Lacquer lifting

[graham darden]

Good morning,
I am having problems with the lacquer, applied over two coats of shellac, lifting in the inside corners. Like where the neck meets the rib and where the fingerboard extender meets the top. Lifts up and creates a bubble. Do not know if I may be spraying the lacquer to thick in these areas or what. Any suggestions will be appreciated.
Thanks, Graham

[sunburst]

Dewaxed shellac or not? What lacquer? How was the shellac applied how was the lacquer applied? How long between the shellac and the lacquer? Was anything done to the shellac to prepare for the lacquer?

[graham darden]

Thank you John,
Dewaxed shellac mixed fresh. Behlen stringed instrument gloss lacquer. Shellac and lacquer were both applied by spray. First coat of shellac cured 2-3 days. Second coat was applied 45 minutes before the first coat of lacquer. Nothing was done to the second coat of shellac prior to the lacquer.
Graham
PS. I still want your bandsaw. Haha.

[graham darden]

Lacquer was cut 1/3 thinner to 2/3 lacquer using Sherwin Williams R7K120 thinner. Fairly hot but not the hottest.

[sunburst]

I thought I posted a response earlier but I must have neglected to click "Post".
I don't really know what the problem is, but I have always let my shellac sealer dry and then very lightly sanded before applying lacquer. Maybe your the lacquer went on too soon.

[rcc56]

I am no expert at finish work, but I am learning that, for me at least, the two biggest causes of finish problems are insufficient drying time and laying finish on too thick.

[Jim Hilburn]

I've been pretty dormant for a while but I'm doing a lacquer finish right now. I've been told that shellac has a shelf life, even the flakes, and I was worried about the age of mine. So I bought a can of Zinnser Seal Coat dewaxed which is available locally instead of buying more flakes. Went on nicely and no problems so far.

[sunburst]

...I've been told that shellac has a shelf life, even the flakes...

I've been told the opposite; that flakes, kept dry under good storage conditions, have a nearly unlimited shelf life, but when they get really old they can become harder to dissolve.
I wonder which is correct...

[rcc56]

They do get old and hard to dissolve. When I have used shellac that old, I had drying problems.
I've had drying problems with old oil varnish also.
Now I date most of my finishing supplies and glue when I buy it. I discard them after 12 to 18 months.
Hide glue granules are an exception, they'll last for years. Duco cement seems to last a long time also.
Does anyone know if sandarac has a shelf life?

[Jim Hilburn]

Well it was a guy with the initials SG that told me that.

[sunburst]

...Does anyone know if sandarac has a shelf life?

Since I don't know, I treat sandarac like I do shellac; dissolve a small amount at a time and keep the flakes (or "globules" in the case of sandarac) in an air tight container assuming a much longer shelf life for the undissolved resin.

[amowry]

I had a similar problem (pulling away from inside corners) with Cardinal lacquer over shellac, and I've since talked to several other builders who have seen the same thing. I switched a to light coat of vinyl sealer, and that fixed it. By the way, the look of the sealer is totally indistinguishable from shellac sealer, contrary to what I had always been told.

[Dale Ludewig]

I've not used Cardinal lacquer. Mostly McFadden's or Mohawk nitro. Like Andrew, I use a vinyl sealer before the nitro. I have used a little shellac in the dye if I want a toner effect. But always the vinyl before the lacquer. Never had any lifting issues.

[graham darden]

I shot a lot of lacquer back in the day on furniture. Always used Sherwin Williams sealers and lacquers. Did shoot 2 guitars back then with their guitar lacquer and sealer. No problems. Need to look and see if they still have that product out there.
Thanks to everyone. Graham

[graham darden]

Needless to say, fixing these areas is a genuine problem.

[Dale Ludewig]

Graham, can you post pictures? I'm wondering if you could hit those areas with some compressed air to blast the loose stuff off and then spray just some solvent on to kind of melt things together. Just a thought.

[graham darden]

Thanks Dale. I have already started the repair process, so a picture would not be good. I am doing close to what you suggested. Putting solvent on the bad and trying to push it back down. The finish on your stuff is awesome.
Graham

[Jim Hilburn]

Did some research on a woodworkers forum and there was talk of making sure your alcohol is fresh. It takes on moisture after being opened.

[graham darden]

Dale,
If I am successful at getting this settled back down what do you think of dusting in some light coats with an airbrush to get everything slick again?
Graham

[Dale Ludewig]

Graham, if you think you've got stuff settled back together, the "dusting" is an idea. I'm not sure what you mean by slick. Sooner or later (probably sooner) you're going to have to get a wet coat on there. If for some reason there's contamination involved, that's when it will show up. The dusting is just putting little molecules of the finish on there but not wet enough to flow together. Or not, which will be the tell tale sign. I don't understand why the adhesion problems are only in those areas, the corners. It seems like there must be something special going on there. Some residue from a previous operation that didn't get washed or blown away.
I think I'd get it where it looks settled back down and then spray a coat or two of sealer (I'd use vinyl). Then make sure it's dry (like several hours) and then rub it with something like an old t shirt material. That should allow you to figure out if the stuff is adhering to each other without going into the color.

[sunburst]

Now we're into something I remember from chemistry class.
Ethanol and water form an azeotrope. That means that roughly 90% (10% water) alcohol is stable. I use "Golden Grain" alcohol from the liquor store for mixing shellac. It's what is commonly known as "pure grain", and it will remain 180 proof (90%) and not take on water.
Those of use lucky enough to be able to get absolute alcohol have a product that will absorb water from the air and revert to 90%.
90% is the best we can do through distillation because an azeotropic mixture has a lower boiling point than either of the two components alone.
So anyway, "pure grain" does not take on moisture and can be successfully stored. I don't know of anywhere in the US where one can legally get absolute (100%) alcohol without a special permit, though it is available in some other countries. There was a 55 gallon drum of the stuff in the store room of my organic chemistry lab in college. It had to have special double seals to keep it from taking on moisture (and every ml used had to be accounted for).

[Dale Ludewig]

I can testify that Mr. Hamlett has shown me some of the absolute alcohol and the last thing I had on my mind was finishing a mandolin or guitar.

[graham darden]

You guys are WRONG. Southern term. Everclear 190 has been with me since college. Remember PJ? Thanks for the tip, I have more of it than I do solvent.
Graham

[Dale Ludewig]

No need to get snippy.

[graham darden]

Well I just tried to send pics of repair process but was hindered by user error.