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Slate is a fine-grained, foliated, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade, regional metamorphism.
Because it is quite impermeable, and so dry, it does not get broken by tree roots. It is typically found at 750mm down below a layer of yellow clay. Yellow, found on the surface, absorbs water quite readily so becomes very soft in the winter. The two different types make quite different bricks.
Slate has been quarried in north Wales for almost two millennia with the Segontium Roman fort at Caernarfon being roofed by local slate in the late second century. Export of slate has been carried out for several centuries, which was recently confirmed by the discovery in the Menai Strait of the wreck of a 16th-century wooden ship carrying finished slates.
The ability of stamped concrete to resemble other building materials makes stamped concrete a less expensive alternative to using those other authentic materials such as stone, slate or brick. [7] There are three procedures used in modern stamped concrete which distinguish it from other concrete procedures: the addition of a base color, the ...
Accrington bricks, or Nori, [1] are a type of iron-hard engineering brick, produced in Altham near Accrington, Lancashire, England from 1887 to 2008 and again from 2015. [2] They were famed for their strength, and were used for the foundations of the Blackpool Tower and the Empire State Building .
Stronger and less porous engineering bricks (UK Class A) are usually blue due to the higher firing temperature [3] whilst class B bricks are usually red. Class A bricks have a strength of 125 N/mm 2 (18,100 lb f /sq in) and water absorption of less than 4.5%; Class B bricks have a strength greater than 75 N/mm 2 (10,900 lb f /sq in) and water ...
Reemtsma cigarette factory in Hamburg by Fritz Höger A piece of vitrified brick. Clinker bricks are partially-vitrified bricks used in the construction of buildings.. Clinker bricks are produced when wet clay bricks are exposed to excessive heat during the firing process, sintering the surface of the brick and forming a shiny, dark-colored coating.
Two adjacent vermiculated blocks showing rather different interpretations of the pattern. The most common variation of rustication is the smooth-faced, where the external face of the block is smooth, as in ashlar, and differs from that only by the cutting in at the joints; this became increasingly popular, and is now the most commonly seen type.