The present invention relates to a pulverulent polymer post-crosslinked on the surface and absorbing water or aqueous liquids, synthesised from polymerised, optionally pre-crosslinked monomers containing partially neutralised carboxyl groups. The present invention also relates to a process for the post-treatment of the aforementioned polymers and the use of a solution of at least one salt of an at least trivalent cation for restoring the gel permeability of the aforementioned polymers that have been damaged by mechanical action.