What Does C5 Very High Mean?

Posted on: 04/04/2025

In the ISO 12944 standard, which defines corrosion protection for steel structures using protective paint systems, the C5 Very High (C5-VH) classification refers to the most severe atmospheric corrosion environments – C5 – with the demand for a long durability – Very High / VH – of the coating system.

C5 – Definition

This classification applies to extreme conditions characterized by high humidity, frequent condensation, and severe pollution levels.

C5 environments include:

  • Industrial areas with high humidity and aggressive atmospheres, such as chemical plants and coastal industrial zones.
  • Coastal regions with high salinity, where structures are frequently exposed to salt spray.
  • The inside of buildings and factories with almost constant condensation or heavy pollution.

Durability Classes

The ISO 12944 standard also defines durability categories, which indicate the expected lifespan of a coating before requiring major maintenance:

  •           Low (L): up to 7 years
  •           Medium (M): 7-15 years
  •           High (H): 15-25 years
  •           Very High (VH): More than 25 years

A C5-VH system is designed for exceptional durability, capable of lasting over 25 years before requiring significant maintenance.

A Tougher Testing Standard for C5 Very High

The revised ISO 12944:2018 introduces a new, more demanding test regime (Test Regime 2). This method is significantly tougher than previous C5 High testing and includes a 2688-hour (112-day) cyclic aging test.

During this period, test panels are subjected to a continuous cycle of extreme conditions:

  •           72 hours in a QUV test cabinet (ISO 16474-3 A1) to simulate UV exposure.
  •           72 hours in a Salt Spray test (ISO 9227 5.2 NSS) to replicate marine and industrial atmospheres.
  •           24 hours at -20°C ± 2°C to test resistance to low temperatures.

At the end of the testing period, panels are assessed based on their degradation (ISO 4628-2, -3, -4, -5). Corrosion in the scribe and adhesion values (pull-off test) are measured as well.

When the tested panels meet the standard's requirements, it means that the paint system can be recommended for these environments and lifespan.

The revised ISO 12944:2018 introduces a new, more demanding test regime (Test Regime 2). This method is significantly tougher than previous C5 High testing and includes a 2688-hour (112-day) cyclic aging test.

During this period, test panels are subjected to a continuous cycle of extreme conditions:

  •           72 hours in a QUV test cabinet (ISO 16474-3 A1) to simulate UV exposure.
  •           72 hours in a Salt Spray test (ISO 9227 5.2 NSS) to replicate marine and industrial atmospheres.
  •           24 hours at -20°C ± 2°C to test resistance to low temperatures.

At the end of the testing period, panels are assessed based on their degradation (ISO 4628-2, -3, -4, -5). Corrosion in the scribe and adhesion values (pull-off test) are measured as well.

When the tested panels meet the standard's requirements, it means that the paint system can be recommended for these environments and lifespan.

What are the coating system with RD-Monoguard?

ClassificationCoating system – minimum dry film thicknessMNOC – Minimum number of layers
C5 Very High270 µ / 11 mils3
C5 High / C4 Very High200 µ / 8 mils2
C4 High / C3 Very High150 µ / 6 mils2
C3 High110 µ / 4,5 mils2

Life expectancy of the system before major maintenance: Very High: above 25 years / High : between 15 and 25 years

Real-world experience

Successfully passing these tests is a major milestone, reinforcing confidence in the system’s performance. However, in our industry, real-world experience remains just as crucial and even more.

RD Coatings: Proven Performance, Decades of Innovation

RD Coatings has been at the forefront of high-performance waterborne coatings for over 25 years. In 2016, RD-Monoguard was already a breakthrough innovation, becoming later on the first of its kind to obtain an official C5 High certification under ISO 12944. At that time, the C5 VH classification did not yet exist.

Since its launch, RD-Monoguard has been protecting major infrastructures worldwide—from Europe to North America, the Middle East, Africa, and Asia—thanks to the dedication of the RD Coatings network and forward-thinking customers willing to embrace innovative technology.

A growing number of private and governmental organizations are now choosing RD-Monoguard for its cost-effectiveness, user-friendly application, and environmentally responsible formulation, ensuring long-lasting protection for their steel infrastructure.

Additionally, RD-Monoguard is fully compatible with other RD Coatings products, allowing for tailored solutions that meet the specific needs of each project.

VERS. RDA-ISN-250404