PURPOSE: To provide a hardener compsn. for water glass which consists of aluminum sulfate, sulfuric acid and water, remains in a stable state for a long period and forms no precipitate under vibration and agitation nor undergoes phase separation.

CONSTITUTION: The hardener compsn. is prepared by dissolving 2W4g (in terms of Al2O3) of aluminum sulfate and 7W45g of sulfuric acid in water to make a total of 100cc. An aqueous solution of water glass is mixed with a hardener solution obtained by diluting the above hardener compsn. with water, so that the resultant grout may contain 6W11g of SiO2, 0.14W0.2g (in terms of Al2O3) of aluminum sulfate and 1.4W1.6g of sulfuric acid.

EFFECT: The hardener compsn. remains stable over a long period and makes control of the gel time easy. There is 2 wide tolerance for variation in the amount of the hardener added to water glass and a solidified product with high bonding strength is obtained.

USE: Fortification of soft ground and checking of water.