Shellac as a sealer? It’s all just hype

28_bob_fexnerYou’ll hear shellac tossed around a lot as the “best” sealer, mostly in woodworking magazines targeting amateurs. I’ve come across many professional finishers, however, who believe they should be using shellac rather than the finish itself, a sanding sealer, vinyl sealer or a catalyzed sealer for a first coat.

With only a few exceptions, there’s no reason for anyone to use shellac under another finish. Shellac has been totally overhyped as a sealer. Here’s the story.

History

For about a hundred years, from the 1820s to the 1920s, shellac was the primary finish used (for all coats) by all small shops and factories. In the 1920s shellac was replaced in factories by lacquer for two primary reasons: shellac resin (from bug secretions) is a commodity product that was going up in price as demand increased, while lacquer was going down in price; and lacquer thinner (a blend of solvents) makes lacquer much more versatile in different weather conditions.

Shellac continued to be used by painters and floor finishers working inside buildings and by amateurs until the 1960s. Then three things happened that almost totally ended shellac being thought of as a complete finish:

• Oil-based polyurethane became available. It was originally marketed as a “no-wax” floor finish, meaning that it was durable enough to resist scratches without being waxed (as was necessary with shellac). Through the years, polyurethane became the most popular wiped and brushed finish for everything.

• Homer Formby began marketing wiping varnish (varnish thinned about half with mineral spirits) as “tung oil” through TV infomercials and shopping-mall and antique-club appearances. He did a masterful job, creating a large market for his finish and for other brands as well.

• Woodworking magazines began promoting Danish oil (a blend of linseed oil and varnish) as an easy-to-use finish that protected the wood “from the inside.” The finish became very popular with amateur — and some professional — woodworkers.

Shellac is much more difficult to use (see below) than these three finishes, so it almost disappeared as a finish except in a few niche markets such as French polishing and handmade reproductions of antique furniture.

Companies supplying ready-to-use shellac disappeared one after another until only Zinsser remained. Seeing its market disappearing, Zinsser (Bulls Eye), with the help of some woodworking writers, turned shellac into a sealer, even introducing a dewaxed variety (SealCoat) that was marketed for use under polyurethane.

But here we return to the central question: Why not use polyurethane itself as the sealer? It “seals” the wood perfectly well. Why use shellac under several coats of polyurethane — or under any other finish? The answer is to solve a problem.

Shellac has wonderful blocking properties, better than any other finish. It blocks silicone contamination, which causes fish eye, odors (for example, from smoke or animal urine), and residual wax extremely well.

22_cutting_edgeShellac also blocks the resin from pine knots and very oily exotic woods, which can slow the drying of lacquer and varnish significantly.

But notice that the first three situations are all refinishing problems, not new-wood problems, and the last is rare for professional finishers.

So for almost all new-wood situations, we come back to asking why use shellac at all?

Types of shellac

Not only is there no benefit to using shellac as a sealer in most situations, there are good reasons not to use it. Shellac is a difficult finish (or sealer) to use.

The first reason is the confused naming. Before you even get started, you have to learn the different types of shellac.

In liquid form there are clear (actually pale yellow) and amber shellacs. Until about 20 years ago, when Zinsser changed the names for marketing purposes, these were labeled “white” and “orange.” “Who wants orange furniture?” the Zinsser rep explained to me to justify the name change.

There’s also dewaxed shellac, which is more expensive. Should you be using that? Or will the shellac with its natural wax still included work just as well?

In flake form, which you dissolve yourself in denatured alcohol, there are many more varieties: blonde, superblonde, lemon-yellow, orange, garnet, button, ruby, extra dark and more. These names all refer to the color, ranging from pale yellow to very dark orange.

A second issue is the way solids content is measured. It’s not the standard percentage method used for all other finishes. It’s “pound cut” — the number of pounds of shellac resin dissolved in one gallon of alcohol.

Clear and amber liquid shellacs are three-pound cut. Dewaxed SealCoat is two-pound cut, which is no longer listed on the label. Though conversion to percent solids is possible (so you can predict the total build of your finish), this is another difficulty you have to overcome.

A third issue is shelf life. Once shellac is dissolved in alcohol, it begins deteriorating (more rapidly in hot temperatures). It takes longer to dry and it doesn’t dry as hard. After the shellac has deteriorated a few years in the can, the finish you apply over it may wrinkle.

Shelf life is not a problem if you dissolve your own from flakes (an extra step) because you know when you did this. But it is a problem if you buy already-dissolved shellac. Zinsser has stopped putting the date of manufacture on its cans. So you can’t know how well the shellac you’re using will perform without calling and finding someone who can translate the stamped lot number. You don’t know how long the shellac has been sitting on a store shelf or in a warehouse.

A fourth issue is blushing. You can control blushing with products that thin with lacquer thinner. Just add some retarder. It’s not so easy with shellac because there aren’t retarders available.

A fifth issue is ridging. Unless you thin shellac a good deal, it has a tendency to ridge at the edge of brush strokes and orange peel when sprayed.

If all this isn’t enough to make you question the wisdom of using shellac as a sealer when you don’t have one of the problems mentioned, consider that shellac is a relatively difficult finish to sand. It gums up sandpaper unless applied very thin.

Bottom line

You might conclude from this discussion that I don’t like shellac. This would be wrong. I like shellac a lot.

But my background is refinishing. Shellac is a wonderful tool for solving refinishing problems. It’s also great as a finish when you want to replace an original 19th century finish with the same thing.

But there’s rarely a reason to use shellac in a factory or cabinet shop making cabinets and other objects out of new wood.

