Perlite is a natural glass of volcanic origin mined by open cast methods in parts of the world such as Iceland, Greece, Hungary and the Czech Republic. It is pulverized and expanded in rotating kilns at about 9001200 °C, which increases its volume between five and twenty times. Expanded perlite was first produced in the USA in 1953. It has the consistency of small popcorn and is used as an aggregate in mortars, plasters and lightweight concrete blocks. It is also used as loose fill for the thermal insulation of buildings, insulating refrigerating rooms and high temperature insulation. It has soundproofing properties similar to those of rockwool.
Using perlite as an aggregate in plasters and mortars provides a substantial increase in the thermal insulation of a wall. For example, 15 mm perlite plaster is the equivalent of a whole brick wall thickness or 240 mm concrete. Perlite can also be added to earth constructions to improve insulation properties.
Because perlite absorbs some moisture it runs the risk of a reduced insulation value; or an increased settling problem within a conventional wall construction when the material is used as a loose fill. To avoid this, a moisture repellent is often added to the mix before it is poured into the wall. This can be a natural resin. However, the most common method is to mix in silicone (less than 0.5% by weight) and heat it to 400 °C, Hyperlite. Bitumen can also be used.
When perlite is exposed to even higher temperatures naturally, it expands and becomes a porous and monolithic rock called pumice. The pores in this stone are not connected, so the material does not absorb any water. Building blocks of crushed pumice in cement have almost the same properties as when light expanded clay aggregate is used.
Perlite reserves are large. Pumice occurs naturally and in large quantities in Iceland. Both are extracted by open cast mining with the environmental disturbance which that entails. A pollution risk of perlite is that it can cause irritation by exposure to its dust. The use of bitumen and silicone additives brings in the issue of oil extraction and refining. This can also include exposure to toxic substances in the production workplace. Pure and silicone-treated perlite has no side effects once installed in a building. Depending on how the bituminous products are incorporated, small emissions of aromatic hydrocarbons may occur.
As a waste product, bituminous perlite must be disposed of at special depots. Pure perlite is inert. The siliconized material is also considered inert. Re-use is possible by vacuuming the loose material out of the structure.
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