6 October 2022 · By Geoff Wilkinson

Geoff Wilkinson offers key pointers to specifying fire-protective finishes

In June, Collaborative Reporting for Safer Structures UK (CROSS-UK) published a report on the use of intumescent coatings, which indicated that lessons have still not been learnt from evidence given at the Grenfell Inquiry. The report related to detailing and advice provided by manufacturers, which incorrectly advised that the coating would still be effective if it were applied to steel and then closely covered, leaving no gap for the expansion of the intumescent material.

An intumescent coating is intended to protect the substrate material – typically steel – from being adversely affected by combustion temperatures. In simple terms, intumescent coatings char and swell upon exposure to high temperatures when a fire occurs. The charred coating then acts as an insulating layer to slow the heat transfer to the substrate.

It follows that, for an intumescent coating to work, it needs space to expand when heated in order to form that protective layer. If designed incorrectly, a steel section’s temperature, and therefore its ability to carry a load, can be compromised.

The report raised the concern that architects may not be aware of the need to allow for expansion and that manufacturers and suppliers are still making misleading claims about their products. In a case examined in the report, the architect asked the correct question, but the supplier wrongly advised that (a) the steels will start to intumesce at 70°C and be fully active at 120°C, and (b) there is no scientific evidence to suggest a space between the steels and a covering is relevant.

Firstly, it is the coating and not the steel that will intumesce, but, that aside, the advice that there is no need to allow for expansion is simply wrong.

This brings up a much wider issue about the lack of understanding of intumescent coatings which are increasingly being seen in small projects as well as larger projects where fire engineers are likely to be employed, who should be aware of the need for correct detailing. Indeed we are now seeing intumescent coatings becoming almost the default solution in loft conversions and even used as an architectural feature in ‘exposed’ steelwork in domestic extensions.

The key pointers to successful specification and use of intumescent finishes are:

Intumescent products should not be seen as a simple note to add to the plan and architects on projects of all sizes should consider their design responsibilities under the new Building Safety Act and not rely on manufacturers claims or leave specification to the builder.

With the need to provide more detailed information as part of the post-Grenfell ‘golden thread’ recommendations, the use of intumescent products (indeed any products) for fire safety needs to be carefully considered, fully detailed and correctly recorded. Failure to do so, as we saw at Grenfell, can have tragic consequences.

I would recommend that you always check the test certificate for the product (not just the manufacturer’s sales literature) and also check out the British Constructional Steelwork Association (BCSA) guide to Fire Protection of Steel.

Geoff Wilkinson is managing director of approved inspectors Wilkinson Construction Consultants. www.thebuildinginspector.org

Tags Building Regulations fire protection intumescent coatings

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