Yes ,Chuck you can apply it over Z-poxy or shellac.
We discussed this recently in this threadhttp://luthiersforum.com/forum/viewtopic.php?f=10101&t=20692.
It is easy to apply, but as it goes on very thinly can be a little unforgiving of poor preparation, so create a smooth surface for it with whatever grade of paper you are happy with.
To apply the tru-oil, I use ordinary kitchen paper, invert the bottle onto the paper and before using it on the wood make sure that the oil is absorbed into the paper rather than sitting on the surface, remember you are going to apply it in very, very thin coats. Rub with the grain of the wood in long straight lines, it's almost as if you are trying to rub it off rather than apply it. It will dry quickly so you can do three or so sessions a day. I like to build to about 12 coats. You can just rub back with a very light abrasive, I think Dave White uses OOOO wire wool, between sessions. When I have got to the level I want, I gently hand buff it with my fingers (have to rethink that one now I guess!
) this will slightly burnish the surface. I then leave a few days then rub it back with rottenstone in oil and if needed finish with Maguiars swirl remover.On tops or oily woods it is a good idea to apply it over spit coat of shellac.
Colin
like thats ever going to happen! lol