The results of gas pressure measurements in intergranular spaces of fast-setting sands hardened by active gaseous factor are presented in the paper. The research stand and the measuring methodology are described. Investigations concern the determination and recording gas pressure changes in the core sand along the hardened core, in three measuring points. The hardening gas was introduced both in a continuous and impulse way (gas-pause) at a constant pressure. The determined pressure changes of the active gas, which takes part in the chemical reaction of the hardening process, are compared with pressure changes of the neutral gas. The influence of the impulse way of a gas dosage on the core sand strength properties is presented as well as methods of limiting the active gas consumption are shown.