Here is a shot to show you what I mean:

http://www.rrpicturearchives.net/showPicture.aspx?id=339034

Could that be heat discolor from the dynamic braking?

[TiVoPrince]

Here is a shot to show you what I mean:

http://www.rrpicturearchives.net/showPicture.aspx?id=339034

Could that be heat discolor from the dynamic braking?

Precisely!
SP units also exhibit this weathering pattern. With SP you also get lettering burned down to the red reflective layer as a bonus...

[Wlal13again]

Here is a shot to show you what I mean:

http://www.rrpicturearchives.net/showPicture.aspx?id=339034

Could that be heat discolor from the dynamic braking?

Precisely!
SP units also exhibit this weathering pattern. With SP you also get lettering burned down to the red reflective layer as a bonus...

Used to see that on the Espee units when I lived in El Paso...

[ljudice]

This may sound stupid - but isn't that just Orange paint - with the lettering/logo tape put over it and then everything sprayed black.  I agree it was burned off from the dynamic brakes.

I was always told the red on SP units was the base primer color - which was exposed when the scotchlite lettering burned off.

[Walkercolt]

Lou, the primer started life as light grey. I've gone into the BNSF yard, the UP yard, and the SKO yards in Tussa to scrape "paint chips" from cars and locomotives with my pocket knife. :-[ The heat from the dynamics burn thru the paint and the primer and you're seeing some light rusting. I've gotten "up-close and personal" with SP, Cotton Belt and one "Rye-O Gran" locomotives with this damage.(Hey, my buddy Rich is a BNSF conductor, and gets me in the yard. Wink-wink!) The SKO couldn't care less, but you have to watch out for the "street people" that hang out down there. : I thought the yellow on the tankcars was yellow zinc chromate primer(like the military uses), but according to the paint stencil on many badly weathered tankcars, it isn't. They mostly say "Glidden #XXXX latex primer applied 00-00-00", usually on the "B" end of the tank. Chip a bit of black or white paint off a sturrip, and the primer has some "give" to it, like not too old house paint. Strange. Fresh, it looks more tan than yellowish.

[Ed Kapuscinski]

We made an interesting discovery today. Apparently they used brown paint on the trucks of the SD80macs. It's not rust, it's actually brown paint.

I could swear I saw Tom sneaking off though right before we got to South Fork.

[Walkercolt]

Ed, I wonder if that's a powder coating(more heat restitant) on truck frames of locomotives. It seems very, very thick. On the Rockwell frames the "silver" on UP engines almost fills the Rockwell logo, and it doesn't seem to chip very much. Ain't it funny what you find out sometimes?

[ljudice]

remember the SP SD45T-2's (and some others) painted with the "environmentally friendly paint" that pealed off in sheets to expose a tan primer?

[Walkercolt]

Yeah and the first ATSF GP-60 "SuperFleets" the paint fell off in sheets from, because of the "enviro-friendly" water-based primer. NS had the same problem for a while. GM and Chrysler had major problems with that on their cars too, late 80's-early 90's. For a while, every white Lumina had a primer grey hood, roof and trunk. And the "K" cars paint peeled off like onion skin. The last of the "Warbonnet" BNSF's are looking really bad now. Peeling pink over rust and about Dark Lark grey hoods. Never dreamed I'd say it, but they'd look better in the "Swoose" now. :'(

[Wlal13again]

remember the SP SD45T-2's (and some others) painted with the "environmentally friendly paint" that pealed off in sheets to expose a tan primer?

Yeah, we called them the 'Desert Storm" units...