SI-COAT 579 CM Corrosion Maintenance Coating: Frequently Asked Questions

What is SI-COAT 579 CM and what is it used for?

SI-COAT 579 CM is a single component moisture cure RTV silicone corrosion maintenance coating manufactured by CSL Silicones. It protects structural steel, storage tanks, bridges, mining infrastructure, industrial equipment and pipelines from corrosion in harsh outdoor environments. Furthermore, it was specifically formulated as a surface tolerant coating for maintenance situations where conventional systems are not practical. It applies in a single coat without primer, bonds directly to hand and power tool cleaned steel, and delivers a service life exceeding 20 years in environments that destroy conventional epoxy and polyurethane coatings within five to seven years.

What is a surface tolerant coating and why does it matter?

A surface tolerant coating is a protective coating system formulated to adhere and perform correctly on steel that has not been abrasive blast cleaned to Sa2.5 near white metal standard. Most high performance coating systems specify Sa2.5 as their minimum surface preparation requirement because they rely on the deep anchor profile created by abrasive blasting to achieve adequate adhesion. In real world maintenance conditions on bridges, storage tanks, mining structures and in service industrial steel, abrasive blasting is frequently not achievable. Access constraints, operational requirements, environmental regulations, dust containment requirements and logistics all make blast cleaning impractical on many maintenance projects.

SI-COAT 579 CM addresses this directly. It bonds to steel prepared by hand tool and power tool cleaning to St2 or St3 standard under ISO 8501-1, without requiring abrasive blasting equipment. This makes effective corrosion protection achievable on in service structures where conventional high performance coatings simply cannot be used.

What is the difference between St2, St3 and Sa2.5 surface preparation?

These are internationally recognised surface cleanliness standards defined in ISO 8501-1, and understanding the difference is critical for specifying the correct coating system.

St2 is thorough hand and power tool cleaning. Wire brushing, disc grinding, needle guns and power tools remove poorly adhering mill scale, rust, paint and surface contamination. When viewed without magnification, the surface is free from visible oil, grease and dirt, and from poorly adhering mill scale, rust and paint. A slight metallic sheen remains after cleaning.

St3 is very thorough hand and power tool cleaning. The process follows the same approach as St2 but the operator goes considerably further. The result is a pronounced metallic sheen arising from the metallic substrate rather than a slight sheen.

Sa2.5 is near white metal blast cleaning achieved with abrasive blasting equipment and blast media. The surface is almost entirely free of all mill scale, rust, coating and foreign matter. Only slight staining remains in the form of spots or stripes. Sa2.5 produces a defined surface profile that conventional epoxy and polyurethane coatings need for mechanical adhesion.

SI-COAT 579 CM performs correctly from St2 upward. It does not require the anchor profile that Sa2.5 produces because silicone chemistry adheres through a different mechanism to epoxy. This is what makes it the practical corrosion protection solution for maintenance projects worldwide.

Can you apply a corrosion coating without sandblasting?

Yes. SI-COAT 579 CM bonds directly to steel prepared by hand tool or power tool cleaning to St2 or St3 standard under ISO 8501-1. No sandblasting or abrasive blasting equipment is required. Standard maintenance crews using wire brushes, angle grinders, disc sanders and needle guns can meet the surface preparation requirement that 579 CM needs to perform correctly. This makes effective corrosion maintenance achievable on bridges, storage tanks, industrial structures and mining infrastructure where abrasive blasting is not practical.

Why do most industrial coatings require Sa2.5 blast cleaning?

Conventional coating systems including epoxy and polyurethane need a high anchor profile created by abrasive blasting to achieve adequate mechanical adhesion to the steel substrate. Without that profile, adhesion is insufficient and the coating fails prematurely through delamination or osmotic blistering. SI-COAT 579 CM uses silicone chemistry that bonds effectively to hand and power tool cleaned surfaces at St2 and St3 because silicone forms a chemical bond with the substrate rather than relying purely on mechanical interlocking with a blast profile. Consequently, the deep anchor profile that epoxy systems require is not necessary for silicone to perform.

How long does SI-COAT 579 CM last?

On correctly prepared steel in harsh outdoor environments including coastal, industrial, mining and high UV conditions, SI-COAT 579 CM provides a service life exceeding 20 years. Epoxy systems in the same environments typically require recoating every five to seven years. Polyurethane systems carry a similar service life of five to eight years before UV degradation and coating fatigue require maintenance intervention. Over a 20 year asset life, silicone delivers total lifecycle costs 40 to 60 percent lower than conventional systems when recoating, labour, access and downtime costs all factor into the calculation.

