shellac as grain filler?

[McCreed]

Simon has given you good advice as well some pros & cons.

I'll just add that shellac is typically not as durable as lacquers and poly's and tends to be fairly brittle for a guitar finish. Especially if applied too thick it will likely check over time. If it was a great guitar finish, all manufacturers would using it. It does have it's place(s) in guitar building though.

I have grain filled mahogany with shellac using the "slurry method" which is literally wet-sanding with shellac so that the wood dust mixes in with the shellac (like the talc Cliff mentioned) and creates a slurry, hence filling the pores.
However, my top coat there after has been either Tru Oil or an acrylic lacquer.

I'll also use shellac a sealer on a substrate that may have remnants of an unknown finish on it. My motto: If you don't know...SHELLAC IT! You can lay pretty much anything over shellac. That's one of the beauties of it.

As for using the shellac as a sanding sealer and then using alcohol based stain over it, I'm not sure how that would go.
IMO the stain is not going to penetrate the wood sufficiently and will likely just re-activate the previous coat of shellac. I could see that getting messy. I may be wrong, and can't say with certainty, as I've not done quite what you're describing.

[arie_shapira]

would a water based stain work over shellac?

[arie_shapira]

(it seems like an interesting material, so i wanted to see what i can do with it)

[McCreed]

would a water based stain work over shellac?

Stains and dyes work via absorption into the wood fibres, unlike paint which essentially adheres to it.

If there is any substance such as glues, oils, sanding sealer (shellac) etc, they will repel the stain and therefore not allow penetration into the wood fibres.

[Simon Barden]

A search of the web shows that you can stain over shellac, but you pretty much have to then apply more shellac over the top of it to seal the colour in. As McCreed says, the stain won't penetrate it, so will sit on top, and without protection, it will rub off. My gut feeling is that without spraying on the shellac over the stain, at least the first few coats, you're likely to rub off stain in patches if you rub on more shellac.

There are a whole list of things that are possible to do, but very few of them are the best way to do things.