Furniture, Wood and Cabinetry Finishing - Furniture Refinishing

I have a number of cabinets that have a shellac finish over a poplar or alder-type wood. The areas exposed to moisture have alligatoring and cracking evident. I would like to refinish these to match the original cabinets that are still in good shape as closely as possible, but make them more moisture resistant by using a polyurethane finish over the shellac. I tried it on one piece and it looked and appeared to dry OK, but when I looked at my old can of clear shellac it had a note stating, "not to use shellac under a urethane." My questions are, Is it OK to place polyurethane over the shellac finishes I want to repair? Will I end up with a future problem like a sticky finish? Is there a better product to use?

Ron:

Shellac used to be a 'no-no' under any urethane finish, but times have chnaged. I'd check the urethane can to see if it's allowed or not. Some do, some don't.

An alternative to polyurethane, which should go over shellac with little problem is Minwax Polycrylic. The additional bonus of being a clear, non-yellowing finish would make it my choice.

One caveat, however. ALWAYS sand before applying a new finish - it gives the new finish something to hang on physically, since it will not bond with the previous finish chemically.

BTW - the alligatoring can sometimes be brushed out using a good natural bristle brush just dampened with lacquer thinner...