Cathodic protection is offered as a cure for corroding concrete and buried steel. Understanding its actual mechanism tells an owner when it is the right answer.
Cathodic protection works by making the metal you want to protect the cathode in an electrical circuit, so that corrosion occurs elsewhere, either at a sacrificial anode that is consumed or at an inert anode supplied with current. It is a genuine engineering technique used on buried pipework, tanks and chloride contaminated concrete. It is also sold loosely, which is why owners need to understand the mechanism before buying.
How to test a claim like this
Ask three questions of any cathodic protection proposal. What is being protected, specifically, and is it a continuous electrically connected metal element? How will protection be verified, by what measurement, at what intervals, and who performs it? And what happens to the system in ten years, including anode replacement, power supply maintenance and monitoring. A proposal that cannot answer the second question is selling equipment rather than protection.
Myth 1: Cathodic protection repairs corrosion that has already happened.
Reality: It arrests or slows further corrosion of the protected steel. It does not restore section that has already been lost, nor does it repair concrete that has already cracked or spalled. Structural repair of damaged areas still has to happen, and the protection system then prevents the surrounding areas from deteriorating in the same way.
How to check it yourself: Separate the repair scope from the protection scope in the specification and in the pricing.
Myth 2: It can be applied to any structure that is corroding.
Reality: The technique needs an electrically continuous metal element and a medium that conducts, such as soil, water or concrete. Reinforcement that is not continuous across a structure cannot be protected as one system, and isolated elements need their own arrangements. A survey of electrical continuity is a prerequisite, not an optional extra.
How to check it yourself: Require a continuity survey result before any design is priced.
Myth 3: Once installed it works without attention.
Reality: Sacrificial anodes are consumed and must eventually be replaced. Impressed current systems need a power supply, cabling and a transformer rectifier that can fail silently, leaving the structure unprotected while the installation looks intact. Protection is confirmed by measurement at reference electrodes, not by the presence of equipment.
How to check it yourself: Ask for the monitoring regime, the measurement criterion and the last set of recorded readings.
Myth 4: It is only used on pipelines and marine structures.
Reality: Those are the classic applications, but it is also applied to chloride contaminated reinforced concrete in buildings, to buried tanks, to fire water pipework and to car park structures where de icing or sea air has driven chloride into the slab. In buildings, the usual alternative is extensive concrete replacement, which is frequently more disruptive and more expensive.
How to check it yourself: Compare the cost against the realistic extent of concrete replacement, not against doing nothing.
Myth 5: Any corrosion contractor can design the system.
Reality: Design requires current demand calculations, anode placement, continuity provision, monitoring design and criteria for proving protection. Badly designed impressed current systems can cause problems of their own, including interference with nearby buried metal. This is a specialist discipline with its own standards and qualified practitioners.
How to check it yourself: Ask for the qualifications of the designer and the standard the design follows.
Myth 6: It removes the need for other corrosion controls.
Reality: It protects the steel it is connected to, and nothing else. The coating regime, drainage details, the exclusion of further chloride, washing of exposed surfaces and sound construction detailing all remain necessary. A protected structure that continues to be soaked in chloride needs more current over time and still deteriorates at any element outside the system.
How to check it yourself: Keep the normal maintenance regime in the plan alongside the protection system.
What this changes in your decision
- Commission a corrosion survey, including continuity testing, before considering any protection system.
- Separate the repair of damaged areas from the protection of sound areas in both scope and price.
- Require a written monitoring regime with a measurement criterion and a responsible party.
- Budget for anode replacement and for maintaining the power supply and monitoring equipment.
- Retain the readings as a dated record, since they are the only evidence that protection is working.
Domira works on buildings that already exist: surveying what is installed, specifying the systems that have to be replaced, and running maintenance and refurbishment work around the people using the property. Tell Domira which asset you are responsible for and we will say what we would inspect first.
Frequently Asked Questions
When is cathodic protection worth considering for a building?
Typically when chloride contamination is widespread in reinforced concrete and conventional patch repair would either be impractical in extent or would accelerate corrosion adjacent to the repairs. Car park decks, coastal frames and structures with a long history of leaking are common candidates. A corrosion survey establishes whether the conditions for the technique are actually present.
What is the difference between sacrificial and impressed current systems?
A sacrificial system uses anodes of a more reactive metal that corrode in place of the steel and are consumed over time, with no external power. An impressed current system uses inert anodes and a power supply to drive the protective current, which allows control and monitoring but requires electricity, equipment and ongoing attention. The choice follows the size and the current demand.
How is it proved that cathodic protection is working?
Through measurement at reference electrodes installed within the structure, against criteria set by the applicable standard, recorded at defined intervals. Equipment that is energised is not evidence. Ask for the readings, their dates and the criterion being applied, and keep them in the building file, because they are what a future purchaser or engineer will need.
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