Due to the present significant need to repair and maintain our buildings and the building repair sector’s minimal experience in special structural elements, we here describe a study on the repair of ceramic violin joist slabs in an actual intervention on a building erected in the 1950s that had been unsuccessfully repaired several times. Due to damp and being close to the sea, the main reinforcement elements had undergone considerable corrosion causing a significant risk to the building’s safety. The intervention necessarily involved replacing the affected steel rebars with appropriate elements with mechanical and corrosion resistance properties, as required by the latest building codes. An appropriate strengthening and repair system was developed with a stainless steel prosthesis fitted to the lower third of the joists that almost tripled their resistance, gave them 120 min of fire resistance, and increased their durability against corrosion at a cost of less than 50% of the current repair systems with minimum generation of construction waste. One of the most appealing characteristics of this new repair system is its avoidance of the full replacement of the joists, which can be considered as a relevant contribution to the sustainability of the construction industry.