Abstract: Aluminum polyphosphate is made. To this end, solid aluminum hydroxide and polyphosphoric acid which are used in proportions corresponding to an Al:P molar ratio of 1:2.5 to 1:3.5, are introduced separately from, but concurrently with, one another into a reaction zone kept at 150.degree. to 200.degree. C. A moist friable consistency of the starting materials is maintained in the reaction zone by continuously mixing, kneading and comminuting them over substantially the entire period during which they are introduced into the reaction zone. The reaction is continued until a dry sandy powder is formed; and the powder is annealed at 400.degree. to 600.degree. C. over a period sufficient to yield a product undergoing a 0.5 to 1% weight loss on ignition.

Abstract: Hardeners of condensed aluminum phosphates for use in water-glass cementing compositions and process for making them. The hardeners consist substantially of a short chain aluminum polyphosphate with a chain length of 3 to 6 and a long chain aluminum polyphosphate with a chain length or more than 40. Quick-setting hardeners contain a high proportion of the short chain component and slow-setting hardeners contain a high porportion of the long chain component.