Fiber cement building materials with low density additives

A method of forming a low density building material, comprising:

• mixing a fiber cement formulation comprising hydraulic binder, ground silica, cellulose fibers, volcanic ash with water to create a slurry, wherein the cellulose fibers comprise greater than about 4% by weight of the fiber cement formulation;
• processing the slurry into a green shaped article;
• curing the green shaped article to form the low density building material;
• and
• wherein the volcanic ash is added in a quantity sufficient to lower the density of the building material to about 1.2 g/cm3 or less and maintain the moisture expansion of the material at a level of about 0.17% or less.

A building material formulation used to form a building product, comprising:

• a hydraulic binder;
• ground silica;
• cellulose fibers, wherein the cellulose fibers comprise greater than about 4% of the formulation by weight;
• and
• hollow ceramic microspheres, wherein the hollow ceramic microspheres are incorporated into the formulation, in a quantity sufficient to lower the density of the building material to about 1.2 g/cm3 or less, and wherein the hollow ceramic microspheres maintain the moisture expansion of the building material at a level of between about 0.13%-0.2%.

A method of forming a low density building material, comprising:

• mixing a fiber cement formulation comprising hydraulic binder, ground silica, cellulose fibers, hollow ceramic microspheres with water to create a slurry;
• processing the slurry into a green shaped article;
• and
• curing the green shaped article to form the low density building material, the building material having a density of about 1.2 g/cm 3 or less, wherein the hollow ceramic microspheres maintain the moisture expansion of the material at a level of between about 0.13%-0.2%, and wherein the cellulose fibers comprise greater than about 4% by weight of the total weight of the fiber cement formulation.