Method of producing a building element

A method of manufacturing a cellulose fibre reinforced, high impact strength carbonate building element which comprises steps of:

• (a) mixing solids and water to produce a slurry in which the solids consist essentially of at least one alkali earth oxide or hydroxide and an amount of cellulose fibres in the range 7-40% by weight of solids;
• (b) forming the slurry as a gas permeable shape having voids that contain water and so that the shape has a porosity in the range 35 to 50%, where porosity is the volume of the voids within the shape expressed as a percentage of the volume of the whole shape;
• and
• (c) causing carbon dioxide gas to permeate into the shape by means of the voids thereby converting the hydroxide(s) to carbonate(s) and imparting high impact strength to the resulting element, this converting step being performed in a short time period dependent on the percentage carbon dioxide present in the processing atmosphere to produce a building element of high impact strength which is not dependent on the presence of aggregate for its impact strength, said period being about 30 minutes for 100 percent carbon dioxide.