This article presents selected properties of mixtures produced from two types of fly ashes from one coal-fired power plant. Mixtures made of fly ashes from a conventional boiler without flue gas desulfurization products (10 01 02) and from a fluidized bed boiler with flue gas desulfurization products (10 01 82) are subjected to testing. The mixtures are prepared using mine water. The tested mixtures are characterized by a liquid consistency in terms of flowability in a range from 160 mm to 280 mm. The mixtures made of 10 01 82 ashes show twice as much water demand, shorter setting time, and higher strength than those made of 10 01 02 ashes, but, unfortunately, they have a much higher volume of excess water. Moreover, the mixtures of 10 01 82 ash do not undergo full slaking, in contrast to the mixtures of 10 01 02 ash (conventional boiler). The requirements of the PN-G 11011:1998 standard, relative to the discussed parameters, are met by the mixtures made on the basis of ash 10 01 82 originating from a fluidized bed boiler in terms of flowability of up to 240 mm. This is the ash type useable in sealing technology.