Two new processes, a sealing and a decontamination process, are presented. The sealing is an elastic synthetic material based on a two-component polyurethane system. The material is sprayed without propellant, cures within a short time, and can easily be removed. By using the newly developed sealing process, many disadvantages, which had to be tolerated up to now, can be avoided. The sealing process has already been used in nuclear power plants in the Federal Republic of Germany. For chemical decontamination of surfaces a paste containing aggressive agents is applied. After some time, the paste is stripped from the surface as a film together wtih the contamination without aerosol formation or secondary contamination. With this decontamination process, it is possible to avoid the use of large quantities of acid and of rinsing water.