Why using primier?

Bodner007,

I've had good luck using Testors spray enamel (light grey) as a primer for Testors Model Master acrylics. The key is letting the primer coat dry for a good long time (I waited a week) before applying the acrylics. I may have waited too long, but I wanted to be sure there was no problem.

From what I understand, acrylics over enamels is fine, but one shouldn't do things the other way as the enamel is somewhat "hot" and will eat into the acrylic paint.

Regards,

-Drew

I primarily use acrylics for airbrushing. Does it matter if I use an enamel or acrylic as my primer coat or is one better than the other?

Bottled or canned paint do not have to say "primer" on them to be used as such. Any flat paint can be used as a primer; just make sure that the "primer" you use is compatible with your topcoat. Lighter colors (grays and whites) can be used for lighter or dark color topcoats, while darker grays, etc. should only be used with dark topcoats. I typically use Testor's flat black and gray enamels as my primer coats, and have periodically used Floquil Reefer White with good success.
Gip Winecoff

I use cans that say 'primer' from the local automotive shop. Having said that, for metal figures, I used to use Humbrol's enamel flat white (with a touch of thinner to make it more fluid)...

Does it have to say "primer" on the can inorder for it to be primer, or can i use any paint (mixed differently or something)?
Also, i see that there are different primers in the stores... A metal one and a plastic one, and in different colors (white and gray, i think). Does it matter which i use? thanks.

Priming can serve a couple purposes:
1. It gives your topcoat tooth, like dj mentioned above.
2. It allows you to see any mistakes that need to be corrected prior to shooting your topcoat.
3. For me, an armor builder, I "prime" my models flat black, and then spray on a light topcoat so that the prime coat peeks through subtly; the primer acts as the very first step in the weathering process.
4. Lastly, depending on the color of the primer and the color of your topcoat, priming has the potential of either increasing or decreasing the intensity of your topcoats.

Gip Winecoff

I modelled many years without using any primer at all, so I'm fairly confident that you can still do it without too many problems. I only started using primer once I branched out into metal figures (for my dioramas) and realised that without a primer coat, the paint was fragile and did not resist long to any touching/handling...

Nowadays, most of my kits are 'upgraded' with metal, resin bits (wire, foil, photo-etched parts, accessories,..) and the primer give me an even surface to work on. Without it, I'd have paint sticking well to plastic, not so well to metal and possibly not at all on resin bits...

Also, many years ago, I did not do any weathering, while nowadays I do, and this treatment can be harsh (drybrushing in particular) to the kit. Unprimed resin and metal would suffer more than plastic...

So, all in all, I'd advise you to prime your models.