. . . So you are saying 2 stage (or 2 step) does not mean there is a first step, then a second step?
. . .
A two stage paint of course means there are two elements, typically a catalyst or an activator (no they are not the same), depending on formulation and base resin system.
. . . I always thought a tri-stage (3 stage or 3 step) meant a base, a mid coat and a top coat.
So you are saying a tri-stage requires 2 extra 'elements' before it's ready to shoot.
And a 4 stage requires 3 extra elements before spraying. What are the 3 extra "elements" you are referring to? . . .
You are making it more difficult than necessary. Simply put, a single stage paint is one that doesn't need anything done to it, before application. Now, this does mean a single stage paint might need to be cut, to get through a gun, but generally a viscosity reduction (unless it's a reactive viscosity modifier for example) doesn't count in the "stages". I currently have a friend working with some pretty sophisticated 6 part paint systems, in the aerospace industry (NASA). The type, formulation and details of these elements isn't especially important and quite technical.
. . .Single stage clear? Never heard of that either . . .
Yep, run down to your local Ace Hardware store and pickup a can of Ace brand clear urethane. It's a clear poly acrylic urethane (they have a solvent base too) and indeed is a single stage clear top coat. In fact, most of the WR-LPU's (water borne) can be used without it's activator, though it's not as hard or glossy when cured and also has less gloss retention, but it still cures and acts much like the 2 stage product it's derived from.
. . . Also, you are stating that you can take a single stage paint (which in your definition would mean it does not require any hardener), and directly coat it with a 4 stage paint (which in your definition is a paint that requires three extra elements before spraying). Why would you want to do that?
what is your definition of 2K primer? . . .
Naturally, compatibility issue can crop up, but in many cases you can over coat a single stage paint with a multi and vise-a-verse. I wouldn't try this unless you have a firm grasp of the chemistry involved.
A two pack primer is just as it sounds and a two component product, that have to be combined, before application, excluding a cut for viscosity control.
To conclude, the typical base/clear coat systems are 2k's (each). If the base has limited environmental protection, you could consider the base/clear coat as a symbiotic package, so it's technically a 4 pack. Technically, it's still a 2 pack, as the clear can stand on it's own, in regard to UV and other environmental protection, though the base may be dependent.
