De-Waxed Shellac

A few notes on the chemistry of de-waxed shellac. July 3, 2008

Question
I used Zinsser shellac clear as a sealer over maple cabinets. I thought it was dewaxed, but it's not. I'm almost done with this project and topcoated most of it with Agualente and it looks great. The finish is sticking fine as far as I can tell. Any problems later? Should I just spray the doors the same way and hope for the best... and do something else next time?

Forum Responses
(Finishing Forum)
From contributor C:
Have you done any simple testing to know for sure how good the adhesion is? If not, try taking some duct tape and pressing it down on the surface and then pulling quick and hard to see if anything comes loose. Then you can also do a crosshatch test - take a razor blade and measure tape and cut lines 1" long through the coating and then the opposite way (making what looks like a grid or large X and O game) every 1/16", 10 lines each way altogether, and then use good cellophane tape or masking tape the same way you do for the duct tape and view the results. This will let you know if you have anything to be worried about in the future as to delamination/flaking/etc. You may have gotten lucky but you never know.

If more than 10% comes off on the hatch test, then it is not acceptable adhesion for my concerns. Definitely do something different next time. Zinnser seal coat.

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From the original questioner:
Thanks. I did that test and nothing comes loose even with Tuck tape, so I should be okay. For sure I won't do that again. I ordered some dewaxed shellac flaxes - thought I'll try that!

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From contributor C:
Dewaxed shellac still contains wax at under .2% levels. It is much better than the regular Zinnser at 5-6% wax levels, but still not as good as Zinnser seal coat. The main reason Zinnser spent all the r&d time on eliminating the wax was because people were having delamination and other problems using the regular Bullseye shellac, especially under polyurethanes and water base/solvent base pre- and post-cats. The shelf life on the product states the packaging date of the fresh seal coat and from there it will be good and usable for at least 3 years. The seal coat is not anywhere near as prone to esterification as the Bullseye due to them using non-esterifying alcohols. So it won't get gummy or non-drying like the Bullseye or other will do. Though I do make my own from scratch that do not contain wax and are not esterifying, it costs a lot of time and labor. Seal coat is the best we have on the RTU market and I'll stand by the product because I know the chemistry is sound.

I have not had any problems using fresh solved blonde so far, but if it was a critical application, I would use the seal coat unless absolutely necessary to keep the color lighter and not as orange/brown looking as the seal coat is over very light woods.