9 March 2022 - 17:16, by , in concrete repair, No comments

The body corporate management of this property contacted Singapore Waterproofing to inspect and remediate a concrete slab edge with signs of spalling concrete*. Based on our inspector’s assessment, the spalling concrete along the slab edge is caused by water leaking through the floor/wall joint from the lawn and planter box area directly above the slab.

During the inspection, our inspector discovered guttering installed right underneath the slab edge. This additional spalling was caused by the guttering. In close proximity to the concrete slab, the guttering created a humid environment. Continuing to soak the concrete resulted in rust and expansion of the supporting internal reinforcement steel, leading to spalling concrete/concrete cancer.

Additionally, we found two leaking pipe penetrations, a concrete crack, and a leaking cold joint over the divining wall in the garage. For all of these reasons, we recommended injecting hydrophilic polyurethane resin under high pressure into targeted areas for sealing. Our injection process creates a continuous three-dimensional seal buried in concrete using a combination of proprietary methods honed over thousands of projects.

To repair the spalling concrete, the leaking pipe penetrations, cold joint and concrete cracks, we recommended the following to rectify the concrete defects and water ingress:



  1. Remove render to expose the floor/wall joint.
  2. Perform leak sealing injection of floor/wall joint with hydrophilic polyurethane resin.
  3. Remove guttering along the slab edge.
  4. Perform concrete repairs along both sides of the slab edge.
    • Replace damaged reinforcement steel (reo/rebar).
    • Apply a rust inhibitor and primer is to the steel and exposed concrete.
    • Install formwork to support the installation of the repair mortar.
    • Install the shrinkage compensated structural mortar to the repair zone.
  5. Perform leak sealing injection of 2 pipe penetrations and 1 concrete crack with hydrophilic polyurethane resin.
  6. Perform leak sealing injection of cold joint over dividing wall in the garage with hydrophilic polyurethane resin.

Water ingress has been successfully stopped with leak sealing injections, and guttering does not need to be replaced. Job site cleanup included repainting.


The deterioration of steel-reinforced concrete is generally characterized by the appearance of cracks and corrosion. In severe cases, concrete sections completely separate from the steel reinforcing, thereby exposing the steel reinforcing to the elements. Spalling is often referred to as “concrete cancer”, as (like cancer) the issue isn’t evident at first, and as the problem advances, treatment becomes more difficult and more expensive.



  • Flaking, crumbling, spalling, expanding concrete
  • Rust Stains leaking out of the concrete
  • Bubbling, blistering, plating of concrete render
  • Leaks in overhead concrete surfaces
  • Rusting and exposed reinforcement pushing concrete so that it cracks and becomes loose


The challenge is that the visible signs of concrete cancer and spalling concrete often hide more extensive damage than is evident from the surface.

Gutter-and-signs-of-spalling-concrete on concrete slab edge

Gutter and signs of spalling concrete slab edge


Gutter removed and excavation of spalling concrete started

Gutter removed and excavation of spalling concrete started



Several factors predetermine the risk of concrete cancer, including proximity to the coastline and a built-up environment; the degree of concrete cover to steel reinforcing; the presence of differential metals; the quality and density of coating systems; inadequate waterproofing; building defects such as cracking; inefficient joint and penetration detailing and the level of preventative maintenance.

Some of the most common locations one can find corrosion of reinforcement steel are in columns and beams with the primary cause being lack of concrete cover to protect the steel and/or poor-quality concrete. Other common areas of water-driven concrete cancer are basements, underground car parks, flat concrete rooftops and balconies.

Corrosion of reinforcing steel or other embedded metals is by far the leading cause of premature ageing, deterioration and durability issues in concrete. Concrete cancer can happen in many areas of a concrete structure, so carrying out regular inspections is important. Identifying tell-tale signs at an early stage means that issues can be remedied before they become serious and start affecting the structural integrity of the building.

To help prevent spalling from occurring in cured, new concrete, cracks and holes should be adequately sealed as soon as possible. A crack that is identified as small and fine, can be repaired by v-cutting with a concrete crack chaser and filled with suitable material.

Depending on the depth and/or width of the crack, certain concrete cracks may best be repaired by targeted injection of appropriate material (i.e. suitable epoxy or polyurethane resins) tailored to the individual crack’s diagnosis – followed by a suitable protective concrete coating.

A protective coating, a penetrative concrete sealer or a waterproof membrane will provide a barrier against moisture, salts and chemical attacks. This will help improve the durability of the surface and prevent a corrosive environment from developing around the reinforcement.

The goal is to ensure that the long-term integrity of the concrete elements is not compromised.


When spalling concrete/concrete cancer has been repaired, it is important to take preventative steps to ward off a recurrence. We recommend implementing a maintenance program tailored for the environment the building is subjected to including dedicated inspections. Regular maintenance checks will help identify any problems in the early stages for repairs, which again will help enhance the service life and reduce the life cycle cost of concrete structures.

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