Abstract: The invention relates to aqueous solutions of alkali silicates and alkali hydrogen phosphates comprising:From about 4 to 18%, by weight, of K.sub.2 Ofrom about 2 to 11%, by weight, of Na.sub.2 Ofrom about 3 to 10%, by weight, of P.sub.2 O.sub.5from about 12 to 21%, by weight, of SiO.sub.2based on the sum total of the constituents including water, wherein the ratio of the sum totals of the parts by weight, of (K.sub.2 O+Na.sub.2 O):(P.sub.2 O.sub.5 +SiO.sub.2) is from about 1:0.9 to about 1:1.7 and has a solids content of from about 30 to about 50%, by weight. The solutions are homogeneous and stable and are particularly useful in improving the burning properties of organic/inorganic plastics. The invention also relates to a process for preparing these solutions which preferably involves introducing an aqueous alkali hydrogen phosphate solution into an aqueous silicate solution.