Extenders are chalky products and are used for a large variety of reasons.
It is often erroneously thought that paints that contain extenders are always of a lesser quality. On the one hand extenders are used to make less expensive paints and the pigment is partially replaced resulting in paint with a lesser tinting strength. But on the other hand, it may be necessary to use an extender; some pigments have such a tinting strength that it is impossible to work with a paint that contains only pigment. Other desired properties, too, can be negatively affected without the addition of an extender. In general, we can say that extenders are essential in many cases in order to obtain a paint that is easy to work with, and that they do not adversely affect the durability of the paint layer or can even improve it.