Fiber cement building materials with low density additives

The invention claims a cement to the cellulose fibre reinforced construction material in the low density of volcanic ash additive the hollow ceramic tiny ball or the volcanic ash ball body and the combination of low density or other additive formulation. This prescription has the advantages of with the existing fibre cement product has light weight and low density at the same time does not increase the normal of the fibre cement mixture of lightweight inorganic material adding the relative humidity of expanding degraded and freeze-thaw. Said low density of the additive also gives material improved thermal stability of shape.