Masonry Magazine June 1979 Page. 26
Silicone Repels Water from Masonry Wall Insulation
Expanded perlite masonry wall insulation is rapidly increasing in popularity as the cost of energy rises. The free-flowing, glassy, bead-like material is ideal for filling the hollow cores of concrete block walls and also the space between inner and outer cavity-type walls. Displacing air in these spaces with perlite can cut heat losses by as much as 50 percent.
To assure that perlite insulation maintains its good insulating characteristics for the life of the wall, manufacturers throughout the country, licensed by GREFCO, Inc., to produce and market perlite under the trade name Permalite, treat the material with a silicone emulsion to prevent water adsorption (as opposed to absorption). By silicone treatment of the perlite, water penetrating the wall is rejected by the insulation and protected from heat transmission or damage to interior walls.
From Mined Rock
Perlite is formed from a glass-like volcanic rock of the obsidian family mined in the Rocky Mountain states. The rock contains about 3 to 5 percent water in hydrate form. When the rock is crushed into fine particles and heated to temperatures above 1,600 F, the mineral softens, the water vaporizes, and the particles expand with explosive force. The reaction is similar to making popcorn.
Expanded perlite loose-fill insulation is opaque white and has a density of from 5 to 8 pounds per cubic foot (pcf), compared to the 70 pcf of the crushed rock. Expansion creates countless cells in the glassy particles, which accounts for the material's low thermal conductivity. Expanded perlite has an insulation "R" rating of 2.7 to 3.1 per one-inch thickness, depending on density.
Perlite's inorganic composition is a major advantage. The insulation is not affected by extremes of temperature, will not compact after application, will not burn or rot, is rodent and insect proof, and is easy and safe to handle and install. It is an effective insulation for masonry walls because it can be simply poured into concrete block cores or double-wall cavities.
Water Adsorption Intolerable
Although perlite is inorganic, it can adsorb relatively large quantities of water because of the extremely large surface area present within each expanded particle. Water adsorption cannot be tolerated because water degrades the insulation's thermal characteristics. Further, in cavity walls, the adsorbed water may eventually work its way across the insulation to wet interior walls. Water typically seeps into masonry walls through small cracks. Wind-driven rainfall is particularly troublesome.
Silicone Stops Adsorption
Application of a small amount of Dow Corning 347 silicone emulsion to the perlite after expansion and while it is still hot drastically cuts water adsorption. Water that does seep through a wall immediately flows down through the silicone-treated perlite to the base of the wall where it can be carried away by weep holes. Very little of the water is retained by the insulation, and almost no chance exists for the water to work its way across the insulation and penetrate through to interior surfaces.
Extensive laboratory tests by the Perlite Institute on a cavity wall with 2½-inch perlite-filled interwall spacing with built-in leaks subjected to simulated 50 mph winds and 5-inch per hour rainfall, showed no wetting of the interior wall or compaction of the perlite.
Other tests by the Institute have demonstrated that the moisture repelling characteristics imparted by the silicone
Water repellency test at Silbrico Corp., Hodgkins, III., starts with two 2-diameter, 12"-long open plastic tubes with screening in the bottom ends containing 400 ml (about 7.7) of perlite loose-fill insulation. The tube on the left holds untreated perlite; the tube on the right the silicone-treated material. Beneath each tube is an empty plastic beaker. The graduate contains 250 ml of red-dyed water.
In the water repellency test, the dyed water is poured into the tube containing the treated perlite. Note that the water is running through the material and into the beaker. Shortly before this photo was taken, another 250 mi of red water had been poured into the left tube. The untreated perlite within adsorbed all of the water: none even dripped into the beaker at any time during the test.
During the test a 3-minute lapse indicates that the water dripping into the right beaker from the silicone-treated perlite has stopped.
At the end of the water repellency test by Silbrico Corp., a producer of Permalite perlite, all but about 6 ml of dyed water was recovered after the beaker under the silicone-treated perlite was emptied back into the graduate. Perlite Institute standards require that the treated material retain no more than 75 ml of the water.