The fundamental choice is epoxy resin base or polyester resin base. Given a suitably prepared surface (freshly sanded and cleaned), either will stick to aluminum. The epoxy out-sticks the polyester. Either is flexible enough, if not applied too thick.
The solids added to the resin base can be microballoons (glass or phenolic, i.e white or reddish brown), talc, ground plastic, wood flour, and/or a whole bunch of other stuff. Pre-mixed products generally claim some special recipe (such is commerce), but consulting the MSDS will offer a clue as to what is really in them.
Microballoons and talc are the most common. Micro (hollow spheres) adds bulk with little weight. Talc is heavier for a given volume, but sands smoother.
I tell you all this because a builder can easily mix whatever he likes.