Shellac as a Sealer

Finishers clear up some confusion about waxed and de-waxed shellac used as a seal coat between different finish products. October 2, 2005

Question
I'm a little baffled by what I've been told about shellac today. I'm working on a kitchen cabinet job where the customer chose a stain sealer that has urethane added for the sealer. They also want a waterborne lacquer for clarity and speed (these are light stained maple to be finished on site).

I first thought, no problem - I'll seal the stain with Zinsser's seal coat as a barrier between the stain and waterborne finish. But I called the manufacturer of the stain just to check. They said no way - don't use shellac or lacquer on top of the stain. The shellac will strip the stain and the lacquer wont stick on its own. They said I'd have to use polyurethane or maybe a waterborne urethane would be okay, but let them know if it works because they've never tried it! Well, I'm kind of stubborn, so I called Sherwin Williams since I had planned on using Kem Aqua. The person I talked to also said not to use shellac, as it isn't compatible with urethane or lacquer.

This is going against everything I thought I had learned recently and I know I've used shellac between varnish and lacquer before without any trouble. Is there something I missed? I'm supposed to start finishing tomorrow. I did some samples this afternoon despite what I was told and will try adhesion tests in the morning. I'm hoping for some input from the best! Thank you.

Forum Responses
(Finishing Forum)
From contributor M:
The main reason coating manufacturers say "no" to shellac under their coatings is because some shellacs contain wax, which can effect adhesion, and could cause problems. Also, if you sandwich shellac between another coating, do not go back to shellac again, or you may get a bad reaction.


From the original questioner:
I'm off to work now, so that makes me feel better. The samples I did yesterday came out fine, too... both with and without shellac. The owner of these cabinets happens to be a builder, so I'll just show him the samples and let him make the call.

From contributor A:

The confusion is you are asking questions about straight Zinseer's BullsEye shellac. Their sealcoat shellac has no wax and can be used under, on top of, or as the stain base itself. Read the can and ignore all previous information. Sealcoat is compatible with all typical finishes used in woodworking. The only problems it poses is lifting alcohol based stains that are still ripe.

From contributor M:
Shellac certainly has its place in finishing, but that depends on the type of finishing you're doing. If your manufacturer tells you not to use it, regardless if it's waxed or dewaxed, and you use it, and you do have a problem, they're off the hook.

Think twice, finish once. Some finishers suggest it for coating over silicone contamination to seal the fisheyes in, others will tell you to use it as the sealer for water base coatings to prevent the wood grain from raising before the water base coatings are applied. Some will tell you to use it as a barrier coating to seal in a coating with problems.

When you have a finishing problem (in most cases, that you caused or did not prevent), you will eventually get desperate and try anything. Shellac is one of those things that you will try, and when you do, you're on your own unless the manufacturer and not the finisher tells you to use it.


From the original questioner:
I was telling them that I wanted to seal with shellac. I didn't mention any specific type. Should seal coat not be referred to as shellac?

I would've preferred to use a more compatible system all the way through, but for this job the customers really wanted a waterbased finish, but they also really wanted to use this particular stain, as it's manufactured locally and was highly recommended to them. I do realize I'll be on my own if there's a problem, but I also let the customers know what I was told and they had a "what the heck, let's give it a try" attitude, so I didn't do anything they didn't know about. So far, everything turned out beautiful. I've been giving my samples a rough time without any sign of a problem and it seems this was the perfect job for me to find out one way or the other.

I'm learning plenty and that's great. Two years ago I would have said no, sorry, we can't use that stain or we'll have to go with a polyurethane finish. It's nice to have plenty of options available and of course, plenty of knowledge to back them up.


From contributor M:
I suggest you always make up complete start to finish samples, which will allow you to learn the process. If you need to make any adjustments, you can do it on the samples. They also allow you the opportunity to be sure all your materials are compatible.

From contributor A:
Sealcoat is a new (2-3 years) patented, dewaxed shellac. The confusion comes when you tell someone that you are going to use shellac as a "seal coat". We are talking about a specific product - Sealcoat. I can't ascertain whether or not you are using Bulleye shellac or Sealcoat.

From the original questioner:
Aha! I used *Zinsser brand bullseye sealcoat*, not Zinsser shellac. I guess I haven't been making that clear. By the way, I think it's a great product! Thanks.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor A:
If you forget everything you have learned about commercial, toxic products you will realize that you can do everything with Shellac. You can prime, paint and stain. Moreover, you can do all these things on wood and cement.

For example: You can use universal colorants (Pro-Line or German-made Mixol) to tint B.I.N. (white shellac), and use it as paint. Apply the first coat, and if necessary, apply the second coat in 45 minutes - done! You can paint cabinets, walls, everything just like that.

Shellac as a stain - again, universal colorants in clear or amber shellac. Mix these to the color you want and put it on new or existing wood. Just clean the surface really well before applying it.

I'm a do-it-yourselfer, and use shellac for everything. It's easy, it's forgiving (if you make a mistake just wipe it off with cloth and alcohol and do it again), and more importantly, when it cures (1 hour) it's completely non-toxic. Bonus: if you are painting or staining plywood, which off-gases VOC for life (from the formaldehyde glues) you will in fact seal in all these gases for ever, thus making you environment much healthier.


Comment from contributor B:
As an experienced woodworker who turns bowls and makes high end custom cases, I can say that shellac is almost a good idea with very few downsides. Both clear and amber varieties add depth to a finish, and also have a pore-filling quality. Recently, I used clear 3# cut shellac for yet another reason: refinishing an unknown (or, in this case I simply forgot what was previously applied) finish. I had an old urn that had been chipped, and I knew if I put lacquer over polyurethane I'd create cottage cheese, so I lightly sanded he whole thing and sprayed a good coat of 3# clear, then topcoated with lacquer.

A couple of notes about shellac: heat (and hot sunlight, as a previous poster noted) reacts to some mixes, and bubbling is common if you try to speed up the curing process. Buffing it on you lathe is not a good idea, because the friction also causes heat, and you'll end up with globs of shellac. Keep plenty of 0000 steel whole on hand when you're using shellac.

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