Hi Chris;

There are only 3 types of finishes in the entire world at the moment: Enamels, lacquers, and 2-part finishes. UV cured polymers are probably considered a class of the 2-part.

If you apply a 1-part finish and it can be re-dissolved in its solvent, it is a lacquer. Nail polish is like this, if you drip lacquer thinner on a painted nail, the lacquer runs right off. Same is true of an original older 'Vette.

If you apply a 1-part finish and it does NOT re-dissolve in its solvent, it is considered an enamel. i.e., latex wall paint uses water as its solvent, but once it is dry (a chemical reaction with some constituent of air, usually CO2) causes it to change its molecular makeup. You can thin varnish with mineral spirits, but once hardened, you can't dissolve varnish with mineral spirits.

2 part coatings like epoxy have NO solvents, they are 100% solids. Nothing evaporates, the major chemical reaction is not with air, it is between the two substances mixed where the chemical reaction takes place. That is why they will cure underwater, for example.

Well, if varnish cannot be re-dissolved in its own solvent, and you apply a coat on top of a cured, sandable existing coat of varnish, that bond is purely mechanical. QED. On the other hand, lacquer will always soften the coat below and form a chemical bond, forcing the 2 coats into one. What does this prove?

Well, if people admit that #400 sanding between coats of varnish are acceptable, then a similar mechanical bond between i.e. epoxy and varnish should work just fine with an (i.e.) #400 sanding - And they do. The reasoning that #120 is necessary for "bite" between varnish and epoxy, but #400 sanding between coats of varnish is Ok is flawed, as it is the same problem in both cases. _Nothing_ special happens when you put varnish over what USED to be varnish. Mechanical bond plain & simple.

Sorry to be wordy, but let's stop the wive's tales.

Best Regards, Spidey