dewaxed (hard) shellac on top of waxed shellac as sanding sealer?

[JurgenV]

Hi,
I think this is a newbie question but I don´t know and as this guitar is for a customer I don´t want to risk problems.

I hope someone here can tell me if I can use hard shellac on top af a waxed shellac with pumice as sanding sealer. Up to now I alway just used the hard shellac to fill the pores. I wanted to try the pumice version but just bought a ready made solution. ... And didn´t notice it said they used waxed shellac as base.
What could happen? Is it an absolute no-go?

[Mark McLean]

Generally speaking shellac is compatible with virtually any other finish including oils, nitro, poly and other varnishes. It can go under them or on top of them and not cause any problems. The only caveat is that some sprayed finishes (most notably nitro) may react poorly with underlying layers that contain silicone or wax, and the important adverse effect is "fish eye" defects where the nitro adheres poorly and is repelled by the wax/silicone. Therefore, if you are putting on a sealing coat of shellac and you intend to spray nitro as a top coat over it - you want to avoid using a shellac that contains wax. However, if your top coat is going to be more shellac, or an oil finish - or practically anything but nitro - you will probably be fine even if your shellac sealer was a waxed one. If in doubt, apply some more dewaxed shelac over your cured and hardened waxy shellac to seal over the initial seal, then go to your top coat of choice.