Regular or dewaxed shellac?
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is an appropriate primer coat. May 22, 2002
Q.
Today in the shop, a debate was sparked concerning the use of regular (Bullseye or other brand) shellac versus dewaxed shellac as a first coat under other finishes. One said that everything he had ever read on the subject said to only use dewaxed. There were many books and web writings by noteworthy authors cited. The other said that all he had ever heard from local finishing professionals was that dewaxed is not at all necessary. Also, he cited his 25 years experience and the generations of experience from other local finishers wherein there has never been a finish failure attributed to using regular old Bullseye shellac - no decanting, maybe stirring, maybe not.
After a bit of discussion, only one thing was agreed upon. Neither had ever heard of an actual finish being/going bad due to wax in shellac. Anyone ever have a finish that you put over top of regular (wax still in) shellac go bad? Is this dewaxed thing for real?
Forum Responses
Why do you want to use a topcoat like Magnalac under another topcoat that is water base?
From the original questioner:
You're skipping to the next issue, but we'll get a head start anyway. The rationale behind using Magnalac under WB poly is that is seals the grain sufficiently to prevent the WB poly from raising the grain. The rationale extends that WB poly (specifically SW wood classics) is a tougher, more durable finish than lacquer, yet is more repairable/replaceable than something really tough, like conversion varnish.
I've never dewaxed shellac and used it much under NC lacquer, vinyl sealer and pre-cat acrylic lacquer (without vinyl sealer). Always scuff coated the shellac before applying finish over top of it. Never had a bond failure.
I'm of the opinion that most adhesion failures (aside from absolute incompatibility between finishes) are a result of a failure to thoroughly and completely (that means every square millimeter) provide a scratch pattern on the surface before applying subsequent coats.
Another area that seems to be common for adhesion problems is at the edge. Often, one neglects to "ease" the edge properly. A sharp edge just doesn't allow for the material to flow around the corner and hang onto itself.
It could be that the real culprit is pilot error, rather than poor finish products or chemical incompatibility between finishes. How many ways can you think of that might cause one finish not to bond to another finish, aside from incompatibility? We all know that shellac or common NC lacquer on top of itself will burn into the preceding coat, no matter how old the finish is, provided there are no contaminates between the two. Recoat windows are important with some finishes and I'm willing to bet there are some workers that actually don't read and follow printed directions. I can't count the times I have witnessed people try and recoat polyurethane after a day or longer of drying, without sanding between coats. Then they will sand it like crazy before the final coat and wonder why it seems to be wearing down in layers. I suppose the easiest thing to do is blame the finish, eh?
From contributor G:
I've sprayed WB lacquer over Zissner non-dewaxed shellac with no problems. It's been at least six years now on several chair batches and no callbacks. The pale and un-contrasting grain appearance of WB doesn't hold a candle to conventional oil and lacquer finishes, but with shellac or NC you can get the advantages of both, just 1/2 of each. The problem I see is mixing the two finishes in the same gun, hoses and pot.
From contributor V:
"How many ways can you think of, that might cause one finish not to bond to another finish, aside from incompatibility?"
Herein is why I would avoid using shellac containing wax under a different topcoat. If an adhesion problem occurs, there is one less thing on my list of suspects if I have used a dewaxed shellac.
I have shot a lacquer over one brand of shellac several times with no problems. On two occasions, I had an adhesion failure. So I got rid of that brand. I may not have noticed the adhesion problem, but for the job hanging around in my shop for several weeks. After walking by it a hundred times or so, I noticed unusual light variations in this old walnut sideboard I had refinished.
From contributor R:
Contributor D has it dead on. Using dewaxed eliminates potential problems. A 'waxy' shellac may not ever cause a problem, or it may down the road - it is hard to tell. Waxy shellac isn't like Teflon - stuff sticks to it, though not quite as well. I too have seen minor adhesion problems with waxy shellac.
There is no downside to using dewaxed shellac. It doesn't cost much more and it's not any harder to obtain or use. When available, I always use de-waxed shellac.
The only advantage to using Zinnser is that it comes in a can. E.g. ready to brush. Mixing your own shellac takes a tad bit of planning.
From the original questioner:
Contributor G, haven't tried WB lacquer. Use a good bit of Magnalac, though. I'm definitely with you on WB making some stuff look terrible as compared to solvent based finishes. We almost always hit projects with shellac or lacquer for both grain raise prevention and that most beautiful look that I haven't seen without it under a WB finish. Not that I'm an expert, or that I've tried all brands - I haven't. Some may do it, but the ones I've seen don't. Never had a problem with equipment. We clean the solvent based stuff out with lacquer thinner and then clean the gun with warm soapy water before switching guns. Or, if real busy, sometimes we'll have two guns set up. We use just a cup gun anyway, so the hoses/pots are not an issue for us.
