Abstract: An antifoulant coating composition and preparation method in which the final composition is composed of two Components A and B mixed immediately before the composition is applied, and usually an inert filler introduced at least in part via Component A. The active ingredient of Component A is a base formed of coal-tar pitch or equivalent and epoxy resin. The active ingredients of Component B are a curing agent for the epoxy resin and a solid organotin toxicant. Component B may be either a slurry of needle-like crystals of toxicant, or the toxicant may be dissolved in a suitable solvent. In the latter case the toxicant precipitates as needle-like crystals when Components A and B are mixed. The invention produces a composition of a viscosity which makes it easy to apply.