FD20 is a fire-resistance rating indicating a door or material can withstand fire for a minimum of twenty minutes. Meeting this standard requires coatings specifically tested and certified for the intended substrate and door assembly, not generic fire-retardant paints.

The primary alternative coating type is intumescent paint or varnish. These coatings expand when exposed to heat, forming a thick insulating char layer that slows fire spread and protects the underlying timber [1]. Water-based intumescent paints are widely available in various finishes (matt and gloss), offering aesthetic flexibility while maintaining fire protection. Clear intumescent varnishes are ideal when the natural wood grain must remain visible; these typically require both a base coat for fire protection and a manufacturer-specified topcoat to protect the intumescent layer from moisture and wear [2].

Manufacturers offering FD20-tested intumescent systems include Envirograf, No-Burn, FlameOFF, and ProTek [3][4][5][2]. However, not every fire-retardant product qualifies: a coating that only reduces flame spread is insufficient for FD20 compliance. Epoxy-based fire-retardant coatings exist for timber in some industrial settings, though intumescent systems remain the standard approach.

Critical requirements for compliance: the coating must be tested to BS 476 Part 22 or EN 1364-1 standards; application must strictly follow the manufacturer's technical data sheet regarding spread rates and coat thickness; and the product must come with a certificate of compliance or declaration of performance specific to the substrate and door construction. Wood thickness significantly impacts overall fire rating, so certification must match the intended application.