In years modified bentonites have also been used as filling material instead of conventional calcite in developed countries. The degree of whiteness of the bentonites to be used in this sector should be over ISO 85, have high swelling feature and its free bulk density should be 0.2 – 0.3 kg/l.
In order that the bentonites can be used in this sector, it should be calcined gradually at 200°C in size of 1 – 4 mm, should comprise min. 80% montmorillionite, and it should have min. 10% absorbtion feature with 20% relative humidity. And the maximum humidity in its structure should be 2%.