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

These are the questions we hear most about Si-COAT 579CM, a corrosion maintenance coating made by CSL Silicones. Every figure here comes from the CSL technical data sheet or from documented field work. If your question is not here, contact us.

What is the Si-COAT 579CM corrosion maintenance coating used for?

Si-COAT 579CM is a single component, moisture cure RTV silicone coating. It protects weathered and rusted structural steel, tank exteriors, bridges, machinery, cladding and metal roofs above ground. CSL designed it for retrofit work on structures that stay in service. As a result, it goes on in one coat over hand or power tool cleaned steel, with no abrasive blasting.

What is a surface tolerant corrosion maintenance coating?

A surface tolerant coating bonds and performs on steel that nobody has blast cleaned. Most heavy duty systems rely on the anchor profile that blasting leaves behind. However, on bridges, working plants and tanks in service, blasting is often impractical. Access, dust containment and shutdowns all get in the way.

Si-COAT 579CM solves this. The TDS accepts SSPC SP2 hand tool cleaning, SSPC SP3 power tool cleaning or SSPC SP12 water jetting to WJ-4. So a normal maintenance crew can prepare the steel inside a normal maintenance window.

What is the difference between St2, St3 and Sa 2½?

These are surface cleanliness grades from ISO 8501-1. St2 is thorough hand and power tool cleaning. It removes loose mill scale, rust and paint, and leaves a slight metallic sheen. St3 goes further and leaves a clear metallic sheen. Sa 2½ is near white metal blast cleaning, with only light staining left.

The American SSPC standards cover similar ground. Roughly, SSPC SP2 matches St2, SSPC SP3 matches St3, and SSPC SP10 matches Sa 2½. The Si-COAT 579CM data sheet uses the SSPC grades, and it works from SP2 upward. In other words, it does not need near white metal blasting.

Can you apply a corrosion maintenance coating without sandblasting?

Yes, with Si-COAT 579CM. Wire brushes, grinders, needle guns or a water jetting unit reach the surface standard it needs. First, remove dirt, grease, loose rust, loose mill scale and any peeling or blistering paint. Then coat. In the Florida Fence Test, CSL applied it straight onto rusted steel cleaned by hand tools only, with no primer.

Why do most industrial coatings need blast cleaning?

Epoxy and polyurethane systems rely mainly on mechanical grip. They need the rough anchor profile that blasting creates. Without it, they tend to lose adhesion, blister and peel. Silicone works differently, because it forms chemical bonds with the surface. Therefore, Si-COAT 579CM does not depend on a blast profile to hold on.

How long does the corrosion maintenance coating last?

Our benchmark is about 20 years. CSL’s longest running reference is a Florida power plant pipe coated in 2003. It has faced salt air and chemical spray since then and still protects the steel. In addition, it passed a 36 month Florida Fence Test with no rust creep, bleed through, pinholes or loss of adhesion. Of course, real life depends on preparation, thickness and exposure.

How does Si-COAT 579CM compare with epoxy and polyurethane?

Four things set it apart. First, preparation: conventional systems usually need blasting, while Si-COAT 579CM goes onto hand or power tool cleaned steel. Second, UV: organic topcoats chalk and fade over time. By contrast, Si-COAT 579CM showed no degradation after 5,000 hours of accelerated UV weathering to ASTM G154.

Third, flexibility: with 180% elongation, it moves with the steel instead of cracking. Finally, system size: a conventional system often means a zinc rich primer, an epoxy middle coat and a polyurethane topcoat. Si-COAT 579CM does the job in one coat.

Is Si-COAT 579CM a one coat system?

Yes. One coat gives both corrosion protection and a UV stable finish. That said, first brush a stripe coat of about 0.13 mm dry (5 mil) onto edges, welds, bolts, corners and pitted areas. Then apply the full coat over everything. The stripe coat matters, because edges and welds are where corrosion starts.

Does the corrosion maintenance coating need a primer?

