Intumescent Fire Protection for Commercial Buildings: What Specifiers Need to Know

Intumescent coatings can provide structural steel with a clean painted appearance while forming part of a tested passive fire-protection system. Their performance depends on more than the product name: the building design, steel members, required fire resistance, primer, exposure and application records all matter.

Begin with the fire strategy

The required performance should come from the project's fire strategy and structural design. It should be confirmed by the fire engineer, structural engineer or other responsible designer rather than inferred by the coating contractor.

In England, the current Approved Document B is an important source of statutory guidance, but it is not a substitute for a project-specific design. The applicable guidance may also vary across UK nations and according to the project's approval route and date.

Define the steelwork accurately

A useful tender package identifies the steel members requiring protection and provides enough information to determine the coating build for the selected system. This normally includes section sizes, member references, exposure on three or four sides, section factors and the relevant design temperature.

Section factor describes the relationship between the heated perimeter and the cross-sectional area of a steel member. Slender members generally heat more quickly than stockier members, so the required protection can differ even where the fire-resistance period is the same. SteelConstruction.info explains section factors and their role in structural fire design.

Specify a complete tested system

The primer, intumescent layer and topcoat should be treated as one compatible system. The specification should identify:

• The selected intumescent product or the performance criteria for an approved alternative
• The product's relevant test and assessment evidence
• The approved loading or thickness data for the steel members involved
• The compatible primer and its permitted condition and thickness range
• The topcoat, where required, and its compatibility with the intumescent layer
• The environment or exposure category for the completed steelwork

Substituting one component can affect the evidence for the whole system. Proposed changes should therefore be checked with the responsible designer and coating manufacturer before work proceeds.

Include application and quality requirements

The specification should set out the preparation standard, permitted application conditions, coat sequence, inspection stages and acceptance criteria. It should also define who is responsible for checking the existing substrate and any shop-applied primer.

The required dry film thickness is not a standard figure that applies across the building. It should be taken from the selected manufacturer's data for the project-specific member, design and required performance.

The inspection plan may call for environmental readings, batch records, wet-film checks, dry-film measurements, repair records and photographs. The precise record set should be agreed before tender or mobilisation so it is included in the programme and price.

Plan for access and sequencing

Commercial projects also need practical coordination. Access, masking, ventilation, adjacent trades, curing time, weather exposure and the timing of primer or topcoat work can all affect delivery. Connections, difficult details and areas concealed by later work should be identified early.

Clarify responsibilities

The fire engineer and design team are responsible for defining the required performance. The coating manufacturer supports product-specific selection and loading information. The applicator delivers the preparation and application work against the approved documents. The contract should make these responsibilities explicit rather than leaving gaps between parties.

Newlook Protective Coatings can review the application requirements and quote for on-site preparation and intumescent coating once the project-specific design and coating system have been supplied or approved. Newlook does not provide the fire-engineering design or replace manufacturer approval.

The Association for Specialist Fire Protection technical library includes recognised guidance for specifying, installing and inspecting structural steel fire-protection systems.

To discuss a defined commercial project, visit Newlook's Intumescent Coatings service.