When the substrate or framing members that support a tiled installation fail, they need to be replaced. This includes all many of substrates be it mortar, wood, drywall, or steel. This includes any of these items combined also.
Probably the most common substrate failures occur in wet areas. However, it is not uncommon to find substrate failures in other areas including exteriors. This is especially true if the substrate was not prepared properly to receive the tiled surface.
Nevertheless, all of these failures have one thing in common: the tile must be removed, the substrate must be repaired, and the tile must be replaced.
The following photographs were during a shower pan replacement job on a 1950's residence. The idea was to replace just the shower pan and save the beautiful and somewhat historic original tile work.
During the demolition phase of the job, the wall tile was found to be loose and not adhered to the original mortar walls.
The culprit in the shower pan failure and subsequent rotted floor was several mistakes made by the original tile mechanic in building the shower pan. These mistakes are enumerated in the section, Replace a Leaking Shower Pan.
How the shower pans failure contributed to the failure of the walls in this shower is open to interpretation. The bottom line is that the entire shower had to be replaced due to water damage.
The mortar bed failure was evident by the excess both horizontally and vertically throughout the wall surface. Obviously the tile was not adhered to the mortar bed and simply fell off when a lower row of tile was removed.
Additionally, The mortar bed would visibly flex when pulled or pushed on indicating that the deflection standards would not be met.
The mortar bed and remaining tile was removed. It was a blessing to find that the original studs and supporting framing were intact. New mortar beds were built and the tiled shower was replaced.