finishing with W/B poly over sanded shellac

I have often wondered this myself. I have also used the Zinsser shellac and in a pinch, did as you have done and sanded and applied poly over it. As with you, it ‘worked’ but I also wondered about the longevity of it. I would think that once it adheres to the previous coat, we would be OK. I was also under the impression that as long as the under coat is cured, that most anything is possible. (I thought I had remembered reading this somewhere, and I also have heard of using poly over well-dried oil paints – although I don’t know how sure I am on that one.)

I will be watching this topic with interest. Great question.

Sheila

-- Designer/Artist/Teacher. Owner of Sheila Landry Designs (http://www.sheilalandrydesigns.com) Scroll saw, wood working and painting patterns and surfaces. "Knowledge is Power"

as long as the under coat is cured, that most anything is possible.
That’s a good point,I wonder if the first time I failed was because the shellac wasn’t cured properly,IIRC I only waited for an hour or so for the shellac to dry before putting on the poly but now I would sand any surface before applying water based poly.

-- Ken from Ontario

I’ve done quite a few pieces with ordinary poly over sanded shellac (not dewaxed), and have never had any problems at all with adhesion or longevity.

I think I read in Bob Flexner’s “Understanding Wood Finishing” that as long as the under coat is cured it is possible to use anything over it. That is much longer than an hour to be sure and it may be why it was unsuccessful. :)

Here is the link to the book:

http://www.mohawk-finishing.com/catalog_browse.asp?ictNbr=292

It is a good one. ;)

Sheila

-- Designer/Artist/Teacher. Owner of Sheila Landry Designs (http://www.sheilalandrydesigns.com) Scroll saw, wood working and painting patterns and surfaces. "Knowledge is Power"

I wonder why waxy shellac is used at all?
For me, dewaxed is a far better shellac because of its pretty much universal compatibility…

-- He who dies with the most tools... dies with the emptiest wallet.

I usually don’t dewax shellac and I have not found
varnishing over it to be a problem.

-- http://lawoodworking.com

I used Zinsser Bullseye sanding sealer (dewaxed shellac) under Minwax Polycrylic before with out any issues, but I haven’t done that that often.

-- Mos - Twin Cities, MN -- Stanley #45 Evangelist - www.youtube.com/MosquitoMods

Nite walker,I love the amber color shellac has and warm glow it gives ,also when diluted is a good sealer.
I also have not found any short term problems with adhesion but I don’t know if down the road I will have cracking and peeling with this water based poly is applied over shellac.

-- Ken from Ontario

I have to beg the question, “Why”, Seal coat is on the same shelf, its dewaxed, I do this for a living, I can’t afford to buy cheap tools or take chances. Why would you even conside the risk, sorry but to me it makes no sense whatsoever. !!!!

Aside from loving the amber color, shellac serves no purpose that the first coat of any finish doesn’t. But it does complicate the process, and cost more.

-- Clint Searl....Ya can no more do what ya don't know how than ya can git back from where ya ain't been

Wax is inherant in shellac. De-waxed shellac has had it removed. I agree with Charles that if you are using it as a seal coat, you should just buy the de-waxed version. I have found that in French polishing, I prefer the waxed version as it seems to apply better and easier from an application rubber. Other than that, I used the dewaxed version. You may have had the wb poly adhere after sanding because you gave it a more mechanical “bite”, but I don’t think I would trust it in the long run. Wax and wb poly do not get along very well together and it may eventually lose bond.

-- Paul, Las Vegas

The problem isn’t actually with the shellac, it’s with the polyurethane (or urethane) resins used in the finish. While they have a property of adding scratch resistance to a finish, they also add a problem with adhesion; it doesn’t even stick to itself very well (that’s why you scuff sand urethane finishes before recoating). You can topcoat waxy shellac with (almost) anything else and not have to worry. The wax does add to the moisture resistance properties of the shellac, so if used by itself waxy may be best. Regardless of your experience, I agree with some others…it’s not worth the risk: use dewaxed under urethanes.

-- Our village hasn't lost it's idiot, he was elected to congress.

You can use poly to seal and if you like the amber color, place the cured poly in the sun and you get the same effect or pretty close to it.

-- earthartandfoods.com

I sincerely appreciate all the replies to this thread,understand all the reasoning behind your opinions and the warnings but it looks like no one has had a solid first hand experience if this method in a long term would fail.

Some of you a asked why not just use dewaxed,others ask why use shellac at all,”it serves no purpose ” or this method is bound to fail ,you are all most likely right but in the absence of any evidence whether there will be a bonding issue if poly is used over regular shellac,(please forgive me for saying that)I am not convinced.
As our respected friend and woodworker in his, non scientific but acceptable in(in my opinion at least) test says : ”It is some what of a myth that may be in some situation with some polyurethane,on some shellac on some species of wood,may be some day some one some where would have a problem with the binding of the polyurethane”(near the end of the clip,15.03 mark)
http://www.youtube.com/watch?v=7kCnmW6mKCM
Again I understand why some would question this method or caution against it but I(respectfully) just wanted a direct answer to this question,backed with some direct experience/ evidence.

I should add,the SEAL COAT product is not readily available in Canada,neither is denatured alcohol,both items could be ordered though.
I have huge can of regular shellac .

-- Ken from Ontario

Regardless of some opinions, I use the Zinsser Seal Coat as a primer for most projects. As long as the shellac is de-waxed, you should have no probs with any finish you choose.
There are soooo many apps for the shellac, and it sure has helped me with quality finishes.
Just my view.
Bill

-- bill@magraphics.us