Compositions containing an alkali swelling polymer and a pH buffer with a pH between 3 and 7 may be used to treat a wellbore. The pH buffer prevents the swelling of the alkali swellable polymer. The compositions may be placed in the wellbore, whereupon they contact another material with pH increasing properties. The pH of the compositions increases, causing the compositions to swell and form a seal. The alkali swelling polymer may be an alkali swelling latex.