How does SI-COAT 579 CM compare to epoxy and polyurethane coatings?

The comparison comes down to four critical performance factors that matter on real maintenance projects.

Surface preparation is the first. Epoxy and polyurethane systems require Sa2.5 blast cleaning for reliable performance. SI-COAT 579 CM requires St2 or St3 hand and power tool cleaning. On in service structures, that difference determines whether maintenance happens at all.

UV stability is the second. Epoxy coatings degrade under UV radiation through photo-oxidation, chalking and loss of flexibility. Polyurethane coatings yellow and degrade under sustained UV exposure. Silicone chemistry is inherently UV stable because the silicon oxygen polymer backbone does not respond to UV radiation the way carbon based organic polymers do. SI-COAT 579 CM does not chalk, yellow, crack or lose flexibility under any UV exposure level.

Flexibility is the third. Epoxy coatings are rigid and crack under the thermal cycling and structural movement that characterises in service steel. SI-COAT 579 CM remains permanently flexible, accommodating movement without cracking and without creating the hidden corrosion pathways that develop beneath failed epoxy films.

System complexity is the fourth. Epoxy corrosion protection typically involves a zinc rich primer, an epoxy intermediate coat and a polyurethane topcoat. SI-COAT 579 CM is a single coat system with no primer and no topcoat. One application provides both corrosion protection and a finished UV stable surface.

Is SI-COAT 579 CM a one coat system?

Yes. SI-COAT 579 CM provides complete corrosion protection and a UV stable finished surface in a single coat. No zinc rich primer is required. No epoxy intermediate coat is required. No polyurethane topcoat is required. For maintenance projects where access is constrained and application windows are limited, the difference between one coat and three is often the difference between a project that gets done and one that gets deferred.

Does SI-COAT 579 CM require a primer?

No primer is required when applying SI-COAT 579 CM to correctly prepared steel. The coating is self priming and bonds directly to steel prepared to St2 or St3 standard under ISO 8501-1. For C5 corrosivity environments such as marine or aggressive industrial zones where maximum long term corrosion performance is required, applying 579 CM over a zinc phosphate epoxy primer achieves C5-M and C5-I corrosion protection per ISO 12944-6. In those applications, priming is recommended to achieve the highest possible performance classification.

What corrosivity categories does SI-COAT 579 CM meet under ISO 12944?

Applied directly to St2 or St3 prepared steel without primer, SI-COAT 579 CM provides corrosion resistance suitable for C3 and C4 corrosivity categories per ISO 12944. These categories cover medium to high corrosivity environments including urban and industrial atmospheres, coastal areas with low salinity, chemical plants and swimming pools. Applied over a zinc phosphate epoxy primer to correctly prepared steel, SI-COAT 579 CM achieves C5-M marine and C5-I industrial corrosion protection per ISO 12944-6, meeting the most stringent international standards for the most aggressive environments.

What is C5 corrosivity and when is it relevant?

ISO 12944 defines corrosivity categories from C1 very low through to C5 very high. C5-I covers industrial environments with high humidity and aggressive atmospheres. C5-M covers marine environments and coastal areas with high salinity. These are the most demanding coating environments in the classification system and include offshore platforms, coastal industrial facilities, mining operations handling aggressive chemicals, and chemical processing plants. SI-COAT 579 CM achieves C5-M and C5-I classification when applied over zinc phosphate epoxy primer, making it suitable for the most demanding industrial and marine environments in Southern Africa and globally.

Can SI-COAT 579 CM be applied over existing paint or coating?

Yes. SI-COAT 579 CM can be applied over existing paint or coating systems where the existing coating has sound adhesion to the substrate. Areas of active delamination, blistering or poorly adhering coating should be removed and the substrate prepared to St2 or St3 standard before application. Sound existing coating that passes a pull off adhesion test can remain in place. The chemical inertness of silicone means it does not react adversely with most existing coating systems including epoxy, polyurethane and alkyd systems.

What substrates can SI-COAT 579 CM be applied to?

SI-COAT 579 CM bonds to structural steel, carbon steel, weathering steel, galvanised steel, concrete, and previously coated surfaces where the existing coating is sound. It is suitable for all structural and industrial steel substrates including beams, columns, plates, tanks, pipework, grating and handrails. On concrete substrates, the surface should be clean, sound and free from laitance, contamination and poorly adhering material before application.

How is SI-COAT 579 CM applied?

SI-COAT 579 CM applies by brush, roller or airless spray. It is a single component product requiring no mixing. Surface preparation to St2 or St3 standard is required before application. The coating is tack free within approximately 30 minutes under ambient conditions and fully cures within 7 to 14 days depending on temperature and humidity. Moisture cure means the curing process proceeds at ambient temperature and humidity without any requirement for elevated temperature or forced curing. Higher ambient humidity accelerates the cure rate.

