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Has anyone ever had this happen?
I have a can of "Denatured Alcohol." I bought it at Wal-Mart (my first mistake). The brand is Crown, PSC, Packaging Services Co., Inc, Pearland, Texas, 77581, www.packserv.com.
I'm refinishing some guitars. Initially, I used Qualasole, a padding lacquer, I know to contain nitrocellulose lacquer and a number of solvents and lubricants in a proprietary formula. I had partially finished one instrument and had an "accident." I was using a non-woven pad, which is actually a paper product. The Qualasole film was still soft, I absent-mindedly hesitated in my padding motion, the pad "caught" in the lacquer film and a hunk of paper fibers ripped right out of the pad and embedded themselves deeply in the film.
In my heart I knew I would have to take the lacquer down almost to bare wood to get the mess out, but I tried to "finesse" it and "pull" the fibers out with gentle steel wooling. It worked to an extent. I decided to try wiping with alcohol to "wet" the fibers, thinking they might further let go.
I have used alcohol many times on guitars to clean off embeded skin oils, without any damage to the finish, ever.
I have used Qualasole routinely for over 20 years, and pretty much know its characteristics, but I'm not sure if I ever actually applied alcohol over it. Any surface I apply Qualasole to is then pretty much a "virgin" lacquer surface, not needing any cleaning from that point.
I wiped an alcohol-damp pad over the Qualasole film and was horrified to feel and see the alcohol take the finish off like I was using lacquer thinner! Luckily I didn't destroy too wide an area. I let it dry, carefully sanded with 400 grit, then steel wooled it, and gradually repaired the area. All the while, puzzled that alcohol could do that to Qualasole. I figured it must contain shellac in addition to lacquer, and that's why it wiped off like that.
Then I had to make much more extensive finish repairs to several other instruments, requiring full-blown lacquer spraying. The work required me to mask off large areas with low-tack masking tape as I went. After I removed the tape from the top of one guitar, I saw some gummy adhesive from the tape.
I reached for the same alcohol to remove it. I don't know why I reached for alcohol. I have removed adhesive from lacquer surfaces a million times before with mineral spirits. Mineral spirits is absolutely, perfectly safe on lacquer finishes.
I wiped the alcohol on the guitar, and, you guesed it - the finish came right off!
This was pure, dry, nitrocellulose lacquer. No shellac on that guitar whatsoever. That instrument had 3 days worth of my meticulous spray finish on it.
I found the MSDS on the Internet for this brew of devil's denatured alcohol. Here's the part describing the contents:
CONTAINS: 65-75% METHANOL (67-56-1)[200-659-6],
20-30% ETHANOL (64-17-5)[200-578-6],
< 10% ISOPROPANOL (67-63-0)[200-661-7],
< 10% METHYL ISOBUTYL KETONE (108-10-1)[203-550-1]
Look at that last ingredient. Methyl isobutyl ketone! LACQUER SOLVENT! Very potent stuff.
What in heaven's name is THAT doing in there? Is this a denaturing agent?! The stuff is already 75% methanol. What further denaturing is needed?
I guess we have to read MSDS information now before using solvents for finishing, and be chemists, as well.
The can lists "cooking fuel" as one of its uses! With methyl isobutyl ketone?! I know how to handle an alcohol flame. But alcohol and ketones are the stuff of Meth labs and violent explosions.