Robert Webster wrote:The Zpoxy and shellac thing might be a tempest in a teapot. After all, once you seal with shellac, apply the epoxy, and then allow it to cure, you're going to sand it all back to the bare wood. At this point the epoxy should only be in the pores. You can then seal and finish with whatever you like (except, perhaps, for varnish).
I've gone through that routine and have gotten results that we're initially excellent for a French polished surface. Unfortunately, epoxy fills all eventually shrink back a bit after 6 months to a year so that pores are once again evident. Same goes for the wishful thinking of using enough shellac to fill the pores. Shellac dries down extremely slowly over rosewoods and will sink back with time.
Not everyone sands back to bare wood, though - some people like the amber colored coat and leave a full Z-poxy layer, even using a 50/50 zpoxy/alcohol wash coat at the end to insure full coverage after level sanding. The warning may be more appropriate in these cases?
I've tested french polish shellac over a full Z-poxy coat on a test board, and it sticks fine and looks great, but I've never done this on a finished guitar - I usually sand back to wood.