Zinser sealer shelac and clear shelac?

[Matt Edwards]

I'm in the process of finishing a gift for the missus. I already has several coats of zinser clear shellac on it, I thought I might top coat the top with poly for more durability, but I dont think the regular is de-waxed. I picked up a can of the zinser sanding sealer shellac that is dewaxed so I don't make the same mistake again. Question is, can the seal stuff be applied over the regular, then polyed over that?

Matt

[Ken Fitzgerald]

Matt,

It is my understanding that 100% dewaxed shellac can be put over anything and then anything can be put over it.

[Matt Edwards]

Cool! Thanks Ken, I'm kinda getting down to the wire on this one and didnt want to make a big mistake this late in the game.

Matt

[Scott Holmes]

NOT TRUE...

Shellac that still has wax, will desolve a bit when the new de-waxed shellac is applied and the wax will migrate into the fresh coat. POLY will still have a problem.

Also Matt, you said you already have several coats of shellac...

The best shellac finish is the THINNEST possible film that is flawless.

Applying a thick film of shellac is what causes the finish to alligator in the furture.

[Rick Lucrezi]

Hi Matt, just did the same thing. I called Zinsser and they told me their Bulls-eye sanding sealer could be applied over the waxy shellac and then lacquer or urethane over that. In addition, there is plenty of discussion about how finishers who have been doing it for 20 plus years say the amount of wax is not enough to cause adhesion problems and that most of the problems that are documented can be attributed to other factors, I personally have seen furniture with lacquer over waxy shellac with no problem. What most tend to agree on is that the "possibility" exist so is it worth the risk? Not to me for what I do but I am comfortable with the sanding sealer as a barrier. Hope this helps, and you can call zinsser direct.

[Prashun Patel]

The wax in shellac is emulsified - not dissolved. The solvent in shellac (alcohol) will not dissolve wax. It's the shellac itself that can dissolve the wax. However, there is such a small percentage of shellac in the top, dewaxed solution, and such a small amount of wax in the lower coat, that this is practically a very hard thing to do.

I know this because in my line of business, we routinely try to extract solvents and fragrances from candles and waxy systems. We typically use methanol precisely because it hates wax.

So, for my money, I believe a dewaxed shellac coat over a waxy shellac coat will be a good primer for any topcoat that doesn't use alcohol as it's solvent.