Intumescent Coatings

Thin-film intumescent coatings, typically 1 or 2 mm in thickness, offer fire protection to structural steel without noticeable visual effect. In the event of fire, the thin coating expands up to 50 times to form a layer of insulating foam. The carbonaceous material in the coating, typically starch, is charred, whilst the heat also causes the release of acids. These act to produce large volumes of non-inflammable gases which blow up the charring starch within the softened binder into an insulating cellular carbon layer. Coatings may be applied to give 30, 60 or 120 minutes' fire protection. Intumescent emulsion paints or clear varnishes are appropriate for use on timber, although where timber has been factory-impregnated with a flame-retardant salt, the compatibility of the intumescent coating and flame retardant must be verified.

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