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The importance of top coat compatibility with your fire rated steel

Jul 26, 2019

With its strength, flexibility, and high fire protection rating, structural steel has long been favoured by the traditional engineering, infrastructure, and construction industry.
In Australia, a number of passive fire protection materials are widely used. In the early days, cement and Vermiculite were the primary applications, however, with advances in technology, growing emphasis on aestethics and considerations to build times the application of intumescent paints on top of structural steel has grown.
This is predominantly due to the fact these coatings are aesthetically pleasing, and require only a thin application, making them cost-effective and more flexible in terms of design. As such intumescents are now becoming a top choice in building construction and maintenance.
In this blog, we will tackle passive fire protection doesn't stop at the intumescent paint alone, and how, through application of a compatible top-coat, you can achieve maximum compliance, within budget and on time. We will also explain the importance of using compatible top coats to ensure that the fire-resistant characteristic of intumescents will not be jeopardised. 

Challenges of structural steel

In the past, the protection of steel has been almost an afterthought. Whether it is from general traffic or fire, consideration as to how to prolong the structural integrity of the steel has been almost non-existent, or decisions made at the expense of other important factors. Taking care of it has become a low priority despite it being an indispensable foundation for any building.
Today, new structural steel members come with a prime coat, usually referred to as shop coat. This is the first layer of paint that was applied in the fabrication plant. However, its usefuleness is limited and insufficient especially as regards what could be termed Compliant steel fire protection.
Yes, painting structural steel might once have been more demanding compared to other materials in the construction site, but with the introduction of modern painting methods such as roller and spray painting, there is no longer an excuse to fail to protect steel be it for protection or aesthetics.

Coating for Fire Rating Steel Columns

A steel beam cross section showing the 4 coatings involved with intumescent fire protectionWe have already established early on that new members are coated with a primer before they are brought to the construction site. On-site, this surface should be reinforced with another layer and with a passive fire protection system in the form of intumescent paints. These paints are used in insulating the steel by forming a carbon layer or char in cases where temperatures exceed 120 degrees celcius.
Based on the requirements of the steel and where they are in the structure, protection is usually required to meet either 30, 60, 90, or 120 minutes.

In the modern building world where looks are everything, steel is often left exposed and painted to portray a raw look. However, what some in the building game fail to realise, is not all top coats are compatible with all thin-film intumescents

What are top coats really for?

Top coats are applied mainly for aesthetic purposes - as a decorative finish coat that gives structural steel a satin or glossy finish which meets the vision of the architects (and because intumescent finishes are matte in nature). However, top coats can also be utilised to provide an extra layer of protection to the intumescent paint system.

Compatibility of top coats with intumescent paints

Enhancing the appearance of structural steel may seem straightforward but it actually needs to follow certain guidelines. First off, the determination of what topcoat to use must be based on the environmental classification ISO 12944.

  • Solvent-based, single pack thin-film intumescents – May require topcoat in Internal C1 environments if steel needs resistance from abrasion or likely to be exposed to weather during construction.

    • For Internal C2 environments, topcoats are encouraged to ensure the long-term durability of the intumescent paint system. When it comes to External C2/C3/C4 environments, topcoats with external grade coating are required to cover the intumescent paint.

  • Water-based, single pack thin-film intumescents – The use of topcoats for this type of fire-rated paint for any environment, whether Internal C1, Internal C2, External C2/C3/C4, or C5 is not recommended or required.

  • Epoxy, two pack intumescents – Topcoats for this type of paint is not required unless the possibility of exposing structural steel to weather is high. This is applicable for all types of environments under ISO 12944.

It is important to tnote that in the application of top coats, the correct thickness should be considered to ensure that proper protection is provided and that the fire resistance quality of the intumescent is not affected. Not all manufactured paints are compatible with Nullifire coatigs, so it is essential you find out before applying it.

While there are various options that you can choose for top coating, you also need to consider if the intumescent is exposed to high UV radiation levels. If so, you have to choose a decorative paint with high UV resistance and high colour retention. Another consideration when selecting topcoats is the frequency of heavy cleaning or exposure to wash-down of the fire-rated steel.
If you are confused as to what type of topcoat to cover your intumescent-painted structural steel, always consult with the manufacturer of the intumescent paint. For Nullifire products, contact the team from Permax now.

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