Montmorillonite occurs mainly in bentonite. The minerals in montmorillonite not only absorb water on the surface, but also within its mineral structure. It has a capacity to absorb large amounts of water and swells up to twenty times in volume. This absorption occurs quickly, and when the surroundings dry out again the clay releases its moisture. It is, therefore, useful as an absorbent waterproof membrane on foundation walls made of brick and concrete. Bentonite clay can be purchased in panel form, packed between two sheets of corrugated cardboard: the clay is approximately 0.5 cm thick and the cardboard gradually rots away intentionally. The panels should be under a certain pressure, which can be achieved by a compressed layer of earth of at least 0.4 m.
There is an abundance of montmorillonite clay, but in very few places, so high levels of transport energy are needed. Like all mined substances, large mines cause local environmental damage. Apart from this the environmental problems of the product are of no consequence.
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