Several types of compounds, with different performance capabilities, are used.  Builders have a number of functions, principally inactivation of water hardness.  This is accomplished either by sequestration, i.e. holding hardness minerals in solution, by precipitation, or by ion exchange.  Complex phosphates are common sequestering builders.  Sodium carbonate is a precipitating builder.  Sodium aluminosilicate is an ion exchange builder.  Other functions of builders are to supply alkalinity to assist cleaning, especially of acid soils, to provide buffering so that alkalinity is maintained at an effective level, to aid in keeping removed soil from redepositing during washing, and to emulsify oily and greasy soils.