Type A, especially type 4A zeolites are well adapted as detergent builders, said zeolites comprising (i) primary particles having a mean particle diameter ranging from 0.1 to 10.mu., (ii) a cation exchange capacity in excess of about 100 mg CaCO.sub.3 /g of anhydrous material, and (iii) a rate constant, relative to the surface area of the zeolite per liter of wash solution, in excess of about 0.15 s.sup.-1 lm.sup.-2. The builders are prepared by first determining the value of the rate constant for a given zeolite sample. Since a higher rate constant value corresponds to a lower degree of salt incrustation on fabrics, only those zeolites having a value above the predetermined minimum will be incorporated into detergents. Thus, zeolites otherwise appearing identical can be differentiated, with only those not causing high levels of incrustation being selected.