The invention relates to alkaline cleaners containing two components A and B, component A being a strongly alkaline solution comprising mostly alkali metal hydroxides and employed in an excess, component B being a concentrate comprising an aqueous silicic acid dispersion containing anionic, nonionic or amphoteric tensides, builder substances, stabilizers and optionally inorganic mineral acids, complexing agents and/or preservatives. Component B contains, as an active ingredient, adjusted to a pH in the range of from 1 to 11, a silicic acid dispersion obtained in situ by treating an alkali metal silicate solution with a mineral acid or a gas reacting acidically in aqueous solution. The dispersions also contain stabilizers, tensides and builder substances. If desired, additional agents conventionally contained in cleaning concentrates may also be added. The invention also relates to processes for preparing such cleaners by treating an alkali metal silicate solution with a mineral acid or a gas reacting acidically in aqueous solution and adding tensides, stabilizers and builder substances thereto.