Less Durable Over More durable ?? Makes no Sense to Me !

[yankees1]

Having a new mandolin built and the builder will be applying a spar varnish on it which is very durable. Why would I have a french polish process applied next when FP is less durable than the spar varnish ? It just doesn't make sense to me to apply a less durable process over a more durable product ! I have one week to decide but at this point I am skipping the FP !

[multidon]

One way to think of the French polish coat is as a sacrificial coat. If it gets scratched or damaged it can be repaired easily. Some even get a renewal coat every couple of years or do. Look brand new again. On the other hand if you go with just varnish and it gets damaged it is much more difficult to repair.

[Dale Ludewig]

By FP, I'm assuming you mean shellac. I've done just what you're referring to. It's always puzzled me a little also but I believe the reasoning goes thusly: You get a fast build with the spar varnish, and if it's the spar varnish I'm thinking of, it dries hard, unlike some spar varnishes. Then the FP process goes on over the varnish and the process is much faster than building up with FP from scratch. And you get the FP look, which is a softer glow than just the varnish. It's only a coincidence that the undercoat is harder than the shellac.

[sunburst]

The original idea was to speed things up, or at least that's what my research (such as it is) leads me to believe. Oil varnishes are slow to cure compared to more recently developed finishes, and it takes a while for them to cure enough to buff to a high gloss. Even when they are cured enough to buff, they often display witness lines (lines that show where one coat buffs through into the underlying coat). A FP treatment over the varnish avoids witness lines and speeds up the process by giving the finish a gloss earlier than it possible with oil varnish alone.
Gibson used oil varnish on the early '20s F5 mandolins, and being a production shop, they needed those things done and sold as quickly as possible, so by applying spirit varnish over the oil varnish they could move mandolins through faster. In 1925, the much faster nitrocellulose lacquer became available, and since that process was so much faster, Gibson immediately switched to nitro. That change coincided with the departure of Lloyd Loar, and later, when the Loar signed F5s became the "holy grail" of mandolins, people started "nit picking" the differences between them and the later Gibson mandolins, and the finish was an obvious difference. Since the Loars are considered superior to all others, and since they were varnished with the muliti-step system, people concluded that sealer, oil varnish, shellac based top coat is the best mandolin finish. "Good enough for Lloyd load, good enough for me!".
So that, in a nut shell, is why people put a less durable finish over a more durable finish.

[Jim Hilburn]

The only thing I might add is that to do a fp "spit shine" over oil is much different than trying to build a complete finish with shellac so your kind of getting the best of both worlds.

[yankees1]

There must be different products/procedures for a FP final coat so I assume the success rests with the individual builder. My concern is that I have had FPolished instruments before and had extreme problems with cloudiness appearing in the finish and very easily marked. Even with no contact on the back or front with my skin this cloudiness appeared and I'm too picky to go through these problems again. So, I will leave it to Mr. Heiden to determine which way to proceed !