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Lime plaster is type of plaster composed of hydrated lime (slaked lime), sand and water. Lime plaster is similar to Lime mortar, the main difference is based on use rather than composition. Traditional lime plaster also contains horse hair for reinforcement.
Improvement in the slow curing time of lime plaster, especially in cold and/or wet conditions was done in Roman times by adding volcanic ash (activated aluminium silicates) to produce hydraulic lime and hydraulic cement.
Today, cheaper power station fly ash or other waste products are used to make hydraulic lime plaster or cement instead of volcanic ash.
Lime plaster is sold as 'bagged' powder or hydrated lime; or is available as lime putty. Lime putty is generally considered to be more suitable for pure lime application.
Non-hydraulic lime is the most commonly used and known lime, also called (high) calcium lime or air lime, as it sets only by reaction with CO2 in the air and will not set until dry. This causes limitations in construction use as the lime can remain soft for months or years. Non-hydraulic lime can only set through carbonatation (re-absorption of CO2).
Hydraulic lime and hydrated lime must not be confused. Hydrated lime is merely a form in which lime can be supplied (as opposed to quicklime or lime putty); while 'hydraulic' refers to its ability to set under water, or in wet conditions.
Lime is an extremely caustic material when wet, with a pH of 12. (Lime when carbonated can be up to pH 8.6). As such, the use of protective goggles, gloves, and clothing is necessary when working with lime. Clean water should also be kept readily accessible for first aid purposes when working with lime in case of accidental eye or skin exposure.
- First aid for cases of skin exposure to lime involves neutralization with very mild acid such as vinegar or lemon juice.
- First aid for cases of accidental eye exposure consists of repeatedly flushing the eye for several minutes with fresh water. Medical attention should be sought in such cases.
Historical use in the arts
One of the earliest examples of lime plaster dates back to the end of the eighth millennium BC. Three statues were discovered in a buried pit at 'Ain Ghazal in Jordan that were sculpted with lime plaster over armatures of reeds and twine. They were made in the pre-pottery neolithic period, around 7200 BC. The fact that these sculptures have lasted so long is a testament to the durability of lime plaster.
Historical uses in building
- Lime plaster was found to have been a multi-purpose material at the archaeological site of 'Ain Ghazal in modern day Jordan. The site dates human occupation from 7200BCE to 5000BCE. Lime plaster is believed to have coated internal walls of buildings and to have been used as the main component of some anthropomorphical figurines discovered at the site.
- Some of the earliest known examples of lime use for building purposes are in early Egyptian buildings (primarily monuments). Some of these examples in the chambers of the pyramids, which date back to around 2000 B.C., are still hard and intact.
- Archaeological digs carried out on the island of Malta have shown that in places like Tarxien and Hagar, lime stucco was also used as a binder to hold stone together as well as for decoration at sites dating back as far as 3000-2500 B.C.
- At el-Amarna, a large pavement on brick was discovered that dates back to 1400 B.C. It was apparently the floor of part of the harem of King Amenhotep IV.
- Ancient Chinese used Suk-wui (the Chinese word for slaked lime) in the construction of The Great Wall of China.
- Ancient romans used hydraulic lime (added volcanic ash, an activated aluminium silicate) to ensure hardening of plaster and concrete in cold or wet conditions.
- The Aztec Empire and other Mesoamerican civilizations used lime plaster to pave streets in their cities. It was also used to coat the walls and floors of buildings.
- This material was used in the San Luis Mission architecture.
- Hagsten, Ellen. General Guidelines for Working with Lime Mortar and Limewash, Traditional & Sustainable Building, March 2007
- "Lime plaster statues". britishmuseum.org. British Museum. Retrieved 21 November 2013.
- J.N. Tubb, Canaanites, London, The British Museum Press, 1998
- Cowper, Ad. Lime and Lime Mortars, first published for the Building Research Station by HM Stationery Office, London, 1927
- ISBN 978-0-500-28714-9
Cedar Rose Guelberth and Dan Chiras, The Natural Plaster Book: earth, lime and gypsum plasters for natural homes'
J.N. Tubb, Canaanites, London, The British Museum Press, 1998
Stafford Holmes, Michael Wingate, Building With Lime: A Practical Introduction, Intermediate Technology Publications Ltd,