The viscosity increase of aqueous calcium carbonate pigment suspensions having high concentrations of dry substance is prevented by adding as a compatibility, dispersing, and/or grinding agent to an aqueous calcium carbonate suspension a copolymer of the formula: ##STR1## wherein R.sub.1 is H or methyl, R.sub.2 and R.sub.3 is H, C.sub.1-4 alkyl or a carboxylic acid group, R.sub.4 is H or C.sub.1-4 alkyl, R.sub.5 is a bridging group, R.sub.6 is H, a cation, an amino group, C.sub.1-3 alkyl, C.sub.1-4 ester or substituted amide and R.sub.7 to R.sub.9 each is hydrogen, a carboxylic acid containing group; K has a value between 30 and 65% by weight relative to the total weight; L has a value between 20 and 60% by weight relative to the total weight; M has a value between 10 and 45% by weight relative to the total weight; and the sum of L and M is equal to at least 35% by weight relative to the total weight, thereby preventing the shock effect when a concentrated alkaline electrolyte is added to the suspension.