I dont think CA would do well for soundboard cracks. Maybe if they were really thin hairlines... but I doubt it. You can use an epoxy. I have used West System epoxy in the past with great success for years and never had a sign of a soundboard re-cracking along the old crack lines. You tape the underside of the cracks so the epoxy doesnt just leak through. Use some good strong adhesive tape. The epoxy does not need to behave like wood in the face of humidity changes. It just needs to hold on to the edges during tension periods and stand up under the pressure during compression periods. The rest of the wood (probably 99.% percent of the total resultant panel) will take care of dealing with humidity changes. By the sound of your question I'd like to add that this kind of job is done with the strings removed.... just in case there was any question. If the pianos sound good, and the cracks are only thin more or less hairline in character... I wouldnt bother. In fact I dont bother with filling cracks in soundboards anymore as a general rule. Cheers RicB This question was posed to me yesterday by the facility manager of a local community center: could a cracked soundboard be repaired by dripping CA into the crack (as is done with bridges)? My questions were: would CA hold up and would it help? I didn't know the answers to any of those, although I could hypothesize some. BTW, I told him NOT to try it, since both the pianos with cracked soundboards are Steinways: a 1950s B and a 1931 L that's been rebuilt and refinished. And nobody ever mentioned (or remembered) to think about humidity control. Harrumph! The cracks aren't horrid, but they are there. Thanks for any comments. Annie G. * Previous message: Soundboard stiffness variances
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