What temperature and humidity conditions are required for application?

SI-COAT 579 CM applies in ambient temperatures from approximately 5 degrees Celsius upward. Moisture cure means it benefits from ambient humidity rather than being hindered by it, unlike two component polyurethane systems that have strict humidity application windows. The substrate should be dry and free from frost, ice, condensation and standing water at the time of application. The steel temperature should be at least 3 degrees Celsius above the dew point to prevent condensation forming on the surface during application.

Is SI-COAT 579 CM resistant to sulphuric acid?

Yes. SI-COAT 579 CM provides excellent resistance to sulphuric acid, making it specifically suitable for copper mining operations in Zambia, the DRC and South Africa where sulphuric acid from the heap leaching and solvent extraction process is present in the environment. It also resists a wide range of industrial acids, alkalis and chemical contaminants found in mining, chemical processing and petrochemical environments. For specific chemical resistance data on a particular concentration or combination of chemicals, contact Technical Solutions Supplies for technical guidance.

Is SI-COAT 579 CM suitable for mining environments?

Yes. Mining and mineral processing operations present some of the most aggressive corrosion environments in the world. Sulphuric acid from copper processing, salt spray in coastal mining operations, abrasive dust across the Copperbelt, and the combination of chemical and UV attack in open pit operations all create conditions that destroy conventional coatings rapidly. SI-COAT 579 CM resists chemical attack from the acids and alkalis encountered in mining processing environments, remains UV stable under direct sun exposure on surface infrastructure, and applies to in service equipment and structures without the blast cleaning logistics that operational mining environments cannot accommodate.

Is SI-COAT 579 CM suitable for coastal environments?

Yes. SI-COAT 579 CM is inherently resistant to chloride attack and does not hydrolyse or degrade in high humidity marine environments. Coastal industrial structures in KwaZulu-Natal, the Western Cape, coastal Namibia and Mozambique face aggressive salt aerosol deposition combined with high UV radiation. These two factors together accelerate the degradation of organic coatings significantly beyond inland service lives. Silicone chemistry is not subject to chloride induced degradation or UV induced photo-oxidation, making it specifically suited to coastal industrial environments where conventional coatings fail prematurely.

Is SI-COAT 579 CM suitable for bridges and overpasses?

Yes. Bridges and overpasses present some of the most challenging corrosion maintenance conditions in infrastructure. Access to steelwork is constrained and expensive. Traffic management during maintenance is a major operational and financial burden. Abrasive blasting on an active road structure generates dust and debris that creates logistical, safety and regulatory complications. The result is that conventional maintenance systems are repeatedly deferred on bridge infrastructure until failure occurs.

SI-COAT 579 CM addresses this directly. It applies to bridge steelwork prepared to St2 or St3 standard by standard maintenance crews within traffic management windows, without blast cleaning equipment. It remains permanently flexible to accommodate the structural movement and thermal cycling that bridges generate throughout their service life. It does not chalk or degrade under UV exposure on exposed fascia steelwork. Applied correctly, it provides corrosion protection across multiple maintenance cycles rather than requiring replacement within five to seven years.

Is SI-COAT 579 CM suitable for storage tanks?

Yes. Storage tanks on mining sites, petrochemical facilities, chemical plants and industrial facilities are prime applications for SI-COAT 579 CM. Tank external surfaces in industrial environments face chemical splash, UV exposure, thermal cycling and in many cases direct chemical contamination from process operations. SI-COAT 579 CM resists all of these without the performance degradation that organic coatings experience. Furthermore, applying to tanks during operational maintenance windows without full blast cleaning avoids the production downtime that conventional recoating programmes require.

Is SI-COAT 579 CM suitable for structural steel in chemical and petrochemical plants?

Yes. Chemical and petrochemical environments expose structural steel to acid splash, solvent contact, alkali exposure, and the combination of chemical attack with high UV and wide thermal cycling. SI-COAT 579 CM’s chemical inertness and silicone chemistry make it resistant to the full range of chemical contaminants found in these environments. It also applies without blast cleaning on in service plant structures where taking the asset offline for conventional coating preparation is operationally and commercially impractical.

Can SI-COAT 579 CM be used on pipelines?

Yes, for the external surface of above ground pipelines. SI-COAT 579 CM provides external corrosion protection for above ground structural and process pipework in mining, industrial and petrochemical environments. It resists the chemical splash, UV exposure, thermal cycling and condensation that cause conventional coatings on above ground pipework to fail prematurely. For below ground or submerged pipeline applications, contact Technical Solutions Supplies for specific guidance on the appropriate coating system.

