Choosing a corrosion protection coating is one of the biggest decisions an asset manager, engineer or maintenance contractor makes. Corrosion costs South Africa dearly. The Corrosion Institute of Southern Africa puts the direct cost at about 4% of GDP, with indirect costs at least three times higher. Steel structures, pipelines, tanks, bridges and plant all deteriorate when left unprotected, and salt spray, chemical exposure, strong UV and wide temperature swings speed that up.
Get the coating right, and critical assets stay protected for many years. Get it wrong, and the cycle of early failure, recoating and unplanned downtime starts.
This guide covers the coating types available, how to choose between them, and why silicone deserves a place in specifications that default to epoxy.
Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles. That includes Si-COAT 579CM, a silicone corrosion maintenance coating.
What Is a Corrosion Protection Coating?
A corrosion protection coating is a barrier on steel or other metal. It keeps moisture, oxygen and corrosive chemicals away from the surface. Without it, steel reacts with moisture and oxygen to form rust, which weakens the metal over time.
Coatings protect in two main ways. Barrier protection physically separates the steel from its surroundings. Sacrificial protection uses zinc, which corrodes in place of the steel and protects it even where the film is damaged.
Classic heavy duty systems combine both: a zinc-rich primer for sacrificial protection, then intermediate and top coats for barrier and UV protection. However, that multi-coat approach does not suit every job. On many assets already in service, a single coat, surface-tolerant system gives better value over the life of the asset.
What Types of Coating Are Available?
Several coating chemistries compete in the South African market. Each has strengths and limits that decide where it fits.
Zinc-rich primers use zinc dust that corrodes in place of the steel. They give excellent active protection, but they usually need abrasive blasting to near-white metal. That is a real constraint on sites where blasting is impractical or not allowed.
Epoxy coatings form a hard, chemically resistant film with strong adhesion on properly prepared steel. However, epoxy is rigid. Heat cycles crack it, moisture gets under the film, and corrosion follows. In strong UV, its surface also chalks, so it needs a topcoat outdoors.
Polyurethane coatings usually go on as a topcoat over epoxy and handle UV better. Still, polyurethane is also rigid, so it does not suit surfaces that move or cycle hard in heat.
Alkyd and oil-based coatings are lower cost options for mild conditions. They do poorly in aggressive industrial, coastal or chemical exposure, so they do not suit long-term protection of critical assets.
RTV silicone coatings work differently. Silicone is elastomeric, so it flexes with the steel instead of cracking. It bonds to sound existing coatings and tightly adhered rust without blasting, and it resists UV for the life of the film. Si-COAT 579CM is the RTV silicone corrosion maintenance coating from CSL Silicones.
How Do You Choose the Right Corrosion Protection Coating?
Choosing the right coating comes down to four factors: the corrosion environment, the condition of the steel, the site constraints and the service life you need.
Corrosion environment. Coastal salt spray, industrial fumes and acid process chemistry each place different demands on a coating. ISO 12944 sorts environments from C1, very low, to C5, very high, with CX above that. In South Africa, many industrial and coastal sites sit between C3 and C5. For C5 sites, specify the Si-COAT CM System, which pairs Si-COAT 579CM with CSL 979 primer and passed ISO 12944-6:2018 testing for C5 High.
Condition of the steel. New steel in a fabrication shop can be blasted, so any system can be specified. However, steel on bridges, plant and structures in service often cannot stop for blasting. For these, a surface-tolerant coating is the practical option. Si-COAT 579CM goes onto steel prepared to SSPC SP2 hand tool cleaning, SSPC SP3 power tool cleaning or SSPC SP12 water jetting to WJ-4.
Site constraints. Abrasive blasting creates dust, noise and debris, which cause problems near people and running plant. Multi-coat systems also need overcoat windows that stretch the programme. By contrast, a single coat with simpler preparation shortens the job. At Reliant Energy in Texas, for example, tower projects that took four months came down to six weeks.
Service life. Upfront price says little on its own. A cheaper coating that needs frequent recoating can cost far more over the life of the asset. Our benchmark for Si-COAT 579CM is about 20 years, based on a CSL Florida power plant pipe coated in 2003.
What Is the Best Corrosion Protection Coating for Outdoor Steel Structures?
For outdoor steel, the best coating is the one that handles that site’s failure modes, not simply the most common specification.
Epoxy systems outdoors fail mainly in two ways: UV chalking and cracking from heat cycles. South Africa’s strong sun breaks down epoxy surfaces faster than in cooler climates. In addition, daily temperature swings crack rigid films at welds, fasteners and joints. Moisture then enters, and corrosion starts under the film, out of sight until blisters appear.
Si-COAT 579CM handles both. With 180% elongation, it flexes with the steel. It also showed no degradation after 5,000 hours of accelerated UV weathering. In the 36 month Florida Fence Test, it went onto hand tool cleaned rusted steel with no primer and showed no rust creep. Meanwhile, three coat zinc, epoxy and polyurethane systems on blasted steel did. That makes it a strong fit for transmission towers, bridges, pipe racks and industrial steelwork.
How Do You Prepare a Metal Surface for Corrosion Protection Coating?
Surface preparation is the biggest single factor in coating performance. Even the best system fails early on a poorly prepared surface.
