Eleven hardening slurries were prepd. by wet mixing bentonite (40-60 g), blast furnace slag (195-475 g) and lignite fly ash (15-175 g) and studied for d., viscosity, H2O sepn. by sedimentation, structural strength, hydraulic permeability, thermal behaviour, microstructure and phase compn. during the hardening. The slurry contg. only a small amt. of the fly ash and a large amt. of bentonite showed the best properties and was recommended for construction of cut-off walls.