How preparation impacts performance

They say art is very subjective. What one person likes is not necessarily what someone else will.
Yet one thing that artists, critics and pundits alike agree on, is the selection of materials used becomes irrelevant if the preparation and surface used is not up to scratch.
This is true too of painting and coatings in construction and Fire Rating. When it comes to fire rating, there is one core truth which overrides all else. If you fail to prepare the surface, the fireproof coating will not work to the level desired or required.
Through this article we thought we would point out a few things you should to consider prior to the application of any timber or steel fire rating coating:

  • Size of steel section
  • Location of structural element to protect (timber or steel) and the impact of weather on the selection
  • Application Temperature (city vs country or winter vs summer)
  • Preparation of the surface (Primers, rust etc)
  • On-site vs of-site application and damage to some products in transport

What exactly is an intumescent coating system

An intumescent coating is defined as a coating system which can be applied to steel or timber for the purposes of increasing its resistance to heat stress during a fire. By acting as a fire retardant and an insulator it works to passively preserve the structure for as long as possible allowing fire crews to combat the flames and occupants to get out safely. When we talk about intumescents at Permax we refer to thin-film intumescents – a paint like coating which will swell to several times its original size in the case of fire. A thin film intumescent coating system is usually  composed of a primer, intumescent coating, and the topcoat.


The first coat of the system is called a primer. In the case of steel, it prepares the steel member for the application of the intumescent paint as it offers good adhesion of the latter to the substrate. Furthermore, the primer helps protect steel from corrosion, which if overlooked has potential to cause structural issues into the future.
When choosing a primer, it is important to take note of surface preparation, the method of application, as well as the condition of the steel and the drying requirements of the primer given the environmental conditions. If using a Nullifire product such as SC803, make sure you use the primer recommended by Nullifire.


Intumescent coating

There are different types of intumescent paints that you can choose from: water-borne, epoxy, or solvent-based. And then to make it even more exciting, there are coatings suited to cellulosic fires and others to hydro-carbon fires. What you select should be largely dependent on the size of the sections to be protected, the fire resistance period, critical steel temperature, and the fuel which will predominantly burn. These we will discuss in detail later.



The topcoat is applied on the surface of the steel, on top of the intumescent coating. It can be used mainly to improve aesthetic value or to protect the member from decay and other environmental challenges.
When choosing a topcoat, it is important to ensure that such will not restrict the fire-protection quality of the intumescent coating.  If you are unsure, ask before applying. If using Nullifire, ask us for a recommendation on which manufacturers to select from.


Other factors to be considered prior to application

When identifying the ideal intumescent coating for steel, there are a range of important factors that you should consider.


Fire resistance period

In Australia, the typical fire resistance period extends between 30 – 120 minutes. Depending on the location of the member to be protected, the size of the steel, the environment and other factors, the NCC will provide the requirements for the FRL required. If you need help with this, ask our team, we have experts on staff trained in optimizing steel designs to achieve optimal outcomes.


When applying the intumescent paint, you need to take particular attention of the Atmospheric corrosivity zones, provided for in AS 4312. For instance, for C1 and C2 environments, no primer is needed.
The relative humidity for the application of intumescent paint should be less than 95%. Ergo, when working in industrial and marine vicinities as well as areas with high humidity think about the product you are applying and if it is appropriate for use. Relative humidity and a steel surface temperature of structural steel to external weathering should also be taken note of.

Application temperature

First and foremost, the steel surface should be at least 3°C above the dew point. But beyond this, check the ambient temperature before application and check the recommendations from the manufacturer, as the temperature at application can affect product performance.

Size of steel section

The steel section size will dictate the thickness of the intumescent paint. The steel section factor has to be calculated to identify the thickness that will help achieve the given Fire Resistance Level or FRL. You can learn more about this on our blog entitled The Role of Steel Sections on the use of Intumescents.

The intumescent coating process

Before applying the primer, the steel member needs to be adequately prepared first in accordance to the standards imposed by the CPCCPD3033A (Apply intumescent coatings) training of the Australian Government Department of Employment, Skills, Small and Family Business.


Preparing the steel surface

Prepare the steel by treating it via abrasive blasting in accordance with the with Australian Standards 1627.4 (Part 4: Abrasive blast cleaning).

According to AS 1627, “Abrasive blast cleaning utilizes a stream of abrasive particles directed onto a metal surface to remove rust, process scales and foreign particles. The abrasive may be propelled by centrifugal force, or carried in an air or water stream, or both.”

This process should only be done by a licenced professional or one that has undergone appropriate training.

Once the substrate is clean and ready, the area should be set up to be conducive for the application of the primer, and then the intumescent coating. The equipment used should also be checked to ensure that the application is sprayed in uniform thickness.
Ensure that when applying the material that all areas are coated equally, including hard-to-reach areas like welds and corners.

Applying intumescent paint on steel

When the steel surface has been blasted or galvanised steel de-oiled and the primer applied, the steel member is now ready for the application of intumescent coating either via a roller, a brush, or an airless spray. Regardless of the method used, the applicator must ensure that the temperature and humidity requirements for application are maintained. On top of that, the wet film thickness must be regularly monitored per the manufacturer’s data sheet. Once the coating is dried, the dry film thickness should be measured allowing you to determine if the fire resistance period required will be achieved.

The process of applying intumescent coating to timber is relatively similar. Nevertheless, ensure that the wood is completely stripped of any pre-existing finish to prepare for application of water-based intumescent coating suitable for timber.

On-site or off-site application of intumescent coating

The application of an intumescent coating system can be done on-site or off-site — both of which possess their own benefits.


On-site application. As the name suggest, this is done on the building site, after the steelwork has been erected. As you don’t need to transport the steel, there is little need to worry about handling damage or installation adjustments.
Nevertheless, on-site applications can slow project progress as there is a need to minimise complimentary trades on-site and there may be application delays caused by unpredictable weather.
Off-site application. In this solution, the application of the intumescent system is done in a controlled environment where there is sufficient lighting and the pollutants are restricted. Generally, this is a dedicated warehouse where the environment can be managed. Because no one else is in the space, you need to worry less about damaging other assets in the vicinity nor about contributing to the health and safety risks of other tradies.
Once on site, the steel can be erected and other trades can work as per normal, thus improving timelines. However, there is a slight increase in transportation cost as there is a need for more careful handling (even though Nullifire’s range of intumescents are extremely hard wearing).

Consult Permax for your Passive Fire Protection Needs

For a highly-effective passive fire protection system, consult with an expert team who covers the planning, preparation, application, and maintenance of intumescent coating like Nullifire. We know our stuff and we would love to help you, give us a call and speak to one of our specialists now.
After all, what use is it designing a beautiful building if it won’t stand the test of time.

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You are about to download a file from the Permax site. Please note All technical advisory notes generated by Permax are based on research papers, indicative fire tests and any other existing evidence. These documents should not be used as an official evidence as design engineers should review the information and determine the reliability of the documents.

Permax constantly update the documentations based on the new fire testing outcomes and change of standards and regulations. To ensure the documents you read are up-to-date, please contact the Permax technical team.