Grey Bricks are a product of the brick making process and specific base material. In this case fly ash or specifically, class C and/or class F fly ash. This fly ash and water blend are then compressed at 28 megapascal pressure units for a full day and exposed to a steam bath of 150.8 degrees Fahrenheit. When this task is complete, the bricks are a light to medium grey in color.
These bricks are unique in that are more fire insulation than clay bricks; are a higher strength product, can better resist exposure to freeze thaw cycles, and are more consistent in size making it easier to create better joints with plaster. With these bricks they do not need to be soaked before proceeding with masonry construction.
For those who like brick construction techniques but don’t like the look of clay/red bricks, grey is always an option to consider.