shellac woes

It turns out the Zinsser clear shellac I was trying to use up was made in 2016. The first coat dried to a hard shell in about 30 minutes, after one hour sanded at 320 grit just fine, and the second thin coat took about three days to fully cure.

I found this article at pop woodworking: https://www.popularwoodworking.com/f...s-eye-shellac/

and found a new quart can of clear zinsser at team blue this afternoon that was made on April 22, 2022 unless they have changed the date codes around.

I am planning to bring in shellac buttons and denatured alcohol for future projects, but I really need a finishing/ chemicals cabinet first as I am kinda overdrawn in the shelf space department currently.

If I can put fresh/new shellac on top of out of date slow curing shellac, how long should I wait before I start putting the new stuff on?

The veneer surface I am trying to finish is only about 1/32 thick, I really really do not want to sand back to bare wood unless there is simply no other way.

I am kinda leaning towards doing an exceedingly thin layer of the new stuff so once that is cured the new surface will be 50-50 old/new, and etcetera.

Thanks

"Old stock" can do that sometimes, even though Zinsser products do seem to have a reasonable shelf life. 'Hope the uber-thin coating resolved things for you!

Yep. This wasn't an envelope I pushed intentionally, but there are some folks around who use more shellac than me.

My current plan is to let the old shellac that is already on the project continue to cure until Saturday afternoon, double check here for experienced replies, and then probably use the rattle can product to get a really thin coat on and give that a full day, maybe spray again Sunday afternoon.

It will be what it will be.

So far so good. I have no idea what my longevity is going to be.

Short version I put coats of aged shellac on a birch veneered plywood. The first coat dried in about 30 minutes, the second coats required days to dry. I learned to read the date code on the Zinsser premixed shellac from the home store.

With fresh shellac on hand, I waited 48 hours after the first two coats of old shellac were cured, sanded very lightly, successfully, waited 48 more hours. This afternoon I was able to apply 3 very thin coats of new spray can shellac, waiting an hour between coats. I had two problem areas representing about 1% of the total area to finish that only got two coats today. The other 99% is dry to the touch in less than 15 minutes.

My plan from here is to wait another 48 hours, and then maybe another three thin coats from the spray can Monday evening, and then see if I can finish sand up around 400-800-1000 grit Wednesday evening. If all that goes well I will see about actual finish coats on Friday evening.

I am still afraid this is not going to "do right" long term; but I won't know until long term gets here.

If you are reading this thread as a search result in 2025 or something feel free to send me a message as the project will very likely still be in service.

Just don't overdo the number of coats f shellac you plan to end up with. Shellac doesn't need or even like, too many coats.