Novel cementitious containers for storage of hazardous waste are disclosed having an inner layer of substantially unhydrated cement in contact with the hazardous waste and an outer layer of hydrated cement. Cementitious hazardous waste containers may be prepared by compressing powdered hydraulic cement around solid hazardous waste materials and then hydrating an outer layer of the powdered hydraulic cement. An inner layer of powdered hydraulic cement remains unhydrated and capable of reacting with any water which might breach the outer layer or originate with the hazardous waste itself. The inner layer of powdered hydraulic cement is also capable of reacting with any carbon dioxide or carbon monoxide generated by decomposition of organic waste materials.