Bob Flexner is author of “Understanding Wood Finishing” and “Flexner on Finishing.”

This article originally appeared in the September 2012 issue.

Comments (15)
15 Saturday, 07 June 2014 20:31
Gary Klifman
Hi Bob, I am a log furniture maker in CO. I use 2" pine slabs for picnic table tops. The knots don't seep until we apply the stain (Sikkens cetol S.R.D. in the teak color).
Then after a few days or weeks in the sun they seep sap.
We don't use top coats such as poly or varnish as it will surely peel with our harsh UV's. Any suggestions on how and what to use to seal these knots with? Appreciated, Gary
14 Sunday, 04 May 2014 08:39
Richie
What do you recommend (shellac or another material) to seal and protect the spruce face of my Oud stringed instrument? The face needs to remain flexible enough to sustain vibration -- for tonal quality purposes. Any recommendations, please?
13 Wednesday, 26 March 2014 22:46
Tony
It's funny that the guys building stringed instruments couldn't disagree with you more. With that group, they swear by dewaxed shellac as a seal coat to promote adhesion when water based clear coat will be used, or over an epoxy grain fill, where nitrocellulose lacquer will otherwise fail to properly adhere.
12 Friday, 14 March 2014 00:10
Hobo
I am staining all of my trim work in the house I am building. I am using alder and it really blotches. Some people like that, however I don't. I used the Zinsser's Seal Coat 100% wax free and thinned it with denatured alcohol at a 1:1 rate.
It is amazing at how the blotches do not come through. Keep in mind an oil based stain will not penetrate as deep so the color won't be as deep. Using a gel stain instead can help with that.
11 Wednesday, 05 February 2014 22:49
Andrea
I have used shellac flakes before to refinish my antique dinning room table. You can do it verry successfully if you do very thin layers and use the foam brushes. I just bought a whole pack and threw each brush away after using it for one layer. For everyone making comments or questions don't use shellac if the thing you use it on is exposed to lots of water. Shellac discolores when exposed to moisture. do not use pre mixed shellac from big boxed stores for anything it is not good stuff.
10 Friday, 31 January 2014 01:20
James Lindgaard
What I am wondering is how well does it seal against water. It won't be visible in use. And when I say seal against water, it will have constant exposure to it.
9 Tuesday, 10 December 2013 17:40
Rhea
Hi there!

I was thinking of using shellac to seal the knots on pine t&g panels that I want to install in my bathroom that we are renovating!

Is shellac still good for this purpose??
Should I paint the whole board front to back, even though one side will be facing the wall?
Will I still be able to paint the boards white afterwards?

Thanks so much!!

Rhea
8 Sunday, 27 October 2013 15:39
Lil Bernstein
I want to have a wood kitchen table that I can use without worrying about heat and water marks. Do you know if any manufacuters do this or would I need to purchase a wood table and then apply shellac or polyurethane? What do you suggest?
7 Monday, 21 October 2013 17:00
Mindy cook
Hello Mr. Flexner! We just recently bought a 1955 ranch home. I am desperately trying to match one side of paneling to the original finish. I have had professionals out and no one can tell me what they used. I have read all of your books. I believe this finish to be amber shellac, but it is not glossy at all! From everything I have read you cannot apply a satin finish over the shellac so what do you do to get a very matte satin finish on shellac??? Also the man at the store tried to sell me amber dye stain would that work???? I need help and if anyone can it is you. Thank you so much for your time!
6 Monday, 23 September 2013 11:25
mike volo
I used Buyll's eye clear shellac to paint my plywood subfloor and still smells like shellac even after two weeks. very disappointing of this product. I was told the shellac smell will disappear in few hours...
5 Wednesday, 04 September 2013 18:29
Mr. T. Minnesota
Bob,
I am about to refinish an old end table made by Knoxville Table and Chair Company for my son in the Twin Cities. Have used many different types of finishes but wanted to experiment with no wax shellac. I plan to use Watco oil base stain and finish with shellac. Not a major project, just a retirement project. Any suggestions?
Mr. T. Minnesota
4 Tuesday, 20 August 2013 15:32
Craig
I use wax free shellac exclusively as a ground in violin finishing and shellac gives acceptable grain depth when used beneath water based lacquer, again with musical instruments.
3 Thursday, 09 May 2013 18:20
Ken Tubman
I agree with your article. I use it as a mild finish on my indoor projects.
I builds Arts & Crafts type pieces. I like the natural colors of most woods.
I just finished my Limpert book stand made from Paduc and Canary woods.
A soft rut out with mineral oil and pumice powder gives me a smooth feel and finish.
This way,I don't have to tung oil the stand every six months.
check out shellac.net. I purchased from them and got great pricing on my flakes.
2 Tuesday, 16 April 2013 16:27
John
Great article! I have a question you might offer some insite. My daughter is getting married in an out venue in two weeks. Last years the venue installed seating constructed with 8x8 PT pine timbers. Looks awesomw, but a recent planning visit revealed that some of the timbers are oozing sap. I was thiunking about cleaning sap with turps and applying shellac in hopes that it will slow the sap enough to not wreck our guests clothing. Any thoughts on this?
1 Saturday, 09 March 2013 17:41
Nick Buffone
Bob:
This was a very helpful article. I am building two base cab's out of Red Oak for a restaurant. Only one side of the four sides will be exposed due to where they're being placed, but I still want to seal them. My thought on shellac might not be good.
I have no spray equipment, but does wipe on or brush on polyurethane seem like a better plan?

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