Contributor V, I'm the guy who would use the de-waxed. Specifically for the reason you said. We've all had to strip and re-do projects. There's so much money lost on that, it could make you cry. I figure the extra few dollars for dewaxed is not worth the shop time to figure out if you have a problem, let alone begin the terrible process of fixing it. When I do work by myself, I use dewaxed.
From contributor D:
All of this discussion is irrelevant. Zinsser, after 100 years, has finally introduced their dewaxed Seal Coat Shellac Sanding Sealer. Simple, easy, quick and pre-dissolved in a can. Case closed.
Try to find it on the shelves, though. Even sales reps don't have a clue what it is or where to find it.
From contributor D:
It's readily available here in Arizona at my local Kelly-Moore paint store.
I'll play the devil's advocate. I've got a coating failure. I used, say, SW products as a topcoat. I am talking to the SW rep. My finish schedule? I sealed first with someone else's shellac before applying your topcoat. What does the rep say? It doesn't matter if that was the real reason for the failure - you are screwed. When I have to use products from different suppliers to do a specialty finish, I always do a sample and personally test the hell out of it, especially for adhesion. I have done adhesion tests with lacquer over shellac and I am not impressed.
One has to be careful when describing their experiences with waxy shellac. I make an 8oz liquid sample of every lot of shellac I sell, so I have trace-ability for a lot. I also deal with a vendor that can supply an assay immediately or upon request if one does not exist for that lot. Sometimes the Lemon flake that is used to make Bullseye has a particularly high wax content and the lots I buy are no exception. Zinsser goes to great lengths to blend the Lemon flake used for Amber Bullseye so that lot differences are minimized - but still there can be differences. If you use the Clear Bullseye, you're apt to experience more consistency from can to can. I stick to low-wax content shellac lots for the few waxy pre-mixed shellacs I offer, because it seems prudent to do so and I can be picky.
I totally agree that waxy shellac is always acceptable under certain coatings. A plain oleoresinous varnish like Waterlox can always be put over waxy shellac and has been for decades. As pointed out, though, there's certainly no harm in buying and using dewaxed shellac exclusively to keep it simple.
There are some good reasons not to intermix certain coatings. Scuff sanding, as one contributor pointed out, is a good "just in case" practice, in my opinion.
From contributor R:
Contributor D, I must disagree with you. There is simply no material advantage to Zinnser (waxy or not) over mixing your own shellac. In my experience, the Zinsser product doesn't form as hard a finish as the shellac I mix myself. It also doesn't seem to have the clarity or tone of mixed shellac. The Zinnser product is also more than simply shellac and alcohol - it has additives to extend its shelf life. It brushes and sprays noticeably different from mixed shellac. The only advantage to using Zinnser is that it comes in a can - a ready to use 3lb cut. This is pretty spiffy if you don't use shellac much. It's not better in any other way to mixed shellac.
Mixing your own shellac has several advantages:
1) You know when it was mixed so you know it will dry hard. No guessing, no hoping.
2) You have many more choices than basic blond and amber from Zinnser. Shellac vendors sell many types of shellac from super blond to stick lac. Many types are available in waxy and dewaxed types.
3) Mixing your own shellac is cheap. I buy Russ's 200 prof 5 gallons at a time. In this quantity, it's cheaper than the cruddy denatured alcohol from Home Depot or Lowes. Dry shellac is cheap.
4) Using Russ's anhydrous 200 proof alcohol means you know that nothing is left in the dried film but shellac.
5) I use the fact that I hand mix my own shellac as a marketing tactic. It's more of a purist approach and helps sell product and get better prices.
From contributor D:
The Seal Coat is not the same as the regular clear Zinsser, which is waxy. It's crystal clear (no doubt bleached) and it's a 2# cut. It has a guaranteed lifetime of 3 years from the date stamped on the can and it is guaranteed to be completely dewaxed and it sure looks like it is when you open the can. I buy shellac from Russ all of the time, too. And in my opinion his alcohol mix is the best. But, if you're looking for some dewaxed shellac and the paint store down the corner has it, it certainly is a good thing rather than waiting for the UPS man to arrive with it from the Frozen Tundra.
From contributor R:
I think we're in agreement. I do have a can of Zinnser specifically because I needed some and ran out of Russ's orange. I know their guarantee is 3 years, but I just don't believe it. To me, using shellac for a fine finish simply means mixing my own. The only disadvantage is waiting on UPS.
I believe that only products containing polyurethane are affected by the wax in shellac. Unfortunately, many varnishes contain poly without the manufacturer making that clear.
From the original questioner:
I think based upon the body of responses, I will continue to use Russ's dewaxed. Based upon his positive experience, my friend will continue to use the stuff out of the can.
