Does shellac really go bad?

[Steve Soldo]

Does shellac really go bad?

Honestly I don’t use shellac as a primary finish at all. However, I use the Seal Coat product all the time as a sealer prior to spraying water based polyurethane. I often add a drop of Transtint dye to bring the figure out of wood, especially maple.

But this stuff has become more expensive. About $15 a quart. However, you can get a gallon for about $35. I read all the time that shellac has a limited shelflife. But I have used Seal Coat that is over a year old, for this purpose, and seems to work fine.

Question: When using Seal Coat shellac for this purpose, would it go bad if kept, let’s say, a year or so?

[fredhargis]

Yep, it goes bad. Fresh mixed flakes can last as little as 6 months, though I've seen some that was usable after one year. But Zinnser has some magic that slows down what the chemical reaction is in the mix, and it seems like I've read that their stuff lasts as long as 3 years. The problem i have is that I never know how long it's been in the store...and they changed the code date system to one I can't interpret. So the best thing to do (in all cases) is to test any that has aged before using to see if it's still good. Don't forget, the Zinnser stuff has a bad habit of developing a leak in the can...so keep it in a plastic bag when stored for long periods.

[Cooler]

I use Sealcoat until the container is empty.  I've never had issues with old Sealcoat.

[Roly]

Paint some old shellac on glass and see if it dries. If it stays sticky throw it away. Roly

[Strokes77]

It definitely gets old and goes bad. And yep the issues I've had is it won't dry it gums up

[chapeleastland]

Denatured alcohol attracts water from the air. Water doesn't mix with shellac. Once opened to the air, water is soon to follow.

I like shellac for many reasons and most every project gets a 1 lb cut coat at least once.  I only use flakes, make up what I need for each project, then toss what's left over. I have very little waste.

Mixing shellac is not a problem. For a 1lb cut I use a pint mason jar, one ounce of flakes to 8 oz alcohol. Cap it, and use a magnetic stirrer to dissolve in a few hours or overnight.

I can apply several coats quickly as the first coat is dry almost immediately as it's applied.

There's really no downside to shellac if your understand it, but it's not promoted by many finishing manufacturers as it's so easy to make in the shop at very low cost.

[EricU]

I have never had any of the Zinsser shellacs go bad on me.  I recently used up a fairly old can of the amber, and the seal coat I have still seems to dry pretty well.  I usually cut it, don't know if that changes the life at all though.  

What I have had happen, and is apparently fairly common, is the shellac eats through the can and ends up on the floor.  At first I blamed myself and then I happened to see something about it (here maybe?).  I'm pretty sure that a gallon would last me long enough that it would empty itself onto the floor.

I keep intending to go with flakes, but it takes effort to get good alcohol and I'm lazy.

[Bill Lyman]

Does shellac really go bad?

Honestly I don’t use shellac as a primary finish at all.  However, I use the Seal Coat product all the time as a sealer prior to spraying water based polyurethane. I often add a drop of Transtint dye to bring the figure out of wood, especially maple.

But this stuff has become more expensive. About $15 a quart. However, you can get a gallon for about $35. I read all the time that shellac has a limited shelflife. But I have used Seal Coat that is over a year old, for this purpose, and seems to work fine.

Question: When using Seal Coat shellac for this purpose, would it go bad if kept, let’s say, a year or so?

One book on finishing says you can keep flakes indefinitely, another said flakes go bad after a year. I have used flakes that I keep sealed in the refrigerator over 4  years and they were fine.

[Admiral]

One book on finishing says you can keep flakes indefinitely, another said flakes go bad after a year. I have used flakes that I keep sealed in the refrigerator over 4  years and they were fine.

I have flakes that are 15 years old and still are just fine.  I did, however, keep them in double (triple) plastic zip bags (i.e., each color as packaged in plastic from the vendor in its own zip bag, then all together in a gallon zip bag) in my basement fridge.  I can't imagine not rolling my own, and use it for almost every project in some shape or manner.

[hbmcc]

I can never remember which Zinsser product has wax. Yes, the cans magically began leaking and refusing to dry. 

I went to flakes and makeup only what I expect to need. At first, I played with all the types offered but soon settled on the three main tints of non-wax flakes. The buttons and older versions are really for antique and period finishing. They look and layout pretty crappy on modern furniture. Home mixed shellac should never be saved beyond a project's needs. This has appeal for mixing tints into the blend. 

The big issue for me is alcohol storage. I hate buying little cans every time I mix up but gallons tend to go too wet (water) quickly.  Stay away from cosmetic/isopropyl products. Because the alcohol ages so quickly, and it dries so fast, I am free with the cuts after initial solution, and rinse liberally if I like the container.