Official Luthiers Forum!

Here's one that's new to me.

I have had two instruments (in the last 6 months) that began to get lacquer checks immediately after being finished and sanded, but prior to buff out. I actually sat there and saw two checks develop before my eyes. Talk about upsetting!<G>
This is occurring only on the tops...from the purfling into the face of the top and likewise from the rosette. I have gone back through my build notes and the only things I find in common on the two builds is 1) the use of fish glue on the purfling and rosette inlays and 2) Mc Fadden lacquer from the time shortly before their demise.
Shop conditions have remained stable...temp between 60-70 degrees and humidity at 45%, give or take a point or two.

My guess is it is something to do with the fish glue as there are no checks elsewhere on the bodies but I have heard less than great things about McFadden lacquer from that time frame, too.

So, the question to the forum...have any of you had any similar experiences.

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Hank Mauel

I've been using fish glue on binding for over a year with no problems (not rosettes). If it is the glue on the binding then why would it not also happen on the back and possibly the sides? Did you complete other guitars during this time using the same glue and lac? I use Mowhawk Nitro.

Josh

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Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

These particular guitars had "tortoisoid" binding. I used the fish glue only for the purfling on the top (and rosette inlay) and then used the Weldon adhesive for the bindings...hence no checking elsewhere.
These guitars were consecutive finishes with the McFadden.
I am going to the Cardinal lacquer now. Most recent guitar has had the top finish stripped to bare wood so it will get the new lacquer....crossing my fingers!<g>

I must admit this is a very strange situation. It tends to dicount the actual lacquer since no checks occur elsewhere. But why would fish glue cause a problem. It benign organic stuff. This really has me stumped.

By the way, the purfling is a cherry/ebony/cherry layup from Gurian that I have used for years without incident.


Hank (still scratching head)

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Hank Mauel

Hank, I've used fish glue for rosette and binding/purfling on more than 30 instruments now and not seen any effect. I can't see how the fish glue could cause this, assuming that it had been left long enough to be thoroughly dry and hard, so no shrinking.

Colin

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I don't believe in anything, I simply make use of a set of reasonable working hypotheses.

Yes, the bodies sat for a month in the white before I even sealed them with a light coat of shellac. Same procedure I've used since last century and never anything like this.
Makes an old guy say .

Hank

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Hank Mauel

Hank, Do you always use tortoisoid binding, or similar binding? I always use wood binding with fish glue. Just wondering if it could be some kind of movement in the wood and the binding not moving at the same rate (this seems unlikely since from what you said the guitar have been kept in a controlled environment).

Josh

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Josh House

Canadian Luthier Supply
http://www.canadianluthiersupply.com
https://www.facebook.com/canadianluthiersupply?ref=hl
House Guitars - Custom Built Acoustic Instruments.
http://www.houseguitars.com

I bought a gallon of McFaddens from Grizzly when I heard they were finally closing up. I have not used any of it yet, and I probably won't use it at this point due to the potential problems. It would not surprise me to hear that they scrimped on the ingredients on that last batch.

No, these tortoisoid bindings were by request... normally I use wood. The purfling was first glued to it's ledge with the fish glue, then the bindings glued with Weldon ... which I have used before without incident...several days later.
To confuse the issue, both rosettes were abalone which is my standard and each developed checks radiating out from the ab ring. And the rosettes had been install for several months before any finish.
Only other common factor was both tops were Adi, but it was ancient stuff, having been in my shop since last century and well cured. In fact, all the component wood parts in these instruments came from supplies at least 5 years in my shop.

But, now that the top is stripped, I think I will very carefully paint a thin layer of CA around the binding/purfling and let it wick into, and hopefully consolidate, the joints. Time for my spray mask as CA and I don't play well together!

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Hank Mauel

I still have several gallons that will become "fossilized" before they are ever used!

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Hank Mauel

I know many will scoff when I say this but I would bet it is the shellac . The government will dictate what manufactures may and may not use. A few years ago they had to stop using certain volatiles . These helped the lacquer melt in but it won't work like it used to. I had this problem about 10 yrs ago and stopped using shellac as a sealer and the problem went away.
Use the manufactures recommended sealer as it will be chemically compatible to the finish. I use fish glue and don't have any problems . Also are you using any thinners or retarders? The chemistry of changed over what it used to be.

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Thanks, John...
Hmmmm...very interesting. So it's not really my home brew shellac, it's the fact that the "new age lacquer" won't grip to it like the good old days. I did notice that when stripping the top lacquer (with Jasco) that it was a very gummy, rubbery mess...not at all like Jacso takes off "old" finishes. I have stripped much older guitar finishes and Jasco just lifts it off in "sheets", smooth and clean. Not this time.

Well, it is a possibility...the incompatability of shellac and current formulated lacquers. I was planning to just shoot straight lacquer to refinish the top..just build and sand and build and sand. Any opinion on the use of a thin CA coat over the purfling/binding area?

Also, any thought as to why there are no checks elsewhere on the body...also sealed with shellac?
Body wood is mahogany in both cases.

No on the thinner/retarders in the lacquer.

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Hank Mauel

Hank, you probably got the checking around the plastic binding on the top and the shell rosette because these materials have a larger disparity in thermal expansion rates than the other parts of the guitar which are all wood. I would imagine that if you had left the finish on that eventually you would get cracks forming in other areas. Brittle lacquer is as brittle lacquer does.

Yes, but...
I have used Abalone rosettes, as well as ab purflings, since "last century" with no ill affects. Also have used the various "oid" type bindings over the years without this issue. And since this lacquer came off like a gummy elastic caulk, I'm thinking that John's thoughts on the shellac sealer and the more recent lacquer formulations may have some validity...not to mention what McFadden may have done to their formulation in their waning days.
Will probably never truly identify the actual cause, but a few changes in finishing procedure will be adopted.

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Hank Mauel

Hank, what I meant was that if the lacquer was not formulated with the correct amount of plasitizer and it had a tendency to crack, that the cracks would first show up at the rosette and between the top and the plastic binding because these are areas where there is more differential movement.