When specifying products for fire protection applications, such as intumescent coatings used for structural steel fire protection, it’s important to ensure that the specified products are formulated for the particular operating environment.

Intumescent coatings are typically either waterborne or solvent borne; while waterborne intumescent coatings are traditionally formulated for use in dry, internal controlled environments, solvent borne intumescent coatings are generally suitable for use in both internal and external locations.

Any coating system’s durability will be tested when it is exposed externally to rain and UV. Therefore, incorrect specification of intumescent coatings for any particular exposure conditions can ultimately lead to severe degradation in their fire performance. This is most likely to occur when a waterborne intumescent coating has been applied in an external location. Even if the waterborne intumescent coating is specified with a top seal as a finish coat, it does not automatically qualify the system as being suitable for use in external environments.

Waterborne intumescent coatings are hygroscopic by nature, absorbing water from their surroundings. While the application of a top seal will act as a surface sealant initially, ageing and weathering can compromise the seal coat’s ability to prevent moisture intrusion, with surface degradation of the paint film even further accelerated by UV exposure. Once the top seal oxidises and micro-fine cracking occurs, moisture will penetrate into the intumescent coating and leach vital ingredients from the film, reducing its fire performance.

Moisture penetration also leads to visible swelling of the intumescent system, bubbling, and ultimately disbondment of the coating from the primer.

To protect the building owner and the occupants, the supplier/manufacturer of the intumescent coating system must provide qualified testing evidence that the coating system specified will be suitable for external application, for example, ETAG 018 part 2 exterior “X” classification. Nullifire SC902 has been tested in accordance with ETAG 018 durability classifications and meets all categories > X: exposed, Y: semi-exposed, Z1: humid internal and Z2: dry internal. In addition, it has been tested under “Prohesion” Cyclic Corrosion Test to ASTM G85:2009 Annex A5 – At 1000 hours total exposure in accordance with BS EN ISO 12944-6 test procedures for water condensation/ neutral salt spray.

Now more than ever before, the onus of responsibility rests with the specifier to provide the assurance that products specified for ‘life safety’ applications are indeed, fit for purpose.

Architecture & Design Team

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