To prime or not to prime???

[gpharo]

I am currently in the process of painting an undecorated loco, a Proto 2000 SD60m. I am using the Tamiya TS spray paints for plastics.  I know priming the loco won't hurt, but is it necessary to prime the undecorated loco?

Thank you in advance.

[jrbernier]

If the shell is grey - you should be OK. Many times there are add-on detail parts that are black. With certain colors, you do not get even coverage. A good grey primer helps here. My MILW GP9'S are P2K units and are molded in grey. After adding various detail parts, I have grey/black/white locomotives! I spray whatever grey is handy over the entire model, then spray the orange color. I get a nice even coat of orange...

Jim

[ricktrains4824]

Solid undecorated grey unit, with no work done to it, you could get away with just paint. Any modifications, any added on parts, any changes made from stock, prime. (And, if black undec, prime for lighter colors.) 

Now, me, I use a base coat of primer every time. (I usually add something additional to undec units.) And, with certain colors, any color change from the original grey will show. (And you DO NOT want this showing through on the final paint scheme.)

[G Paine]

It also depemds on the color of the final coat(s). With dark colors, you may be able to get away with no prime coat. White, off-white, yellows, oranges and some reds or greens do not cover that well and need a light gray prime coat to hide dark color plastic or detail parts that are a different color from the base material.