Fireproofing Resource Library

That Wonderful Volcanic Popcorn

By Charles Ballenger and Richard Dunlop

VOLCANIC LAVA from the wastelands, of western America is being popped like popcorn to produce a material that can slash construction costs, cut heating bills and increase fire protection. In some forms, the volcanic popcorn promises to increase the storage space in your refrigerator, help place cheaper meat and fruit on your table and perform hundreds of industrial tasks. It even provides Hollywood movie makers with realistic dandruff for actors.

This new pearl-gray material is called perlite in both its raw and processed forms. It is n glassy volcanic lava known to man for thousands of years, but it took a metallurgist working in a little Arizona town to discover its unusual properties.

Since the beginning of time, the lava flows in our western lands have existed in the badlands, in the mountains and the desert. The badlands are like a close-up view of the moon, forbidding and lonely. Men in their search for minerals passed them by.

Perlite itself is so razor-edged it will cut a hiker’s boots to ribbons. It is too brittle and sharp for roadbeds. It is no wonder’ that the rattlesnake and the Gila monster had the perlite barrens to themselves.

Now, however, perlite is a bonanza mineral. Expanding or popping perlite transforms it into a coase, lightweight aggregate. Combined with plaster, perlite aggregate is causing a basic change in the plastering industry, With cement it forms an extremely lightweight concrete which promises to save huge quantities of steel. Moreover, perlite is absolutely fireproof. It makes highly effective insulation and soundproofing.

Dr, Harry Huntzicker” director of research for United States Gypsum says: ” If. in the laboratory, we were to take natural elements and combine them into a perfect aggregate, we probably would end up with perlite.” ,

The processing of this perfect aggregate is almost an engineer’s dream in simplicity. No deep burrowing in the earth is necessary as perlite can be scooped up from the surface. After’ being crushed and graded, perlite is heated in furnaces at a temperature between 1400 and 2200 degrees Fahrenheit. Rapid parching explodes the grains of perlite into kernels which look something like tiny dried peas. Then the material is ready for use.

Easy as all this sounds, the process went undiscovered until 15 years ago when Lee Boyer happened upon it quite by accident. Boyer, who was operating an ·assay office

in Superior, Ariz., had taken an ancient assay furnace and converted it into an open-end firebox. For months he experimented with the furnace in the hope of fusing a mixture of silicates into a new insulating material for the telephone company.

One day he brought in a sack of crumbled perlite from the great lava flows on the slopes of near-by Picket Post mountain. Acting on a hunch, he threw a shovelful of the brittle stuff on the Acmes and peered into the furnace to see what would happen . Suddenly the perlite began to pop. The exploding particles bombarded the interior of the furnace and whizzed out on the feet. at his feet. He cut off the flames and stood watching with amazement until the popping stopped. Then he picked up ahandful of the expanded perlite and examined it curiously .

With a microscope Boyer could make out a cellular structure with sealed pores. He realized immediately that pelite would be remarkably resistant to the conduction of heat. Boyer then took raw and expanded perlite samples to the Arizona Department of Mineral Resources in Phoenix. There it was found that raw perlite contains f!’Om two to five percent of water sealed in the pores. When it is heated, the water changes in to s team and the perlite explodes. It is thought that this water was trapped when the erupted lava and accompanying s team

were cooled rapidly beneath the waters of a lake or stream. The department’s tests not only confirmed Boyer’s observation on insulating qualities of perlite, but revealed that perlite was absolutely fireproof, extremely lightweight and had many other valuable properties.

Back in Superior, Boyer set up a pilot plant for the production of perlite. While experimenting. he used the mineral as an aggregate with gypsum plaster in place of sand. To test it he plastered the office building and outdoor screen of a Phoenix drive-in theater. After 13 year s of exposure to the blazing Arizona sun and chilling desert nights, the plaster is as sound and uncracked as the day it was applied.

