Replies

1. 
   Tao | Apr 01, 2005 10:25pm | #1

   This from George Hoyas at Zinsser.  These are excerpts from a much longer exchange:

   ........ As for the use of shellac as a sealer under oil-based polyurethanes, trade use data for the past twenty years or more militates strongly in favor of shellac. Indeed, the highest sales numbers we have for our pre-mixed dewaxed shellac sealer are to the flooring trade, where flooring contractors use it with considerable success under oil-base polyurethanes because it dries so fast that the first coat of polyurethane can be applied in under one hour. To date we have not received a single report alleging incompatibility between the sealer and the topcoat........

   ..........As for intercoat adhesion failure (“separation of layers”), whether of shellac over another finish or of another finish over shellac, the culprit is always either an intervening layer of contamination in the former instance or the inability to develop chemical adhesion in the latter instance. I have yet to see any polyurethane – either water-based or alkyd – fail to develop adhesion to dewaxed shellac............

   ........ If the reference is to flake shellac, rest assured that there is no difference in shelf life between waxed and de-waxed grades. Pre-mixed de-waxed shellac does have a longer shelf life than the regular waxed product, but this has nothing to do with it being refined (i.e., wax-free) and everything to do with it being made from a patented process. It is packaged no differently from the regular clear and amber shellacs; however, it is not nearly as well distributed in the marketplace as the other shellacs. This, too, may change, as it appears that Home Depot will be carrying pre-mixed dewaxed shellac in another month or two.....

   .....Actually the presence of wax has nothing to do with the hardness of the dried film. One or two coats of paste wax will not only improve the scratch resistance of a dewaxed shellac finish, but will also provide excellent resistance to water-spotting.....

   I think what it adds up to is that you can pretty much use dewaxed shellac under or over just about anything as long as the film is cured, and that shellac with the wax still in it is a little less clear, but a tiny bit more durable as a topcoat.

   Michael R

    

2. 
   HowardAcheson | Apr 01, 2005 11:03pm | #2

   In addition to everything the Woodwiz says, dewaxed shellac is more watervapor resistant and it is clearer.

   All that said, there is no reason not to used natural shellac (non-dewaxed) unless you plan to overcoat it with oil based polyurethane or any waterborne finish. Natural shellac works just fine as an undercoat for standard varnish, lacquer or paint.

   Howie.........
1. 
   MarkRD | Apr 01, 2005 11:24pm | #3

   This is a bit of a tangent, and perhaps someone can explain it.Years ago, I had a strange discovery with shellac,I had a can that had been lying around for some time, I used it on untreated wood. I left it alone for some time but it stayed tacky. So I figured it was trash.I put the open can outside to let the fluids evaporate. It rained a bit while the can was outside. Came back to the can a week later - the can was literally full of dead garden slugs. Really quit gross and amazing at the same time. Seems that the slugs were attracted to it, Climbed into the can and drowned or were killed by the solvent.So don't throw out that old shellac, put it in the garden to kill the slugs.Strange.(This is not an April fools)

   Measure it with a micrometer, mark it with chalk, cut it with an ax.

3. 
   AlbionWood | Apr 01, 2005 11:34pm | #4

   I'm not an expert, but I can answer that last question: You can apply almost anything over Dewaxed shellac. That's why it is frequently recommended as a sealer coat. The other great thing about it is, it will dry over (and adhere to) almost anything - so it is a great way to seal off contamination in older wood.

   Regular (waxy) shellac is not as good for sealer, as the wax can interfere with adhesion of some topcoats. I use regular shellac as a final finish. The wax content makes it much easier to sand. I build up a good surface film, say four coats of 2# cut, then sand it flat and level. The waxy shellac will sand very fast and easily if it is fully dried. Then you can either pad on a final coat of shellac, for a gloss finish, or apply wax and buff to a semi-gloss.

   The premixed shellac sold by Zinsser is a waxy formula, so it is not so good for a sealer. You pretty much need to buy flakes and mix your own dewaxed shellac. [Edit: I see from the other messages that Zinsser is coming out with a retail premixed dewaxed shellac. Great news!]

   "Everything should be made as simple as possible, but no simpler." A. Einstein

   http://www.albionworks.net

   
   

   ---

   Edited 4/1/2005 4:39 pm ET by AlbionWood

1. 
   HowardAcheson | Apr 02, 2005 03:17am | #5

   >>I see from the other messages that Zinsser is coming out with a retail premixed dewaxed shellac. Great news!Not new news. Zinsser came out with their Sealcoat about three years ago. Go to: http://www.zinsser.com/product_detail.asp?ProductID=72While they market it as a "sanding sealer", it is a 100% dewaxed 2# cut of blond shellac.Howie.........

1. 
   Rich14 | Apr 02, 2005 04:57am | #6

   And it's formulated to have a shelf life far in excess of the typical 6 months for the home mixed kind. It's prolly a better deal than mixing your own. But I'll never stop doing that as long as I can buy shellac flakes.Rich

2. 
   AlbionWood | Apr 02, 2005 07:20am | #7

   Cool, I will look for that! Thanks.
   "Everything should be made as simple as possible, but no simpler."  A. Einstein

   http://www.albionworks.net

1. 
   WillGeorge | Apr 03, 2005 02:33pm | #8

   Ohhhh.. I forgot to thank you all for the replies.

   Well, thanks!