The present invention relates to a sealing compound for coating a substrate, which is a mixture of a predominantly uncured base mass and a curing agent containing at least one epoxy composition, wherein the base mass contains a mercapto-terminated base polymer based on polyether, polythioether, polythioethersulfide, polysulfide, copolymers thereof and/or mixtures thereof, wherein the base mass, the curing agent or both contain at least one photoinitiator based on a sterically hindered nitrogen-containing organic base, and, through the effects of high-energy actinic radiation, the at least one photoinitiator dissociates at least one radical per molecule based on a nitrogen-containing organic base, from which a nitrogen-containing organic base having a pKa value of the conjugated acid in the region of 6 to 30 is formed, which acts as an active catalyst for the curing of the base mass. The present invention also relates to a corresponding method for coating a substrate with a sealing compound.