Hi guys,
A couple of years ago I re-topped and restored a Gibson CF 100. The top I used was purchased from Herb David (original owner of Ann Arbor Guitars) It is German Spruce and was cut back in the 60s and I purchased 6 sets.

When I was choosing the wood from this stash I noticed they were quite floppy side to side but were very stiff with the grain but I was pretty committed to using it since it was almost as old as the guitar.
It went together well and when finished the guitar has a great sound. For the last couple of years I have been "sort of" abusing it and getting it to look "vintage", i.e. scratches, nicks, dings and dulling.

I noticed a couple of weeks ago that the top has started cracking below the bridge. They are not open cracks but more like splits in the grain. I am not bothered by them since I want the guitar to look 70+ years old.

Some things to note:
I keep my house humidity controlled and don't let it get under 40 or over 60, I own 17 guitars about half are acoustics so I keep humidity in check. This is the only guitar I have that has cracked and am wondering if this has to do with the floppy side to side top.

I am reluctant to use the other 5 tops if they are going to crack easily and would like to know what you think about side to side flex in tops.

Thanks for your help on this,

Cheers,
Bob

IMHO, the low cross-grain stiffness and the cracks are unrelated. If anything, more cross-grain flexibility should reduce the chance of cracking.
Is the wood off-quarter? It only takes a degree or two off vertical to significanly affect cross-grain stiffness. That is because the cell structure of spruce is rectangular.

I don't think it has anything to do with top stiffness either. When you retopped it was your shop under good RH control? Did you build an outside mold to keep the shape of the guitar? Could be many things but probably not a well seasoned 60 year old top regardless of how stiff it is across the grain.

Hard to know what's going on without a picture.

Mohawk went through a period of string instrument lacquer being very chippy and check prone. It happened around the time Seagrave went out of business.

I agree with others those look like finish cracks. You can test it with a bit of naptha to see if it comes through on the inside. But wow! That looks great. Really does look like a very old top on that guitar.

Cross stiffness in the top doesn't do much to reduce top deflection in the long run,IMO. It does have an effect on the tone, though. Mark Blanchard did some work on that, and basically decided that you should choose tops with high cross stiffness for guitars, such as Jumbos, that are wider relative to their length. 'Floppier' tops work fine on narrow shapes, such as the old Martin 1 parlor guitar.

IMO. It does have an effect on the tone, though.

I'm not sure I would be so quick to put them in the dumpster (unless the dumpster is code for mailing them to me). I get that you have doubts and are reluctant to use these tops, but I'm not sure you can equate what this top did to what the others will do simply because they came from the same place. Do you have reason to believe the other tops are cut from the same bolt as this one? I ask because the cracks may be a previous fault in the wood that no one would have ever been able to know about when selecting the top. It is hard to tell from the pictures but are the cracks both n the same spot of the bookmatch?

Others with way more experience than I have will be along to discuss this but I'd hold off on pitching them until they do.

The small bodied Panormo would probably benefit from less cross-grain stiffnesss. If you string it up with nylons, like the Ambra 800's I have on a Stauffer copy, you have less than 90 pounds on the strings. Far less tension then on your steel string.

Or better yet keep them. I think what John said makes sense, a very stiff across the grain top might even be more prone to crack then a rubbery one.

I've been sort of busy, which is why I didn't address your question earlier.