WHAT IS SPALLING? The condition shown in the image below is common in older buildings, bridges, and other concrete structures. Buildings on the KZN coast, are particularly susceptible to spalling, due to the extreme coastal weather conditions. The term “spalling” is used to describe this condition and specifically refers to the delaminating or fragmenting of the concrete surface.


Spalling in concrete can be triggered by several causes: The most prominent cause in KZN is sea salt or sodium chloride. Salt acts as a catalyst to enhance the reaction between the oxygen in the water and the iron in reinforcing steel. The resultant oxidation (rusting) causes the reinforcing steel to enlarge which creates high internal stresses within the concrete and, ultimately, the fracturing of the concrete surface.

Rusted steel can expand up to five times its original size.

Surface cracking can be generated by the reaction between atmospheric carbon dioxide and the alkalis present in the concrete mix itself. These surface cracks can then admit rainwater or condensation.


Concrete spalling can result in a variety of undesirable outcome: Spalls on the underside of concrete decks (bridges, general slabs etc.), can cause damage below as well as unsafe conditions. Falling concrete debris is also unsafe where pedestrians travel, (especially to spalling on vertical surfaces of buildings) and in parking areas. Spalled surfaces can lead to rapid degradation of reinforcing steel which would jeopardize the integrity of structures and necessitate costly repairs. Spalls are also unsightly and indicate a lack of maintenance on the part of facility owners or managing agents.


Casablanca – Durban:

Chipping & Priming: Once the spalling area has been chipped until fresh rebar has appeared, the concrete as well as the rebar are pre-saturated and primed.

Packing & Cross-Hatching: The primed area is then packed with a cementitious mortar and cross-hatched to allow for proper grip when skimming.

Skimming & Finish: The final product is then skimmed and smoothed off which can then be primed and painted.

Typically, an engineer is called in to oversee repairs. This includes identifying the areas to be repaired and writing specifications. Delaminated areas which have not yet broken loose can be detected by sounding methods, both mechanical and electronic. These areas as well as visible areas of spalls are marked for partial demolition. Possible shoring of existing structures must be evaluated and put in place before any demolition is performed. This can be pinning, using stainless steel rods, carbon reinforcement and specialist concrete repair mortars.
Demolition consists of saw cutting the perimeter of damaged areas taking care not to cut any existing rebar. Electric mechanical chipping tools are used to remove the damaged concrete, usually deep enough to provide about 2,5cm of clearance behind existing reinforcing steel so that the new patching material will have a good bond to the reinforcing steel. A good indicator is to make sure a finger can go comfortably around and behind the rusted steel. The steel is then mechanically cleaned to remove all rust.
Replacement of bars with some section loss may be required. After the bars are prepared, an epoxy coating may be required by the engineer. The existing concrete surface requires preparation in the form of cleaning and application of a bonding agent or keeping continuously wet for a specified period. Several patching compounds are available including speciality concrete materials or standard concrete mixes. The application will depend on the size, thickness and location of the area to be repaired. It may require a standard formed and poured concrete (shuttered) repair or a dry-packed or troweled-on patch.
Check out the very informative video below for some insight on what spalling is and how it works:

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