I'm looking for advice on how to repair a split soundboard that I don't think meets the usual criteria for this sort of job.

The instrument in question is my own opus 1 replica of the earliest Trasuntino, which was left overnight at a concert venue which I only too late discovered was horrifically dry (the violinists in the group later told me their instruments always had problems playing at this location).  The instrument was fine one evening, but a large split had developed by the following afternoon, travelling from the upper bellyrail right to the bridge, approximately in line with the F above middle C.

In examining the split, it appears to have happened right at the joint between two pieces of wood, so it's very clean and very straight.  Moreover, the two edges have not pulled apart sideways, but have displaced vertically about 1 mm or so.  I can actually press them back together with the fingers, and the crack disappears completely.  The instrument was completed in 2009 and had never cracked previously.

In line with the conventional wisdom regarding splits, I would not bother fixing this, except that in dry winter weather I am hearing a clear buzz when I play certain note and chord combinations, so something has to be done.  The crack happened in the early months of 2015, and in humid spring/summer weather, the soundboard seems to expand enough that the cracked edges press together firmly, eliminating all buzz, although the vertical displacement of the edges can still be seen.  I'd also have to check to see if the soundboard has lost contact with the underlying rib.

My question is, does such a crack need to be shimmed, since it is exceedingly straight and clean?  Could I rig up some way of pressing the joint together, after introducing glue, or is there no hope of such a repair succeeding in the long run without shimming?

Lastly, since we seem to be on a glue "kick" these days, would a slightly flexible hide glue (i.e. doctored with urea) be better for such a repair, given that the board has already cracked once?

BM

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