A process for the confinement of generally harmful solid materials is disclosed and claimed. The solid materials are immobilized and confined within a solid matrix for an unlimited storage free from pollution risks. The solid materials are mixed with at least one low condensed, liquid phenolic resin and a cross-linking agent which is selected from partly or wholly sulfonated linear and/or cyclic phenolic oligomers, and the cross-linking which forms said solid matrix under hardening is allowed to occur. When a mould is used for the hardening reaction, solid blocks are formed which are resistant to water, heat, and environmental acids and bases. These blocks need not be stored in a safe environment but can further be used for applications such as construction elements.