# water based poly over shellac?



## Cato (May 1, 2009)

I use shellac a lot in my projects and was considering Arm a Seal water based poly as a topcoat for a project in the works.

Would this product have a bad reaction with an undercoat of shellac?


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## 280305 (Sep 28, 2008)

I have done this, but I always apply a few coats of wax-free (dewaxed) shellac as a barrier between the usual shellac and the poly. Zinsser sells the dewaxed shellac as "SealCoat".

Just be sure to test it out on some scrap first.


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## CharlesNeil (Oct 21, 2007)

if your speaking of General Finishes " Arm R Seal" it not water base, but rather is a urethane oil, and an excellent finish, and will do fine over shellac , but you really don't need the shellac unless you just want to


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## Cato (May 1, 2009)

Chuck and Charles,

Thanks for the responses on this.

I ordered a can of Arm R Seal topcoat today. Apparently it is okay to use over dewaxed shellac.

Charles- when I was checking the Woodcraft site when I ordered they had the urethane and oil topcoat finish you speak of and a water based polyurethane that I ordered. The water based one I went with because it has a fast drying time.

"From General, these finishes are the best water based finishes we have ever used. Formulated to resist foaming and prevent sags, they won't run like ordinary water based finishes. Tack free dry time is only 15 minutes. Dry time between coats is 2-4 hours, so you can finish a project in short order. High Performance Polyurethane, HP, contains all the characteristics of a Poly/Acrylic blend, but also a UV stabilizer to protect it from breaking down in sunlight. This is, without a doubt, the best water based polyurethane on the market today."

Not sure if this is a new product from them or not, but thought I would give it a try.


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## Cato (May 1, 2009)

Oh, I forgot to mention why I was using the shellac.

My project is of mahogany and walnut. The mahogany test samples I have used looked best with either brown vintage maple dye or red mahogany dye followed by a couple of coats of dewaxed tiger amber shellac flakes.

Since it is a coffee table I need a topcoat to protect against moisture from drinks etc.


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## bobsmyuncle (Jan 12, 2011)

Just a bit of clarification. I am aware that Arm-R-Seal says (at least on the cans I have) "Oil and Urethane" However, this is just a bit misleading. It's like picking up a loaf of bread that reads "Wheat and Yeast Blend" This product is a varnish (produced by heating linseed oil and urethane resin, that then becomes a new compound we know as "varnish.") Then they thin the varnish with mineral spirits to make a wiping consistency.

The way to tell this is to put a puddle on some glass. In a day or two, you'll see a hard shiny surface. If it was really an oil-varnish blend, it would have some wrinkles around the perimeter. The more percentage oil in the recipe, the more wrinkles. Try the same test with Watco Danish Oil and you will see an oil-varnish blend (approximately twice as much oil as varnish, and a lot of thinner (about 2/3 of the can)).

But in either case (varnish or w/b acrylic) you should use a dewaxed shellac as the undercoat to avoid potential adhesion problems.


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## Milo (Apr 24, 2009)

Water based poly binds physically to material, rather than "burning" in chemically like old style finish.

Because of this, all you should have to do is rough up the surface of the shellac with a 3M "brillo" pad, then shoot or pad on the finish. Don't use steel wool, no metal and water allowed!

I did it all the time when I was in the biz…

Then again, I'm no long in the biz, so what do I know…?


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## MyronW (Sep 25, 2007)

I love shellac as an intermediary material. Shellac sticks to everything, and everything sticks to shellac. I either use the spray-on shellac from Zinsser, or mix my own so that I know it's fresh. Old shellac from a store-bought can will just make you mad.


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## zzzzdoc (Mar 6, 2010)

Interesting to see your dye choices. I've come to the same conclusion with Sapele, an African Mahagony. A combination of 50:50 Dark Vintage Maple and Red Mahagony TransTint dyes, followed by Amber Shellac makes for a gorgeous color on the wood.


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## KenBee (Mar 9, 2011)

I use Shellac on all my projects due to its ease of application and quick drying time.

ChuckV uses the the same process that I do which is very simple and produces excellent results and can be completed from start to finish in a days time. I also only use wipe on water based poly because in my experience I get better results than with a spry on poly.


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## MarkShultz (Nov 9, 2011)

Can I use an oil based poly over a water based sealer? am considering this because A) water based sealer was recommended b/c it wont darken the wood as much and B) the oil poly is easier to apply than water based. i'm a novice.


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