Chunks of concrete are flaking off the pillars, beams, or external walls of your building. This is called spalling — and it is not just a cosmetic problem. It is a structural deterioration that accelerates over time.
Understanding what is happening and fixing it now prevents lakhs in repair costs later.
What Is Spalling Concrete
Spalling is the breaking away or flaking off of layers of concrete from the surface inward. The concrete loses its bond to the reinforcing steel beneath and begins to fracture and shed material.
It typically starts small — a patch the size of your palm — but if left unchecked, it spreads and deepens. Within a year or two, an area of spalling that was initially a centimetre deep can become 5–10 centimetres deep, exposing rebar and creating a structural weakness.
Why Does Concrete Spall in Mumbai Buildings
Spalling happens when one or more of three conditions are met:
Corrosion of reinforcing steel. Water and chlorides penetrate the concrete pores and reach the rebar. The steel oxidizes, expanding as it rusts. This expansion creates internal pressure that fractures the concrete around it from within, causing the surface to spall.
Freeze-thaw cycles. While Mumbai’s climate does not have true winter freezing, buildings in high-altitude areas and near coastal salt spray experience the freeze-thaw effect through salt crystallisation cycles — water with dissolved salts enters the concrete, then evaporates, leaving salt crystals that expand and contract with temperature and humidity changes.
Chemical attack from marine environments. Buildings within 500m of the sea in Worli, Mahim, Bandra, Juhu, and Colaba are in the “marine splash zone.” Airborne chlorides from seawater penetrate concrete continuously. Over 15–20 years, this leads to widespread rebar corrosion and spalling across large areas of the structure.
How to Identify Early-Stage Spalling
Before large chunks fall off, spalling announces itself:
— Small flakes or powder coming away from concrete surfaces
— Rust staining on the concrete surface (the rebar is bleeding through)
— Hairline cracks radiating around a patch (the concrete is fracturing around corroding steel)
— Hollow sounds when you tap the concrete (the bond between layers is already failing)
If you see any of these on pillars, beams, or external walls, spalling is underway. The time to repair is when the affected area is still small — 200–400 sq cm. Once it exceeds 1000 sq cm, repair becomes significantly more complex and expensive.
The Repair Sequence for Spalled Concrete
Patching spalled areas with fresh concrete rarely works. The new concrete and old concrete expand at different rates, and the underlying rebar — if it is corroded — continues to rust and push the repair off.
The correct sequence:
1. Remove all spalled and deteriorated concrete back to sound, solid material — typically 50–100mm deeper than the visible spalling. This is more aggressive than it looks, but it is necessary.
2. Assess and treat the rebar. If rebar is exposed and rusted, wire-brush it to remove loose rust. For moderate to heavy corrosion, apply a corrosion inhibitor or passivating coating that chemically stops further oxidation.
3. Apply a concrete repair mortar or microcement that has a similar expansion rate to the original concrete and forms a strong bond. Two-part epoxy or polyester repair mortars are commonly used for their high strength and chloride resistance.
4. Cure properly. Concrete repairs need time and moisture control. Rushing to re-expose the repaired area to water or load before curing is complete causes the repair to fail prematurely.
5. Protect the repair with a waterproof coating — either a cementitious waterproofing or an elastomeric membrane — to prevent water re-entry and further corrosion.
Is Spalling a Structural Concern
It depends on the location and extent:
— Spalling on a non-structural façade panel: primarily aesthetic, but indicates moisture is entering the building.
— Spalling on a structural column or beam: yes, this reduces the cross-sectional area of the structural member and its load-carrying capacity. Large or deep spalling on primary structural elements requires professional structural assessment and engineer-designed repairs.
— Spalling at construction joints or around utilities: often indicates water is concentrated at that point, signalling a waterproofing failure in the broader structure.
Any spalling deeper than 50mm or wider than 1 metre should be assessed by a structural engineer before repair.
Why Pre-Monsoon Repair Matters in Mumbai
Spalling accelerates dramatically during monsoon when concrete is continuously wet and water pressure forces chloride solutions deeper into the structure. A small spall in May becomes a large one by September if left unrepaired.
Getting ahead of spalling before the rains arrive — even with interim repairs if full repairs cannot be completed before June — prevents exponential deterioration.
Watch PS Group’s spalling concrete repair work on the PS Group YouTube channel. See completed repair projects in the PS Group gallery.
For a structural assessment of spalling on your Mumbai building, call +91 97684 16600 or WhatsApp PS Group. Full civil repair details at pscivil.com/civil. Where waterproofing of structural surfaces is needed alongside repair, see pscivil.com/waterproofing.
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