Stone
Description
Stone used as a structural material can be of two main types; natural or cast stone and can be used for blockwork load bearing walls or non-load bearing walls, beams , lintels, columns or arches .
General considerations
Stone is generally considered to be non-combustible and will not contribute fuel to a fire but can undergo failure when affected by fire.
There are numerous types of stone used as structural material and each has individual properties. In general, stone is affected by thermal shock from firefighting activity after exposure to temperatures greater than 550°C but for most stone types this temperature is closer to 700°C.
Thermal shock, either by direct cooling by water or extinguishing the fire, can result in delamination or spalling of the stone. Stone containing quartz, e.g. sandstone and granite, will be weakened by fire and may crack or become friable (crumble or reduced to powder) at temperatures greater than 573°C.
Limestone will undergo calcination of calcium carbonate at temperatures above 600°C and this will rapidly increase beyond 800°C. Calcination will reduce the strength of the stone.
Cast stone is a special form of simulated stone, defined by the UK Cast Stone Association (UKCSA) as any product manufactured with aggregate and cementitious binder intended to resemble and be used in a similar way to natural stone. Cast stone is either homogenous throughout or consists of a facing and backing mix. It is used as an alternative to, and manufactured to resemble, natural stone. Cast stone will behave very similarly to concrete.
Cast stone is predominately used for facings and decoration but can also be used in structural beams or lintels particularly around doors and windows.
Inherent benefits
- Stone is non-combustible and will not contribute to fire size
- Generally natural stone is easily identified; a large proportion of historic buildings will have structural natural stone
Inherent hazards
- A very severe fire can result in structural collapse of stone structures
- Natural stone is affected by thermal shock and can delaminate or spall particularly when subjected to firefighting jets, leading to large sections of stone falling onto personnel below
- It may be difficult to differentiate between cast stone and natural stone; therefore the behaviour of concrete should also be considered
Further information
Effect of fire damage on natural stonework in buildings, BRE