Masonry Magazine February 1966 Page. 16
Three stages of perlite processing shown above illustrate the increase in volume after furnacing. The same weight of perlite (one ounce) in each photo.
WHAT IS PERLITE?
As far apart as masonry walls and rocket fuels are in function, they do have one requirement in common. They must be insulated to perform efficiently.
Perlite a specific type of siliceous volcanic glass once thought to be a worthless rock provides the insulating needs for both rocket fuels and masonry walls. When heated at high temperatures perlite expands and turns white. Its white color is one of its most distinguishing features.
The expansion characteristics of crude perlite were discovered by an assayer in Superior, Arizona in 1941 while investigating perlite for use in enamel. Further investigations and commercial development were delayed until after World War II.
In 1949, the year the Perlite Institute was founded, 71, 000 short tons of crude perlite were sold or used by U.S. producers. This figure increased to over 380,000 short tons in 1965 and indicates the rapid and continuing growth of the perlite industry.
MINING AND PROCESSING
Perlite ore is quarried from open pits by conventional power equipment. Although it is found in several mountainous western state, 80 percent of all output comes from New Mexico.
The crude rock is crushed, ground, dried, and graded into various particle sizes required for particular uses. It is shipped in bulk to expanding plants located throughout the United States and Canada.
At the expanding plant, the ore is stored in bins or silos. It is injected into either a horizontal or vertical type furnace at a temperature between 1600° and 2100°F, to produce the expanded perlite aggregate.
When perlite ore is heated above 1600°F, a small amount of trapped water contained within the volcanic glass vaporizes and converts the heat softened glass into foam. The foamed particles solidify, and the countless macroscopic air cells created in each particle account fo perlite's excellent thermal insulation and light weight.
Expanded perlite can be commercially produced in density range from 3 to 20 lbs. per cubic foot, dependir upon gradation and anticipated use. There are ASTM specifications for plaster aggregate, concrete aggrega and loose fill insulation.
SILICONE TREATED PERLITE
Of particular interest to masonry contractors is the recent development of a silicone treated, water-repellent perlite loose fill to insulate concrete blocks and masonry cavity walls. Demand for lower heating and cooling costs in recent years has created a need for insulating masonry walls. This demand for greater insulating efficiency arises pirmarily from the growing use of air conditioning and electric heating to improve comfort.
The insulating performance of loose fill perlite has been clearly established by laboratory tests and field applications. It is the most widely used insulating fill material for the handling and storage of rocket fuels and liquified gases. These liquids must be kept at temperatures as low at -200°C. The same basic design requirements for the application insulating efficiency, economy, ease of installation, and free-flowing ability to fill any shape-apply equally to masonry wall insulation.
In masonry wall construction building professionals quickly recognized a cavity wall insulating material must be able to maintain its insulating value should moisture actually penetrate the walls. The insulation must not permit water to be transmitted across the cavity.
To improve the water-repellency of perlite loose fill insulation, Perlite Institute encouraged research and sponsored tests to develop suitable, non-flammable silicone for treating perlite. It was determined that silicones improve the water repellent properties of perlite by 50 percent or more and that they can be applied economically to perlite.