Not for standard maintenance work. Si-COAT 579CM primes itself on most common substrates. Still, CSL recommends a quick field adhesion test before you start. For C5 environments, however, CSL pairs it with CSL 979 Corrosion Maintenance Primer. That combination is the Si-COAT CM System, covered below.

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

The Si-COAT CM System holds the ISO result. That system is CSL 979 primer at about 150 microns plus Si-COAT 579CM at about 150 microns. An independent laboratory tested it to ISO 12944-6:2018 for C5 High, over 1,680 hours and 10 cycles. It also passed 2,500 hours of ASTM B117 salt spray.

Si-COAT 579CM on its own does not carry an ISO 12944 category. Instead, its own evidence is the 36 month Florida Fence Test and 3,000 hours of ASTM B117 salt fog.

What is C5 corrosivity and when is it relevant?

ISO 12944 sorts environments from C1, very low, up to C5, very high, with CX above that for extreme offshore sites. C5 covers coastal sites with high salt and heavy industry with aggressive atmospheres. “High” durability means 15 to 25 years before major maintenance. So, for coastal plants and harsh industrial sites, specify the Si-COAT CM System with CSL 979.

Note that CSL 979 is less forgiving than the topcoat. CSL recommends blasting to SSPC SP6 or Sa 2 under it, although power tool cleaning may do on some maintenance work. It also needs 25°C to 40°C and relative humidity below 75%.

Can Si-COAT 579CM go over existing paint?

Yes, where the old paint is sound. First, remove anything peeling, flaking, cracking, blistering or lifting. Any old coating you keep must pass the ASTM D3359 tape test at 4A or 4B. Then feather back lifted edges. In CSL testing over an aged coating, the old paint cracked in bend and impact tests. However, the Si-COAT layer on top bridged those cracks without damage.

What substrates suit this corrosion maintenance coating?

It suits weathered and rusted structural steel, galvanised steel, metal roofs, cladding and sound existing coatings. On every new substrate, do a field adhesion test first.

On site, we have also carried it from concrete plinths straight onto the steel in one continuous coat. That way, there is no joint at the base for water to get into. Before you do, remove laitance, release agents and any wax or resin based curing compound, because it will not bond to them.

How is the corrosion maintenance coating applied?

It is one part, so there is nothing to combine. Stir it with a powered agitator for at least 5 minutes. Next, brush the stripe coat onto edges and welds. Then apply about 0.2 to 0.5 mm once dry (8 to 20 mil). That works out to roughly a third to three quarters of a litre per square metre, before losses.

CSL recommends airless spray, although brush or roller suit smaller areas. At 25°C and 50% humidity, it skins over in 25 minutes and is tack free in 60 minutes. It dries in 4 to 6 hours and reaches full properties in 7 days.

What temperature and humidity does application need?

Keep the surface between 5°C and 60°C and at least 3°C above the dew point. The steel must also be dry, with no frost or condensation. Because it is moisture cure, normal humidity helps it cure. In very humid or hot weather, however, use a pail lid with an agitator. That stops the product skinning over in the pail.

Is Si-COAT 579CM resistant to sulphuric acid?

It handles acid vapour and occasional splash in acid plants. Our sulphuric acid and fertiliser plant case studies show this in practice. In addition, CSL coated sulphuric acid transport tanks for CODELCO in Chile. However, CSL did not design it for pooling or immersion. So where severe splashing or pooling is likely, ask us and we will confirm suitability with CSL.

Is Si-COAT 579CM suitable for mining environments?

Yes, for steel above ground. Mine plant, conveyors and tanks face dust, moisture, process fumes and strong sun. They also rarely come out of service for blasting. For example, at the Escondida copper mine in Chile, it replaced failed epoxy in desert, high altitude conditions.

Is this corrosion maintenance coating suitable for coastal environments?

Yes. It passed 3,000 hours of salt fog and the 36 month Florida Fence Test on the Atlantic coast. On coastal sites, also check chloride levels on the steel. After water jetting, the TDS limits chlorides to below 7 ppm (10 µg/cm²). For the very worst marine exposures, however, specify the Si-COAT CM System with CSL 979.

