The present invention relates to a heat-curable composition comprising at least one epoxy monomer comprising two or three epoxy groups, which is not a hydrolysis-polymerizable silicon compound, at least one epoxy compound bearing at least one silicon atom having at least one hydrolyzable group directly linked to the silicon atom and at least one epoxy group, and at least one epoxy ring-opening catalyst. The composition comprises at least 50% by weight of compounds having at least one epoxy group, relative to the total weight of polymerizable compounds present in the composition and provides upon pre-curing a tack-free coating that can be removed by treatment with a solution of sodium hydroxide, and upon post-curing a coating that cannot be removed by treatment with a solution of sodium hydroxide.