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The Shellac hoax

11K views 103 replies 38 participants last post by  ETwoodworks 
Here is the article:
http://www.woodshopnews.com/columns-blogs/finishing/502292-shellac-as-a-sealer-its-all-just-hype

Basically he makes the wrong argument… that shellac is difficult to use. I don't find it difficult to use. In fact I find it easier than poly or varnish and more durable than wiping varnish unless you build up a lot of coats. A sealer coat of shellac sanded smooth is much faster and easier than a sealer coat of varnish and much easier to sand. Plus I like the amber tint.
 
Recently I found a can of Zinsser shellac that's probably several years old. 'It's no good,' I thought. Used it on a footstool project anyway and it's as good as the day I bought… so far, hoping it doesn't wrinkle.
 
Won't use shellac which has been around for centuries because it might crack.
Uses nitrocellulose lacquer instead which is certain to yellow and crack. It's like a terrible meme.
 
Formby's Tung Oil is 70% mineral spirits and an undisclosed amount of tung oil based varnish, according the MSDS. It's not tung oil.
 
The actual product name is Formby's Tung Oil Finish and is does contain Tung Oil.

Claiming it has tung oil in it isn't very useful. It contains a tung oil based alkyd resin. Basically a fat (in this case, tung oil) is added to a polyester resin, magic happens and it becomes a varnish. I'm not an expert on alkyd resins, I don't know if the specific fat has much effect on the final finish but I suspect not. At the end of the day, the tung oil description is a marketing ploy. The important thing is that you don't confuse it with tung oil, it is 70% mineral spirits and ~30 or less % varnish.

When using stain is it not preferable to use a pre-stain wood conditioner under the stain, rather than shellac?

Some woods absorb stain unevenly causing blotching. A conditioner is just a weak finish so that areas of the wood that would absorb the most stain will fill with the conditioner first so the stain goes on more evenly. Shellac works just fine as a conditioner you just need to thin it down with alcohol first. If you don't thin the shellac it will completely seal the wood and won't accept stain.
 
Earlier I asked where this idea came from that shellac was a better barrier and people talked around it but didn't answer directly so I did some research. It appears that shellac is slightly better than some lacquers and polyurethanes at resisting water vapor. The data is hard to read the way it's presented but if I followed it correctly, shellac was better than satin finish products and about the same as glossy. However shellac did degrade slightly faster than some polyurethanes. All in all the differences were so close as to be insignificant. Here is the file if anyone wants to root through it.

http://www.fpl.fs.fed.us/documnts/fplrp/fplrp462.pdf
 
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