This image shows the soundboard being repaired with shims. This is performed in our "hot room" with as much humidity squeezed out of the soundboard as possible under intense heat, then the shims and glue are added for the repair. Once the repair is made, the shims are trimmed, the soundboard sanded, and then refinished with appropriate sealing/finish material. The metal plate has to be removed from the instrument for the process.
This is similar to open heart surgery on a piano, for the soundboard is the "heart and soul" of the instrument (...as I have been told my several retail piano store sales folks). This same type of repair can be performed on some grand case restorations, if the soundboard has good curvature and the repairs not too extensive. However, for the majority or of our grand case restorations, the soundboard is replaced.