The invention concerns a halogen-free flame retardant plastic composition, for coating a substrate, comprising an acrylic resin and an intumescent agent. It is in the form of plastisol, and comprises therefore a plasticizing medium wherein the acrylic resin and the intumescent agent are dispersed, said plastisol being formulated such that, in combination: the viscosity remains not more than 6000 mPa's, measured with a Brookfield RVT viscometer at 20 revolutions per minute, its rheological behavior is pseudo-plastic and Newtonian.