Shellac over White Oak???

[Canuck]

I opened a 1/2 full can of Zinssers Clear Shellac today and proceeded to lay a coat onto the inside of a couple of drawers with oak plywood bottom's and white oak drawer fronts. Sides and back are poplar.

After about 5 minutes the oak bottom and the back of the white oak drawer front turned a hideous color of gray/blue/black!!:elvis: The poplar remained the yellowish/green that I expected. Fortunately, its just the inside of a drawer, but I was curious as to why this would happen?

Has the can gone bad or gotten contaminated with something?

I opened a new can of the same product and tested it on a sample piece of white oak and all is fine.

Sure glad I wasn't applying it to the outside of the finished piece.

I will be tossing that partial can but was wondering about what sort of shelf life I should expect on premixed BORG shellac? (I believe the suspect can was close to a year old.

Thanks

Wayne

 

[Howard Acheson]

Sounds like the finish was old and the shellac had eaten through the coating put on the inside of shellac cans. This allowed metallic contaminates to leach into the shellac. When metal contaminates get onto oak they react with the tannin in the wood causing dark colored or black stains.

 

[Canuck]

Sounds like the finish was old and the shellac had eaten through the coating put on the inside of shellac cans. This allowed metallic contaminates to leach into the shellac. When metal contaminates get onto oak they react with the tannin in the wood causing dark colored or black stains.

Thanks Howard!!!:icon_thum:icon_thum:icon_thum

As I was applying it to the plywood, it almost looked like the surface had water stains on it until after it dried. (Dark spots and streaking.)

I tested a new can of clear on a scrap piece of oak and all is fine.

Lesson learned and I thank you once more for having you at our disposal for answering our questions!

Wayne

 

[Bill Clemmons]

Wayne, I read somewhere that Zinssers shellac is supposed to have a 3 year shelf life. They were bragging about some process they've developed to extend the life that long. Sounds like your can didn't quite make it. :thumbs_do

Bill

 

[shopsmithtom]

I've used the same product on oak & had no problems, even though it was at least as old as yours, probably older. I've done it many times. I have to believe that the basic product was not the issue, but maybe some type of contamination that doing it.

 

[CarvedTones]

My experience with old canned shellac has been that it's usually the repeated exposure to humidity that does it in. I think Zinnser's 3 year number is just a WAG based on common/likely usage. You also have to be careful with the alcohol you cut it with (assuming you cut it; most of the premix needs cutting for most uses). I am sometimes guilty of using the alcohol like a cleaner with a rag and have gotten a little "backwash" from the rag in a can before. Then later I went to use it to cut shellac and noticed it wasn't clear anymore.

 

[Howard Acheson]

>>>> that Zinssers shellac is supposed to have a 3 year shelf life.

I believe that is for an unopened can. Could be wrong.

As said, alcohol readily absorbs water from water vapor. Every time the can is opened, additional water is absorbed. Best to not keep longer than a year after opening.