Reading Patch's thread about split top on his 'Book' Elite reminded me that I've been wanting to pass along this info about what I think is the root cause of the splits in the tops that happens all too often on our Os. Even my 'Book' Elite is starting to get finish cracks in the lower bout.

When Paul Moody had me re-top his 1113, it arrived with three splits that ran the length of the top from the upper bout to the lower bout, one each on either side of the bridge and a third that went right down the middle. Here's a pic of what the top looked like before I pulled it off the guitar.

In the process of pulling the top off the guitar, all fourn transvers braces pulled off the top. Since I wasn't going to be using the top, I just left them off. I went on with re-topping the guitar and didn't give it another thought, until recently.

Then, when pulling the tops off of the four guitars I'm working on now, I noticed something unusual. All the tops were cupped, to a lessor degree than Paul's 1113 top, but they all were cupped. Here's the 1113 top. This photo shows the cracks a little better. This top is the worst because it has no braces across the grain to hold the top flat.

And, the 1528 top.

The 1612 top.

Lastly, Paul's 1117 top.

So, I got to thinking about would cause all these tops to warp. All were different types of wood and different ages. Paul's 1117 was the newest, being rebuilt at the factory. The only common denominator was the finish -- poylester resin.

When molding fiberglass parts, one of the benefits of using epoxy over polyester is what's known as dimensional stability. In common terms, polyester resin shrinks. Not much, but it's enough that most quality parts are molded from epoxy. There are other reasons for using epoxy over polyester, but one of the big ones is shrinkage.

Stabilizers can be added to polyester resin to help minimize it, but it will still shrink. If polyester resin were used on one side of thin wood, like our guitar tops, and it were to shrink, it would warp the wood unevenly. Since the tops are firmly glued to the edges of the bowl, any shrinkage would eventually cause the finish, and even the wood, itself, to split.

So, the conclusion I've come to is that the finish cracks we so often see in our Os is caused by the shrinking polyester finish.

What can we do about it? Short of the factory using a different finishing system, Not much. I just thought I'd pass along this info to remove the mystery of why our guitars' finish cracks.

As you can see, the top has three main waves, each separated by the cracks. What it looks like to me is happening is that the polyester continues to shrink, but the wood doesn't. As it shrinks, the wood deflects inward. At some point, when the wood can deflect no more, either the finish will split or the wood will, usually in spots where there is no bracing on the underside to support it.

Taylor Factory Tour Part 3 of 4 - Finish Application

Taylor Innovation: Electrostatic Finish Spraying and UV-Curing

To get the tops off, first I pull the binding. Depending on the top, sometimes I also pull the purfling to expose the glue joint between the top and lining.

Next, I use an Xacto chisel to separate the top from the lining. This part takes a little while to do, maybe 20-30 minutes.

This makes a lot of sense. Those three main waves are evident on my 1717 as well. I can feel each wave when running my hand over the soundboard. *sadface*