For new steel getting a conventional multi-coat system, the usual standard is abrasive blasting to near-white metal. That removes mill scale, rust and contamination, and leaves an anchor profile for adhesion.
For steel in service where blasting is impractical, Si-COAT 579CM accepts hand tool, power tool or water jet cleaning. First, remove oil, grease, dirt and salts. Then remove loose rust, loose mill scale and any paint that is peeling or blistering. Old coating that stays must pass the ASTM D3359 tape test at 4A or 4B. Tightly adhered rust that hand or power tools cannot lift can stay.
Next, brush a stripe coat of about 0.13 mm dry (5 mil) onto edges, welds and bolts. Then apply one full coat of about 0.2 to 0.5 mm once dry (8 to 20 mil). In every case, the surface must be clean, dry and at least 3°C above the dew point.
How Long Does a Coating Last?
Service life depends on the chemistry, preparation, thickness and exposure. In aggressive coastal, industrial or mining conditions, alkyds wear out first. Epoxy systems last longer, especially with a good topcoat, but outdoors they still crack and chalk over time. Full zinc, epoxy and polyurethane systems last longest of the conventional options, provided the steel was blasted and the work done correctly.
For Si-COAT 579CM, our benchmark is about 20 years. CSL’s longest running reference is a Florida power plant pipe coated in 2003, which still protects its steel. It has also passed the 36 month Florida Fence Test with no rust creep.
What Is the Cost of Corrosion Protection Coating in South Africa?
The cost has two parts: the upfront job, and the maintenance over the life of the asset.
Upfront cost depends on area, preparation, coating system and labour. Multi-coat epoxy with abrasive blasting usually costs more upfront than a single coat, surface-tolerant system on hand or power tool cleaned steel.
Lifecycle cost matters more, though. Every recoat brings preparation, materials, labour and disruption again. Documented projects show the difference. When Florida Power and Light coated a large fuel oil tank with Si-COAT 579 in 2002, the project cost about 50% of a traditional coating system. It also took three weeks, against at least two months for a conventional system.
For pricing on your project, contact us.
Mining Applications
Mines are some of the toughest places for steel. Acid process chemistry, humid underground workings, abrasive ore handling, strong UV in open pits and constant vibration all wear conventional coatings out early.
Si-COAT 579CM has a strong mining record. At the Escondida copper mine in Chile, it replaced failed epoxy in desert, high altitude conditions. CSL also coated sulphuric acid transport tanks for CODELCO in Chile. Closer to home, our case studies cover a fertiliser plant and a chlorine plant. Around acid, it handles vapour and occasional splash. However, it is not for pooling or immersion. For more, see our article on mining corrosion protection.
Coastal and Marine Environments
South Africa’s coastline runs from the cold Atlantic off the Western Cape to the warm Indian Ocean off KwaZulu-Natal. Salt spray travels well inland, so coastal plants corrode much faster than similar plants inland.
Si-COAT 579CM passed 3,000 hours of ASTM B117 salt fog and the Florida Fence Test on the Atlantic coast. Its water-repellent silicone surface also sheds moisture. That suits port structures, coastal bridges, equipment housings and plant in salt spray zones. On the worst marine exposures, however, specify the CM System with CSL 979 primer.
Frequently Asked Questions
What is anti-corrosion coating?
An anti-corrosion coating is a protective layer on steel and other metals. It blocks moisture, oxygen and corrosive chemicals from reaching the surface. Good ones combine adhesion, chemical resistance and enough flexibility to move with the structure without cracking.
Does corrosion protection coating work on rusty steel?
Conventional coatings usually need the rust removed first. Surface-tolerant coatings like Si-COAT 579CM work differently. After you remove loose rust and scale, it bonds to the tightly adhered rust that remains and seals it in. That works because silicone forms chemical bonds with the surface, rather than relying only on a blast profile.
What is the difference between corrosion protection coating and rust paint?
Rust paint is a loose term for any paint sold for rusty metal, often a low cost alkyd. A corrosion protection coating is engineered for a specific environment, with tested adhesion, flexibility, chemical resistance and weathering. Si-COAT 579CM falls in the second group.
How do I choose a corrosion protection coating supplier in South Africa?
Look for documented case histories in your type of environment, real technical support and a range that suits your corrosion category. Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles, with application guidance and on site support.
Is silicone better than epoxy for corrosion protection?
For steel in service in harsh conditions, especially where heat cycles, UV and acid exposure combine, silicone has the edge on flexibility and UV resistance. Epoxy remains a strong option for new fabrication with full blasting in moderate environments. The right choice depends on the environment and the condition of the steel.
The Corrosion Protection Coating South Africa’s Infrastructure Needs
Corrosion’s cost to South Africa is not inevitable. The right corrosion protection coating, specified for the environment and the steel, extends asset life, lowers maintenance and cuts unplanned downtime.
Si-COAT 579CM offers one coat, simpler preparation and a benchmark of about 20 years, from coastal salt spray to mine acid vapour to high UV plant. For the harshest sites, the CM System adds C5 High performance.
To discuss your assets, contact us, read the Si-COAT 579CM FAQ, or see our article on anti-corrosion coating for structural steel.
Proud exclusive distributor of CSL Silicones in Southern Africa.