Thin film intumescent coating systems generally have three components: a primer, a basecoat (the part which reacts in the fire) and a sealer coat. The basecoat usually comprises the following ingredients:
- A catalyst which decomposes to produce a mineral acid such as phosphoric acid.
A carbonific such as starch which combines with the mineral acid to form a carbonaceous char.
A binder or resin which softens at a predetermined temperature.
A spumific agent which decomposes together with the melting of the binder, to liberate large volumes of non-flammable gases. These gases include carbon dioxide, ammonia and water vapour. The production of these gases causes the carbonaceous char to swell or foam and expand to provide an insulating layer many times the original coating thickness.
They are mainly used in buildings where the fire resistance requirements are 30, 60 and 90 minutes. In recent years, a number of products have been developed which can provide 120 minutes fire resistance . They can be applied either on-site or off-site. In general, most on-site application is carried out using water based materials. However, where the structure to which the material is applied is not to have an end use in a dry, heated (C1) environment, solvent based materials are commonly used. Solvent based materials also tend to be able to cover a wider range of section factors than water based materials and can be used on-site to protect smaller sections requiring high thicknesses.
Both solvent based and water based coatings can be used to achieve attractive surface finishes. If a decorative or bespoke finish is required, this should be included in the specification. Thin film intumescents have the added advantages that they can easily cover complex shapes and post-protection service installation is relatively simple.
Typical expansion ratios are about 50:1, i.e. a 1mm thick coating will expand to about 50mm when affected by fire.
Detailed guidance on the specification and installation of site applied, thin film intumescent coatings is available from the Association for Specialist Fire Protection.