Who pays to repair spalling concrete in a condominium?
BCA's summary of the 2018 strata law amendments states that key structural elements, including foundations, beams and columns, are common property, and that slabs, excluding underlayment, are common property. Spalling of these structural elements is therefore generally for the MCST to repair under its duty to maintain common property. Confirm against your strata title plan and raise it in writing with the managing agent.
From the RRD Field Guide, checked against the sources cited in Concrete Spalling in Singapore: Causes, Risks, Repair Methods and Who Must Fix It. General information, not advice for your project.
The fuller picture
Spalling concrete is concrete cover cracking and breaking away because the steel reinforcement inside has corroded, usually after carbonation or chlorides destroy the steel's natural protection. Small patches can be repaired by removing loose concrete, cleaning and priming the steel and patching with polymer-modified mortar. Extensive spalling, beams, columns or cantilevers need a Professional Engineer. Owners repair inside HDB flats; MCSTs repair common property.