Replies

1. 
   larryscabnuts | Dec 09, 2009 02:49am | #1

   "French polish it"?????? Maybe you will just have to fiddle with the shellac see how to build up the finish.

2. 
   DonStephan | Dec 09, 2009 03:55am | #2

   The answer probably depends on how thickly the shellac was applied wet.

   I've been told that thick layer of shellac more likely to alligator and check with time.  As an example, the recommendation was to brush only one coat of 2# shellac, or pad only three or four coats of full strength 2# shellac.

3. 
   davcefai | Dec 09, 2009 09:06am | #3

   I'm not sure if I understood the question properly but can you not first apply shellac to the top then tape the top, remove the tape from the bottom and build up the thickness there?

4. 
   HowardAcheson | Dec 17, 2009 01:02pm | #4

   This is one of the best write-ups I have seen about shellac finishing. It from a guy who does lots of restoration of old and antique items.

   QUOTE

   Applying a shellac finish is one part reading how (or watching a video demonstration) and ten parts practice. It is one of those processes in which you will one day reach what I call the "A-Ha" point in your journey and it will all simply fall into place. I would urge you to stick with the process and finish lots of test boards before you take the technique to a real project.

   I can give you this simple pointer as a place to start. Forget everything that you know about applying other finishes. In particular, that means forget about the concept of "coats"! Every time you apply another coat of shellac to an existing shellac film you significantly increase the probability of failure, both near and long term. This is especially true if you are attempting to pad on a shellac-only finish. Padding (in my view, the best way to achieve a high quality shellac finish) is actually a continuous process in which a single coat is applied in steps until the finish is refined to a very hard film and a high luster.

   I would also add (along the lines of changing your focus from "coats") that you need to change your view of what constitutes a good finish film. When we apply varnish, lacquer, or even water-borne finishes we think in terms of "building" the finish film. The best shellac finish is the thinnest film that you can apply consistent with good coverage and an even-depth film. One of my visualizations when I teach a class on shellac is to hold up a single flake of shellac (about the size of a quarter) and suggest that our objective is to dissolve this flake and then spread it evenly over the surface of our test board. Clearly, that is not possible; however, the image helps to reinforce the idea of a thin film. It helps students to think shellac and to loose the varnish or lacquer coat-building mind set.

   As further evidence of this "think thin" approach I will simply hold up the shellac finish on 200-year-old antiques. Those on which the shellac finish has remained largely intact (and there are many) are those on which the shellac film is quite thin. The ones that have alligatored are those on which the finisher built up a thick shellac film. In using shellac, you increase the amount of resin by mixing a heavier cut, not applying more coats.

   Finally, application of shellac is best accomplished by padding, not brushing. Attempting to apply more that the first application by brush leads frequently to uneven buildup and stickiness. Brush on the first application, sand flat and then pad on two to three more applications. Sanding should not be necessary unless you messed up during

   your padding.

   CLOSE QUOTE

1. 
   jonnieboy | Dec 18, 2009 05:23am | #5

   Howard,
   That's a great quote.
   Howard,

   That's a great quote. I like the perspective. It does change my thinking of "building up coats," and "thicker is better."

   --jonnieboy

5. 
   SteveSchoene | Dec 18, 2009 11:33am | #6

   The original poster's
   The original poster's question is, on it's face, basically a technical one with a quantitative answer called for.

   The biggest problem in figuring out the answer to the original posters question is figuring out how thick the shellac is applied. But that is highly variable. With a bristle brush a lot of material could be laid down, or with a mop type brush, a relatively large amount of material could be laid down, padding tends to lay down very thin films of material. I prefer to use a very fine bristle (Taklon Gold) water color wash brush that is some intermediate amount.

   To make some method of guessing, I'll assume that a fairly normal varnish type coat has a wet thickness of about 4 mils. That would typically give about a 2 mil dry coating, since the solids content would be typically close to 50% by volume. With that at a base I'd assume that 2 lb. cut shellac would be applied in thinner wet coats by almost any method.

   Ah, ha, I finally found my wet film gauge--it was hiding in some spray equipment I haven't used for ages. I made several tests of how thickly I applied Seal Coat using my Winsor Newton 580 Taklon gold brush. To be sure of erring on the high side, I made no attempt to apply an extra thin coat. It was applied on a metal substrate so there was no penetration to account for. A 3 mil thickness was the most I could generate without actually trying to create a puddle.

   But with the shellac that same wet coat would result in a dry film of 0.7 mil. To build a 1.9 mil thickness would require more than 2, and more likely 3-4 coats of 2 lb. cut shellac. And, this is why it is still just a guess, because it is so hard to know how any particular person would apply a single coat of shellac.

   There is another aspect to the question that has been addressed. There is certainly a school of thought that emphasizes the importance of applying shellac very thinnly. It is absolutely true that heavy wet films create problems quickly. To much solvent can do more than just meld the coats together, it can almost completely redissolve lower coats, and the smallest disturbance can cause shellac to "rumple" and make a heck of a mess.

   But, this potential problem doesn't mean that the total dry film thickness needs to be kept to completely minimalist levels. The argument usually runs along the lines that too much shellac will alligator, and is often cast in a setting of looking at antiques. But it is pretty difficult to make that argument solidly, since to do so would have to be based on a systematic study involving a number of pieces with detailed analysis of the multiple layers and composition of the finishes on them. I don't have access to a serious research library to dig out those articles, if they have been done. What looks like a "thick" alligatored finish may have only some shellac. Spirit varnishes with even more brittle resins, such as sandarac may have been used. Old oil varnishes--including rosin as resin may be in some layers, and multiple "treatments" of concoctions such as linseed oil and vinegar may have been used over the years. It's likely the interactions between finishs made of different materials that cause alligatoring more than just thick coatings of a single material.

   And, also remember that if shellac is rubbed out--and it is an idea finish for rubbing out--a substantial portion of the dry film thickness is likely to be abraded away.

   I'd have absolutely no qualms in using 6 or 8 applications of 2 lb. cut shellac if applied in relatively thin films by padding or with the low reservoir brushes. Substantially more applications could be just fine if any sanding, either for leveling while proe filling, or if rubbing out is used.

1. 
   PhillipB | May 17, 2019 10:28am | #7

   Hello Steve,
   I came across your comments while doing some research on shellac. If you have a moment, would you please comment so I can ask you a few questions?

   Thank you,
   Phillip