Poly over shellac?

[deepsplinter]

I'm hanging some trim for a friend. To get the color we want, I stained it then put some amber shellac on it. You guys told me to put something over the shellac (poly) since it's going in a bathroom. I don't usually do this, but I read the fine print on the can of shellac. It days, "Not recommended for use as a sealer coat under polyurethane".

I attended a two day finishing seminar by Bob Flexner. He said (numerous times) that manufacturers instructions aren't always right.

What's your experience with poly over shellac?
What's the worst that could happen?

[sawduster]

The amber shellac likely is not dewaxed (and if it is the Zinnser stuff in the can it has a passle of other ingredients as well to extend its shelf life). One of the things you hear in finishing circles is to not put another finish on top of shellac which has not been dewaxed as the wax will hinder adhesion. What you can do is to add a coat of Zinnser Sealcoat over the amber shellac. Sealcoat is available in big box stores and is a dewaxed 2 lb cut shellac. You can then apply poly over that without issues.

[deepsplinter]

Wax huh? Well that makes sense.

Not what I was wanting to hear, but thanks all the same, Jerry.

I guess I'm off to find some Zinsser Sealcoat to put over my Zinsser shellac. (what a racket)

[Joe Lyddon]

You can ALSO just remove the TOP portion of the container which is dewaxed.

The wax settles to the bottom...

So, do not mix it up, and, as they say "decant" the clear stuff OFF into another container to get dewaxed stuff...

Waxed shellac should only be used for the Final top coat(s).
(if that's what you want)

If you want to put lacquer or poly over the shellac, it should be dewaxed shellac or it will not adhere to poly, etc.

[sawduster]

The 3# Zinnser stuff in the cans contains a crapload of other stuff to make it last longer on the shelf. You won't get but just a very small amount of stuff to decant off of the top and I don't think that is actually pure shellac and alcohol.