[rsxse240]

if your model is made of gray or white plastic, then primer isn't necessary for an out of the box build that has no body filler, no sanding work...and so on, AS LONG AS YOU ARE USING MODEL PAINTS!!!

now if you are building a car that the body is made of 2 different colors, then primer will be necessary.

also, if you are building a model that is made of (for example)red plastic. you will need to seal the plastic with some sort of primer, or use similar colored paint. red plastic, use red paint only. blue plastic can work with most grays, blues, blacks, dark greens. the reason for this is that the pigments in the plastic will "bleed" through the paint, causing discolorization.

also if you are using a semi transparent paint (or any light/bright colored paint) you NEED a primer so it doesn't look like dyed plastic when you are done.

I'm sure all of this is in the F.A.Q. section, but I need to practice typing! haha