Finish Cracks

[M. Stephenson]

Two of three of my Sevillano guitars are starting to develop cracks in the finish. I try to keep a fairly constant humidity, between 50% and 60%. The guitars are between 5 and 8 months old.

So far the cracks are all on the guitar tops. They are not cracks in the wood, they are cracks in the finish and the cracks do not follow the grain.

My instructors first Sevillano developed finish cracks as well. His others ones were purchased about the same time as mine, so they may develop them yet.

I take it this has to do with the quality and/or application of the finish material.

It bothers me a little, but not that much. I feel certain that the problem will probably get worse.

I am mostly curious as to why this is happening.

[jeremy]

Finish cracks can be caused by many different things, the determing factors are usually the type of finish, the thickness of the finish, whether there are multiple different finishes on the instrument (eg sealer and topcoat) etc.

If the finish is too thick it will eventually crack because it cannot expand and contract as much as the wood underneath it. This is especially so if hard finished like urethanes etc are used.

If there are different finishes on the wood, say if one is a top coat and the other is a filler or sealer, that can cause cracking (usually in the form of crazing). This is because the two finishes expand and contract at different rates as the wood moves with temp and humidity changes.

Sometimes the wood itself may have resins or chemicals in it that react with the finish itself.

Mostly these longitudinal cracks are caused by a finish that is too thick. If it bothers you take the guitar back if it is fairly new. If the cracking gets bad, it can start to curl at the edges of the cracks.
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[M. Stephenson]

Thanks. I will see if I can get some information about the finish thru my instructor, who talks frquently with Sevillano.

The cracks can not be felt with the fingernail and they look like they are under the surface, so it might be a top coat/sealer coat issue.