Stable Cracks

I have seen the phrase "stable crack" used fairly often, often in "for sale" ads. But I confess that when I think about the phrase I have difficulty understanding just exactly what it means.

How long do I have to watch that crack before I can call it a "stable crack"?

Does a stable crack affect the musicality of the instrument? If so, in what way?

Does a stable crack reduce the structural integrity of an instrument?

Does a new crack become stable if it is glued or cleated?

Other than waiting and watching the requisite amount of time to see if the crack grows, is there some other way to determine if a crack is stable?

I would define a stable crack as one you can see but is not causing any immediate structural issues with the instrument. In other words, if the crack makes the instrument unplayable, then it certainly is not stable and needs to be addressed. If not, it is a gamble, IMHO.

My own experience 40 years ago I owned a 1951 Gibson L4-C guitar that the top had developed a crack, more accurately a seam separation, that extended from the tailpiece to nearly the bridge. The guitar was this way when I got it, it played and sounded fine, I always planned on getting it repaired, but never got around to it. I owned the guitar for many years and the crack never seemed to go anywhere. I sold/traded the guitar in this same condition, FWIW.

Cracks appear for a number of reasons. I have glued cracks that have been stable for 30 years. I guess you could call that a stable crack. Tops and backs are joined without cleats and are fine, you could consider them stable cracks. A crack glued properly that is not under stress, push hard to join the crack, should be fine all things considered. If excessive dryness or moisture are a factor anything goes.

It's a good idea to check repaired cracks every now and then.
Depending on the size and location of an active crack, its effect on the structural integrity of the instrument may be very small, or it may be critical.
For someone without a strong repair background, it is usually safe to run a drop or two of water over a crack, push on the surrounding area very gently, and see if the water shows any signs of sinking into the crack.


A crack that has not been attended to will often spread, and may have an adverse effect on the tone of the instrument. I call that unstable.

I call one that has been correctly repaired and has not come loose again "stable." If the work has been done conscientiously, its effect on the "musicality" of an instrument should be neglibible.

My experience has been that well-repaired cracks do not often open back up.
One that has been poorly repaired and has loose spots is unstable.

A crack that has had a huge cleat installed [and I've seen some really big ones] might be stable, but if a cleat is too large, it will not help the sound of the instrument.

I sometimes use cleats, but I keep them small.

In the case of Bill Monroe's crashed and repaired F-5, I don't know whether or not 20+ years after the restoration that the instrument is still stable or not. I'm sure that Charlie D. did his absolute best. Since that instrument resides in a museum and is not often played, it seems to me that it doesn't matter very much.

I define a stable crack is one that hasn't moved since the initial crack or been glued, cleated & hasn't progressed any further. In either case, you're trusting the seller to be honest so I tend to proceed very cautiously or not at all. If you do trust the seller, a truly stable crack will only affect resale value. Even the most shallow finish crack is still a weak point & should be monitored closely. I have a Taylor 812 that arrived with a very small finish crack in the back about 3 years ago. It ended up almost closing after a week and it hasn't moved since. My humidty is stable so, though I check it regularly, I don't worry about it.

I've had several experiences with cracks, both large and small.. I repaired a violin a few years age that was run over and deemed "unrepairable".. They said they wanted it put back as best as possible, if nothing more then a wall hanger.. After seven cracks were cleated and leveled, it was a total success.. Said that it sounded as good or better then the original violin.. It was made in 1785.. Quite proud thinking I continued the joy over the last 250 years.. . I'm now working on a Martin 00-17 made in 1947.. Replacing the whole top. but again, there were many cracks on in the back and sides to be cleated.. Hoping that the cleats hold as well as with the Violin.....

I would say there's no such thing: stable repaired cracks yes, not stable cracks.

If I'm the advertiser, then I call old historical repairs that clearly haven't moved in 50 years stable, and anything that I've done as simply "repairs".