A liquid flame retardant composition is in the form of an admixture which includes a phosphate-based flame retardant, ammonium hydroxide and zinc borate. The invention extends to a method of providing a phosphate-based liquid flame retardant composition, to the use of a phosphate-based flame retardant, ammonium hydroxide and a zinc borate in the manufacture of a liquid flame retardant composition, to a cellulosic material treated with the liquid flame retardant composition and to a method of inhibiting strength loss in a cellulosic material when the cellulosic material is exposed to heat.