War shortages cut off further development and only now are the potentialities of perlite becoming evident, particularly in the building industry. Processing plants are springing up all over . Perlite is usually crushed and screened at the mine. It is then shipped, unpopped, to an expansion plant near the market. Huge freight savings are made because one carload of perlite blows up to 10 or more carloads of the finished product. In the most modem expansion plants, the substance is handled pneumatically from slart to finish.

The expansion of perlite was not a patentable principle and soon a host of independent producers were in the field. Today, nearly all the big gypsum processors have staked out their claims in the perlite industry and the race to market the new material is on in a big way.

The ultraconservative building industry always has been slow to accept new methods and materials, But perlite has met every requirement of the contractors, Builders and architects are employing perlite plaster and concrete in the construction of skyscrapers, apartments, warehouses, farm buildings

and especially private homes.

Pedite plaster can cut by at least 15 percent the amount of steel needed in a skyscraper, according to the architectural firm of Holabird & Root & Burgee. This amount of steel in a typical building is devoted to supporting masonry required to give the steel itself essential fireproofing, since steel has a relatively low melting point.

With light steel and light aggregate plaster, the architects found about 20 pounds per square ground foot could be saved in a typical 12-story building over the conventional steel frame fireproofed with concrete. This resulted in a 40-pel’cent saving in cost.

The lightweight steel frame went up faster with less labor, and greater flexibility of design was possible. The steel used in this technique is more plentiful than the steel in larger rolled beams commonly used.

Interior walls made with the perlite plaster weighed 12 pounds per square foot instead of 40 pounds. Perlite plaster and concrete used\ with aluminum building materials make the new 30-story Alcoa Building in Pitts burgh the lightest office building of its size ever built. Total weight of the building’s exterior walls was only 40 pounds per square foot as against about 150 pounds for conventional walls. A neighboring skyscraper with 6000 square feet less floor space used nearly twice as much stl’uctuJ”a1 steel. The greater fireproofing and insulating qualities of perlite plaster and concrete contributed to another saving in the Alcoa Building. The exterior wall of a typical office building has a four-inch facing and eight-inch backup wall. With perlite, a four inch backup wall provided the same insulation and adequate strength. This added the equivalent of a floor and a half of rentable space to the building. Space in a swanky office building doesn’t exactly rent for peppercorn, and Alcoa is reported to be quite happy about the added revenue, One of America’s biggest plastering contractors has found that because perlite plaster is only half as heavy as sand plaster, his men can, with less fatigue, put on 50 percent more perlite plaster by hand in a day.

Because of a new plastering machine developed for use with lightweight aggregates such as perlite, walls can be put up much faster.

Sand plaster and concrete are too heavy for the machine but, when perlite is the aggregate, the machine is able to blow the material onto the walls at such a clip that a workman can do four times as much wall area in a day as the fellow who is troweling sand plaster by hand, in a new 12-story Cleveland apartment project, builders were able to save 45 tons of steel by the use of perlite plaster on ceilings and for column fire protection, This amounted to a cash saving of more than $8000 in the 100-dwelling-unit structure, Perlite is processed and packaged under rigid quality controls at the plant. It is delivered to the building site in neat bags, For many jobs a premixed perlite and gypsum is available, All the plasterer has to do is add water. For special jobs, perlite and gypsum must be blended at the site, The bags of perlite are so lightweight that they can be stored on the floor where the work is being done. Because the materials are out of the weather, they do not have to be thawed before use. All of these advantages will help save you money when you set out to build or buy a home constructed with perlite.

Even the building methods are unusual. You go to see your new house. The walls are up and the building is ready for plastering. A truck pulls up, loaded with perlite and gypsum plaster packaged in neat, ready-la-use sacks. Also on the truck is an odd-looking contraption which turns out to be a plastering machine. Workmen run a long hose into the house, pour mixed plaster into the machine and add water. They spray on the plaster with such speed that you’re in your house weeks sooner than you expected.