[en] A method is described for forming a cured mass of radioactive waste materials to render it suitable for transportation and/or disposal. The waste material is mixed with a liquid containing a setting agent consisting of an aqueous suspension of partially polymerized urea formaldehyde. The mixture is then placed in a container with two electrodes positioned at or near the free surface of the material, and the resistance between the electrodes is monitored. A proportionate amount of a curing agent capable of hardening the mixture to a free standing hardening mass is added, and the mixture is retained in the container until the resistance between the electrodes reached a maximum and declines slightly. The container with its solidified contents is then ready for burial