Poly will not be a sufficient barrier for leaking plumbing either.

But, you can sand and apply poly over the shellac. Just use water based poly----much less odor---as oil based will cause a long term smell problem.

Yes, almost anything sticks to shellac. As far as protecting against leaks goes... have you considered polyester resin? :)

For small, short-term sources of moisture, a couple coats of poly are certainly better than nothing (or shellac).

Thank you for your responses. No--never thought of the resin--I'll have to look into that one--how about lingering odor with the resin?

I was kidding about the resin. It's generally used for boatbuilding: expensive and waaayyyyy overkill. Poly is a fine choice.

Just kidding!!! LOL

But, I did use a Minwax water-resistant Polyurethane--I can't think of the name or term--I'm not posting on here from my home---baby sitting the grand-kiddies that are napping right now!

I used a palm sander and really went to town on that single coat of shellac and then used this poly-treatment. We had a minor leak from a newly installed water filter system---it dripped over-night to make a nice 18" by 10" puddle by morning and the surface worked great! Now I'm thinking to silicon caulk all around the bottom seams of the cabinet to really make it safe for any future minor leaks!

Thanks for the help!

When I think of it and am home--I'll post the name of that finish! Oh, it seems to me that it was Helmsman-Spar-Urethane (?), or something to that effect! No---I'm not thinking Mayonnaise either! LOL
Janice