Shellac Issue

shankahoe | Posted in Finishing on September 17, 2020 11:10am

So please be gentle folks, as I’m newish to woodworking and have officially used shellac for the first time. I, however, did purchase the zinnser bullseye clear shellac you can buy at the big orange box store. My finish generally looks decent, pre rubbing out, but I noticed After I sat a dry rag on the surface a day or two after drying, when I picked up the rag, there were tiny indentations left on the surface where the rag made contact. I then tried laying a small rubber covered Allen wrench on the top for 15 mins, and after picking up there were two markings left on the surface, as though the shellac is almost being pushed out of the way, like a semi liquid. But the finish is dry to the touch and has been for days. I have been putting numerous thin coats (at 6 so far), before I noticed this. I waited another 2 days and tried again, and it still did the same thing, I made sure I thoroughly mixed the shellac and everything while applying, sanded down with 320 after the third coat to level out and started again and waited at least a few hours if not longer between really thin coats. Any ideas where I may have went wrong?

Replies

Rob_Sp | Sep 17, 2020 12:03pm | #1
What you did wrong was not to check the date of manufacture. Old shellac will not dry to a hard finish.. Shellac has a shelf life, Zinnser claims 3 years although I would not use it anywhere near that old. Don't feel bad, because they don't make it easy. They used to stamp the date of manufacture on the can, but now they use a code you must decipher. I would not purchase anything not made within several months to maybe a year. You can test by putting a drop on the lid and letting it dry then check the hardness with your nail. You will need to completely strip the existing finish and start over with a fresh batch. Fortunately this is easily done with the alcohol thinner. Best bet is to mix your own with fresh flakes. Here is a link where you can buy, also a lot of info.
http://www.shellacfinishes.com/
john_c2 | Sep 17, 2020 12:13pm | #2
I doubt you did anything wrong. Shellac has a shelf life. If it's too old, it will never cure completely. The best way to see if any finish is fully cured, take some fine sandpaper, say 320 or so, and lightly sand some finish. If you get a whitish dust, it should be fine.

Zinsser does not put an expiration date on cans -- though they used to. The last I checked, they put a coded manufacturing date on the lid. To decode it, it will say "LOT" followed by a string of numbers and letters.

The first space is a letter, referring to which manufacturing plant made it. The first digit after the letter is a number, the last digit of the year. The next number is the month, but with "O", "N", "D" for October November and December. The next two digits are the day of the month. The final digits are internal manufacturing numbers.

Today's date would be rendered "LOT S0917xxx" Christmas day would be "LOT S0D25xxx"

Zinsser used to claim their shellac would be good for three years. A lot of woodworkers said it was closer to one. Longevity depends on if it is unopened, humidity, temperature, etc.

My guess is you have old shellac.

PS. Zinsser Sealcoat shellac is dewaxed, and lasts longer than the clear and Amber. I don't think they even put the date code on those. But it's harder to find, and big box stores don't carry it. Too bad, as it's superior to the other stuff.
weymouth2 | Sep 17, 2020 01:01pm | #3
I'm newish too and highly recommend mixing your own. You can make it in small batches, so no need to worry about it going bad. It seems intimidating at first, especially if you read a book on finishing (which can be wicked confusing). But it's really simple. Buy the flakes. Buy the alcohol. Combine.

I bookmarked this and refer to it when I need to:

https://www.shellac.net/PoundCutChart.html

For whatever reason I've settled on 1.5 pound cut, seems to work for me.

Neal
DRBWWing | Sep 17, 2020 01:08pm | #4
Shellac is probably the most forgiving finish there is. You can remove it and start all over.

I've fixed a few shellac messups by simply wiping with DNA, doing a poor variation of a french polish.

Zinsser is a 2lb cut, I usually thin it by 1/4 - 1/3.

I'm reminded to check my Zinsser cans.

Is Seal Coat available in quarts anymore? I had a hard time finding anything other than gallons.
fivebirdscustom | Sep 17, 2020 03:59pm | #5
By thin coats, do you mean you thinned the shellac? Or just tried to wipe it on as thin as you could, but used it full strength from the can?

I find even Zinsser can be applied well by thinning it with denatured alcohol, or a proper alcohol (I can't get DNA in California, so I use 99% isopropyl). I tend to cut it about 1:1 most of the time, but maybe a little lighter on the alcohol, depending on how it feels going on.

I also find if I even think about trying to put Zinsser on full strength it never hardens up the way I'd like.

But, fresh shellac is always better....
geedubbee | Sep 17, 2020 05:27pm | #6
@robscaffe - I don't see anything that you did blatantly wrong.

"I made sure I thoroughly mixed the shellac and everything while applying, sanded down with 320 after the third coat to level out and started again and waited at least a few hours if not longer between really thin coats."

This is pretty much how I lay down shellac. In my area I wait only 30 to 40 minutes to be able to sand. My first reaction was "applied too thick" until I read that you used thin coats. Now I will go with "too old".

I run Zinsser Seal Coat that is 3 years old without issue so I definitely stretch the limits. I get a little cocky because I use a lot of shellac and "we" have an understanding.

Zinsser had stopped using the mystery code for dates shortly before Rustoleum picked them up but, I don't know what it is now. You could check the Rustoleum site.

The good news is that a rag soaked with DNA and some scrubbing will remove most of what you have down. A quick surface prep and application of new product may set you right.
shankahoe | Sep 17, 2020 05:37pm | #7
Thanks a lot everyone! I actually contacted rustoleum about this issue, with no response so far. But I do appreciate all the awesome responses!
geedubbee | Sep 17, 2020 08:26pm | #8
This was current for the date shown:

The first number is the last digit in the year the shellac was packaged. The second number is the month. For October, November and December the first letter is used instead of a number: “O,” “N,” or “D.” The third and forth numbers provide the date within that month. Apr 29, 2016
cowolter | Sep 18, 2020 06:36am | #9
There is a book by a French guy called the furniture bible that you may find interesting. He did talk about over working the shellac, but also you may have sanded the wood at too fine a grit for the shellac have something to bite on.
gulfstar | Sep 18, 2020 08:35am | #10
In his furniture bible book, he starts by stripping the existing finish using denatured alcool with a coarse rag . He then seals the piece using long parallel strokes with a pad charged with shellac waiting an hour to start the polishing process. I sand some of my turnings down to 2000 grit without adhesion problems.
old_wood_guy | Sep 19, 2020 12:23am | #11
It may be that shellac is just simply too soft of finish. If it does not seem like a hard enough finish to resist indentation from the pressure of objects, try adding a harder finish over it. I'm adding coats of varnish over shellac. What's going on about comments relating to shelf life? Could that be an issue with the age of the shellac you're using?