Effective Steel Fireproofing: Intumescent Coating or Cementitious Coating?

30thMarch 2021

When you think of the damage fire does to a building, you probably think of the destruction of internal spaces. However, there is much more to consider than just what is visible to the eye. The steel and those elements holding the building up are elements which can mean the difference between life and death for occupants and those fighting the fire.
It means that consideration as to how to best protect the structural steel from fire is essential,  because once the steel reaches a certain heat, its structural integrity is compromised and there is an increased likelihood of building collapse.
With increased scrutiny to the role of building materials in controlling the spread of flame and protection of the building in the wake of several large fires it is essential that those responsible for the construction and maintenance of buildings take the correct steps to protect the steel of the structure. As with all things building, there are a wide range of fireproofing options available, albeit, there are two key options (if you exclude concrete encasement): intumescent coatings and cementitious coatings. While both are able to mitigate the effect of heat (In the short term) thereby limiting damage to structural steel, it is worthwhile understanding how they work and a little bit more about them so you can understand which one is superior.

What is a cementitious coating?

This type of material, also known as lightweight cementitious, is proven and has been one of the most trusted materials for more than a century. To make it, perlite, vermiculite, or other lightweight aggregates are combined in a heat-absorbing material such as Portland cement which is often enhanced through the use of other additives like foaming agents which are mixed through it.
Cementitious coating can be classified as low, medium, or high, based on its density. When used for fireproofing, it needs to be layered continuously in several levels.


  • Affordable raw materials are used to create it
  • Most suitable for dry environments
  • Strong resistance to high temperatures


  • More field work required and labour cost is higher since the coating needs to be applied in many layers successively
  • The weight of it can be significant adding cost to the project by way of increased steel requirements
  • Not ideal for places with high moisture levels as it can cause gaps between the substrate and the cementitious coating
  • Prone to spalling, cracking, or disintegration when exposed to vibrations and heavy impacts

What is intumescent coating for steel?

A popular passive fire protection material, an intumescent sealant or paint (such as Nullifire) is made of materials that swell as a result of heat exposure – a process of charring. This act of charring makes the paint expand in volume and decrease in density, slowing down the steel’s heating and staving off the threat of collapse before fire crews can get the blaze under control.
Application of intumescent paint is relatively easy for qualified applicators. In many cases a single pass can offer enough protection against the threat of a fire. However, as needed, additional coats can be added to increase the fire-resistant limit of the structure.


  • Easy for trained applicators to apply; a single layer can provide much-needed structural steel fire resistance
  • Low maintenance; comes with excellent bond strength even without a finish coat
  • Does not absorb moisture, thus preventing corrosion
  • Low labour cost
  • Low VOC profile (SC902 specifically)


  • Not ideal for facilities where there is a high risk of mechanical damage  to the surface coating as this can cause areas where the paint comes off
  • On first inspection the cost appears higher compared to cementitious coating, albeit this is not necessarily the case when all factors are considered

The Verdict

While cementitious coating is a reliable passive fire resistance technology, as an older technology it lacks many of the advantages (in terms of cost-effectiveness, level of fire protection, ease and flexibility in application, low overhead costs, and wide availability) of an intumescent coating when it comes to protecting structural steel from fire.
Here at Permax we offers both water-based and hybrid intumescent paints through our relationship with Nullifire. Learn more about these coatings and find out which works best for your facility by contacting our specialists now.


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