What is corrosion under insulation and can SI-COAT 579 CM prevent it?

Corrosion under insulation, known as CUI, occurs when moisture penetrates insulation systems on pipelines and equipment, trapping water against the steel surface and accelerating corrosion at a rate that is not visible during routine inspection. SI-COAT 579 CM forms a moisture resistant barrier on the steel substrate beneath insulation systems. Its hydrophobic silicone chemistry resists the moisture penetration that drives CUI, and its flexibility accommodates the thermal cycling that occurs on insulated pipework without cracking or delaminating. This makes it a useful protective treatment for steel surfaces prior to insulation installation in environments where CUI is a known risk.

How does SI-COAT 579 CM perform in extreme temperatures?

SI-COAT 579 CM remains flexible and maintains its protective properties from below zero to above 200 degrees Celsius. Epoxy coatings become brittle at low temperatures and soften or fail at elevated temperatures. Polyurethane coatings have a narrower useful temperature range than silicone. The wide thermal tolerance of silicone makes 579 CM suitable for structural steel in environments with large daily temperature swings, for pipework and equipment operating at elevated surface temperatures, and for steel structures in extreme climate conditions.

Does SI-COAT 579 CM resist UV radiation?

Yes. Silicone chemistry is inherently UV stable. The silicon oxygen backbone of the polymer does not respond to UV radiation the way carbon based organic polymers do. Therefore, SI-COAT 579 CM does not chalk, yellow, lose flexibility or crack under sustained UV exposure regardless of intensity. This is particularly relevant in Southern Africa where UV radiation levels rank among the highest in the world. Conventional epoxy and polyurethane coatings on exposed structural steel in South Africa, Namibia and Zambia degrade significantly faster than temperate climate data sheets indicate. Silicone does not.

What is the lifecycle cost advantage of SI-COAT 579 CM compared to conventional systems?

A conventional epoxy or polyurethane coating system on exposed structural steel in a harsh Southern African environment requires recoating every five to seven years. Each recoating cycle generates surface preparation costs, material costs, application labour costs, scaffolding and access costs, and production downtime costs. Over a 20 year period, a conventional system generates three full recoating cycles. SI-COAT 579 CM applied once to correctly prepared steel delivers the same or better corrosion protection across the full 20 year period with no recoating required. Research consistently shows total lifecycle cost for silicone at 40 to 60 percent lower than conventional systems over a 20 year period when all maintenance and downtime costs are included in the calculation.

What VOC content does SI-COAT 579 CM have?

SI-COAT 579 CM is a low VOC coating. This is increasingly relevant as environmental regulations on solvent emissions tighten globally and as corporate sustainability commitments require asset owners to demonstrate lower environmental impact from maintenance programmes. Lower VOC content also reduces health and safety risks for application crews working in confined or poorly ventilated conditions on maintenance projects.

Does SI-COAT 579 CM meet international corrosion protection standards?

Yes. SI-COAT 579 CM complies with ASTM and ISO performance standards for corrosion protection coatings. Applied over zinc phosphate epoxy primer to correctly prepared steel, it achieves C5-M and C5-I corrosion protection classification per ISO 12944-6, which represents the most stringent international standard for protective coating systems on steel structures in marine and industrial environments. It also meets the performance requirements for surface tolerant maintenance coating systems under the relevant SSPC and NACE standards referenced in global infrastructure maintenance specifications.

Where is SI-COAT 579 CM available?

SI-COAT 579 CM is manufactured by CSL Silicones and distributed exclusively across Sub-Saharan Africa by Technical Solutions Supplies. We supply throughout South Africa, Namibia, Botswana, Zimbabwe, Zambia, Mozambique, Tanzania, Kenya, Uganda, Rwanda, Angola, the Democratic Republic of Congo, Malawi, Madagascar, Mauritius, Eswatini and Lesotho.

We cover the full Copperbelt corridor across Zambia and the DRC, where sulphuric acid corrosion from copper mining and processing operations makes SI-COAT 579 CM one of the most critical maintenance products available to asset owners and mine operators in the region.

We provide technical specifications, application guidance, product samples, contractor training and on site technical support for projects of all sizes across the continent. If your operation sits in Sub-Saharan Africa and you are dealing with corrosion on structural steel, storage tanks, bridges or industrial infrastructure, we can supply and support you.

Who should I contact for a technical specification or project quote?

Contact Technical Solutions Supplies directly for project specific technical guidance, coating system specification, application specifications and pricing.

Phone: 031 002 7376 Email: sales@tssupplies.co.za

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