Aluminum magnesium silicate is constructed of approximately 1 million separate layers per inch, with a minute amount of water between each layer. Flakes of the mineral are placed in a furnace at 1800°F, which changes the water to steam, causing the vermiculite to expand to 15 times its original size. (The name originates from the vermicular, or wormlike, movement of the layers during expansion.) The expanded material is soft and pliable, silvery or gold in color, and contains less than 1 percent water by weight (Fig. 7.15).
Untreated vermiculite has an R-value of 2.3 per inch, compared with an R-value of 2.5 per inch for the treated material. Vermiculite is usually hand-installed, is nonabrasive, pours easily into irregular spaces, and is suitable for both horizontal and vertical applications. It is noncombustible, odorless, resistant to vermin, and nonirritating.
As discussed in Chap. 16, W. R. Grace Co., the manufacturer of Zonolite vermiculite loose-fill insulation, was hit with three class – action lawsuits after failing to warn the public that the Zonolite attic insulation it sold from 1963 through 1984 contained tremolite
Figure 7.15 Vermiculite. (Strong Lite Products Corp.)
asbestos. Grace discontinued its attic insulation in 1984 but still produces a loose-fill vermiculite masonry insulation. The U. S. Environmental Protection Agency (EPA) estimated in 1985 that 940,000 American homes contained or had contained Zonolite attic fill.22 Although it is not possible that all Zonolite installations were contaminated, more than 70 percent of the vermiculite ore mined in the world came from the Libby Montana mine, which has been closed since 1990. This particular mine was unusual because the area also included a natural deposit of tremolite asbestos.
If you know you have vermiculite insulation in your attic or walls and you are concerned about it, it probably makes sense to test the material to see if it contains asbestos. A trained consultant or licensed contractor should collect the sample and get it analyzed at a laboratory.