Method of making a cementitious product

A method of manufacturing a porous cementitious product, which method comprises in the following order:

• (a) forming a cementitious premix including sand as aggregate by mixing premix components with water;
• (b) mixing the cementitious premix formed in (a) with a heat-activated gas-generating agent and then immediately casting the premix in a desired configuration in a formwork, wherein the premix is sufficiently viscous to achieve gas bubble retention but not so highly viscous so as to inhibit formation and migration of gas bubbles, and wherein the formwork is underfilled by from 30 to 50% based on the volume of the formwork;
• (c) allowing gas bubbles to be generated within the premix by reaction involving the heat-activated gas-generating agent thereby causing the premix to expand in the formwork;
• (d) collapsing the expanding premix at its upper surface by contacting with a formwork lid or by subjecting the upper surface to trowelling, screeding and/or rolling;
• and
• (e) curing the premix,
• wherein gas bubbles are generated and/or collapsed at specific locations within the premix in order to produce a porosity profile along a cross-section of the product such that the product comprises a relatively low density core region and higher density outer regions.