Ive seen soundboards that cracked again right alongside a shim. Is shimming a good repair?
Any soundboard can fail if subjected to enough climate stress. However, shim failures are usually due to improper methods. Hand shimming repairs (carving out the crack with a V shaped tool) are subject to failure for several reasons: Such tools actually crush the wood along the sides of the crack, leaving damaged wood at the glue joint. They also do not remove wood adjacent to the crack that has been damaged by the stress that created the crack in the first place. Due to grain irregularities, hand shimming seldom results in a perfectly uniform groove, so you don’t get the thin, void free glue line necessary for a high strength joint. Other reasons for failure are the use of epoxy (rather than a water soluble glue, so the glue line fails to expand and contract with the surrounding wood) and improper drying of the soundboard and shim wood prior to repairing. Finally, boards can fail again if the piano is subjected to the same climate stress that damaged it in the first place. A properly
