lf one regards the filler’s only function to reduce the cost of the paint formulation, one will try to use as much of it as possible. Quite often one wants to replace some of the expensive, but very strong white pigment in light coloured paints by fillers such as calcium carbonate, aluminium silicates of magnesium silicates.
If quality is a major requirement however, the filler concentration will not be more than 30 %. Things are rather different if the filler is incorporated in order to improve properties, for example to impart good sanding down properties to primers. In such cases one can use much higher concentrations -indeed the amount of filler added may well exceed that of the pigment which, in primers, plays a subordinate role anyway.