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

Yes. CSL lists bridges as a typical use. On bridges, access is costly and blasting next to live traffic creates dust and safety problems. As a result, crews can prepare the steel with hand or power tools inside a traffic window. Its flexibility also suits the movement and heat cycles that bridge steel goes through.

Is Si-COAT 579CM suitable for storage tanks?

Yes, for tank exteriors. For example, Florida Power and Light coated an 85 metre fuel oil tank with it in 2002. In addition, our case studies include a crude oil tank in Athens. Because you avoid blasting, the work can often happen while the tank stays in service.

Is Si-COAT 579CM suitable for chemical and petrochemical plants?

Yes, for structural steel in airborne chemical exposure. CSL rates it for excellent tolerance to airborne chemicals. The TDS also lists resistance to engine oils and fuels for 14 days, alcohols for 7 days and acetone for 24 hours. For regular splashing or pooling, however, contact us first.

Can Si-COAT 579CM be used on pipelines?

Yes, on the outside of above ground pipelines and pipe racks. It handles UV, heat cycles and condensation on exposed pipework. However, it is not for buried or submerged pipe. For those, contact us and we will advise on a suitable system.

Can a corrosion maintenance coating prevent corrosion under insulation?

Corrosion under insulation happens when water gets behind lagging and sits against the steel, out of sight. Si-COAT 579CM’s flexibility suits the heating and cooling cycles on insulated pipework. However, CSL’s data sheet does not give a continuous service temperature or cover use under insulation. So for insulated lines, send us the operating temperature and we will confirm suitability with CSL.

How does Si-COAT 579CM handle extreme temperatures?

Silicone generally handles heat better than epoxy and polyurethane. CSL’s data sheets list the cured film’s temperature stability from minus 60°C to 200°C. In addition, 180% elongation lets the film move through large daily temperature swings without cracking. For application, however, the surface must be between 5°C and 60°C. For surfaces that run hot all the time, contact us and we will confirm the detail with CSL.

Does Si-COAT 579CM resist UV radiation?

Yes. It showed no degradation after 5,000 hours of accelerated weathering to ASTM G154. Its colour also changed by less than 1 delta E. In a separate 1,000 hour Suntest, it showed no discolouring or loss of gloss. That matters in Southern Africa, because strong UV breaks down organic topcoats fast.

What is the lifecycle cost advantage of a corrosion maintenance coating?

The savings come from the job itself and from fewer repeat jobs. First, you skip blasting, containment and two extra coats. Next, crews spend less time on scaffolding and the plant loses less production time. Finally, a longer life means fewer maintenance cycles over the life of the asset. Because every site differs, we work through the numbers with you per project.

What VOC content does Si-COAT 579CM have?

The TDS gives a VOC content of 290 g/L (2.42 lb per US gallon). It is a solvent based industrial coating. So in confined spaces, make sure of good ventilation or use respiratory protection, as the TDS and SDS require.

Which tests has Si-COAT 579CM passed?

On its own, it passed the 36 month Florida Fence Test with scribe and 3,000 hours of ASTM B117 salt fog. It also passed 5,000 hours of ASTM G154 UV weathering and ISO 2409 cross cut adhesion at Class 0. In addition, it passes direct impact, mandrel bend and high pressure water washing up to 150 bar. For rail use, it can achieve HL3 under EN 45545-2.

As a system with CSL 979 primer, it passed ISO 12944-6:2018 for C5 High and 2,500 hours of ASTM B117 salt spray.

Where is Si-COAT 579CM available?

CSL Silicones makes Si-COAT 579CM. Technical Solution Supplies distributes CSL Silicones products across Southern Africa, including the DRC and the Seychelles. We provide specifications, application guidance, samples and on site technical support. For more, see our industrial coatings page and our high voltage insulator coatings.

Who should I contact for a specification or quote?

Contact Technical Solution Supplies for project specific guidance, coating specifications and pricing.

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

Technical Articles:

Scroll to Top