Masonry Magazine October 1962 Page. 12
Insulating the cores of a block wall with vermiculite masonry fill.
What Is VERMICULITE
This month MASONRY brings to MCAA readers another article in the informational series of interest to the mason contractor. "What Is Vermiculite" was written by the Vermiculite Institute, Chicago, Illinois, at the request of MCAA editors.
Vermiculite is a mica-like mineral (a hydrated magnesium-aluminum-iron silicate) best known for its insulating properties. Other characteristics have made it useful in the chemical and agricultural industries. It was first described in 1824 by Thomas W. Webb, writing in the AMERICAN JOURNAL OF SCIENCE:
"If subjected to the flame of a blowpipe or that of a common lamp, it expands and shoots out into a variety of fanciful forms.. If this proves to be a new variety, would it not be better in giving it a distinctive appellation to select one that will indicate the peculiar property it possesses?. I term it vermiculite."
Vermiculite expands under heat because water molecules are contained within the mineral and between its paper-thin layers. When the ore is heated to around 2000° F., this water turns to steam, causing the layers to separate and move apart into accordion-shaped granules. The individual flake expands 10 to 12 times its original size, trapping thousands of dead air insulation cells. The color changes from dark gray to glistening gold. Additional insulation value comes from these shiny, golden surfaces, which reflect radiant heat as a mirror reflects light.
The main uses of vermiculite in construction are as fill insulation and as an aggregate in lightweight concrete and plaster, acoustical plaster, and fireproofing that is sprayed directly to structural steel.
One of the more unusual uses, which dramatizes the insulating and fireproof properties of expanded vermiculite, was related in a picture story several years ago by a popular national magazine under the title "Hottest Freight." A Canadian steel producer was shipping 65-ton white hot steel ingots by rail from an open hearth pit to a mill 180 miles away. At a temperature of 1800° F., the ingot was loaded onto a bed of vermiculite granules in a steel box, and quickly covered with two inches of vermiculite. Workmen were photographed walking around on this mere two-inch covering. The upper half of the box was then lowered in place. During the 22-hour rail trip, the temperature of the ingot dropped only. Undamaged, the vermiculite was retrieved and used to insulate other ingots. Shipping the ingots hot eliminated weeks of cooling and reheating.
A relatively recent development of interest to mason contractors is a vermiculite treated to provide water-repellent insulation for masonry walls. It is the result of ten years of research, and won approval from the brick and tile industry after almost a year of testing by the Structural Clay Products Research Foundation and Pennsylvania State University in co-operation with the Vermiculite Institute. The Foundation's standards for cavity wall insulation are much more rigid than for insulating materials fully protected from the weather. To obtain approval, the insulation must not permit water to be transmitted across the cavity. The insulation must be able to support its own weight in the cavity without settling; and, finally, must be an inorganic material or have comparable resistance to rot, termites, and fire.
A severe water permeability test was conducted at the Foundation's Research Center according to procedures developed by the National Bureau of Standards and described in BMS Report 82. A masonry cavity wall with a 2½-inch cavity filled with water-repellent vermiculite was built to leak at the rate of 2.6 quarts per hour. For six days (144 hours), 5½ to 8½ inches of rain was driven against this wall continuously by a 50-mph wind. Ninety-five gallons of water entered the cavity, but no water permeated across the space through the vermiculite during the entire test period.
When the vermiculite was removed, it was found to be reasonably dry to the touch. Adjacent to the mortar on the outside wythe was a thin layer of material 1/8 to ¼ inch thick, that appeared to be saturated. But analysis of the total moisture content of the insulation, including this saturated layer, showed less than 2 per cent of the total amount of water that had entered the cavity. The test had established that free water would not permeate across the cavity through vermiculite masonry fill.
MASONRY • October