Why does spalling come back after repair?

Answer

Usually because the repair did not deal with the cause. BCA's PSI guidelines warn that incorrect repair procedures or unsuitable materials let spalling continue to deteriorate unseen under fresh coats of repair. Common faults are not removing all carbonated or contaminated concrete around the bars, not cleaning the steel, using ordinary plaster instead of a repair mortar, and leaving a leak or high humidity untreated.

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.

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Key facts

Main cause in homes: Carbonation leading to corrosion of steel bars in the ceiling slab
HDB reports after the defects period: About 13 cases per 1,000 flats a year (MND, 2018)
Minor vs structural spalling (BCA PSI template): Under 300 mm in longest direction: minor; over 300 mm: structural defect
HDB Goodwill Repair Assistance: HDB arranges repair and co-pays 50% (as stated by MND)
HIP essential improvement: Repair of spalling concrete and structural cracks, fully funded for Singapore Citizens

Defects and maintenance

Popped tiles, cracks, spalling concrete, roof and inter-floor leaks, window and glass safety, and the exterior features owners are legally responsible for: what causes them, when they are dangerous, and who has to fix them.

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Planning works like this?

RRD surveys the site, lists cost risks before you sign and plans the approvals first.

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Why does spalling come back after repair?

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