A cementitious product and method of modifying the properties of a low or medium density FRC product by providing a predetermined pore size distribution. The pore size distribution is obtained such that in critical zones of the distribution, the pore volume is substantially equivalent to or less than the pore volume in a respective critical zone of a conventional high density FRC product. The resultant material provides improved properties over conventional medium density FRC products, in particular improved freeze/thaw durability and/or improved workability.