Novel undercoats for use on porous bases such as, for example, concrete are disclosed. Said undercoats contain or comprise at least one epoxy resin, at least one latent hardener and at least one solvent. The above are characterize in being easy to produce, contain no isocyanate groups and form a good ageing-resistant adhesion, in particular, with single component isocyanate-free sealants, cross-linked by means of silane groups.