Masonry Magazine June 1978 Page. 16
TABLE 1
Insulation Material Properties
| Material | Density lb/ft (kg/m³) | Thermal Conductivity k Btu/h ft °F) (W mK) | Thermal Resistance R (per in.) °F(Btuhf (KWm) | Permeance, Perm-in. | Vapor Resistance fth (in. Hg) |
|---|---|---|---|---|---|
| Granular Fills: Vermiculite (Expanded) | 5-9 (80-144) | 0.44 (2.50) | 2.27 (0.40) | 62 | 0.0163 |
| Perlite (Expanded) | 5-8 (80-130) | 0.37 (2.10) | 2.70 (0.48) | N.A. | N.A. |
| Rigid Boards: Expanded Polystyrene, Extruded | 3.5 (56) | 0.19 (1.08) | 5.26 (0.92) | 1.2 | 0.8333 |
| Expanded Polystyrene, Molded Beads | 0.9-1.1 (14-18) | 0.28 (1.59) | 3.57 (0.63) | 2.0-5.8 | 0.5-0.1724 |
| Expanded Polyurethane, Extruded | 1.5 (24) | 0.16 (0.91) | 6.25 (1.10) | 0.4-1.6 | 2.5-0.625 |
| Perlite Aggregate | 11 (176) | 0.38 (2.16) | 2.63 (0.46) | 25 | 0.04 |
| Rigid Urethane | 2 (32) | 0.16 (0.91) | 6.25 (1.10) | 2 | 0.50 |
| Cellular Glass | 9 (144) | 0.35-0.44 (1.99-2.33) | 2.86-2.44 (0.50-0.41) | 0 | Very High |
| Preformed Fiberglass | 4-9 (64-144) | 0.21-0.26 (1.19-1.48) | 4.76-3.86 (0.84-0.68) | Very High | Very Low |
Tabulated values are from varied sources. Designers should check with manufacturers and other sources for more precise values. From 0 to 90°F (-18 to 32°C). Based on aged k-factor. N.A. Not available. Material thickness is 2.5 in.
Composition. Vermiculite is an inert, lightweight, granular insulating material manufactured by expanding an aluminum magnesium silicate mineral, which is a form of mica. The raw mineral is made up of approximately one million separate layers per inch, with a minute amount of water between each layer. When particles of the mineral are suddenly exposed to temperatures in the range of 1800°F to 2000°F (980°C to 1100°C) in a specially designed furnace, the water changes to steam, causing the vermiculite to expand into cellular granules of vermiculite insulation about 15 times their original size.
Perlite is a white, inert, lightweight, granular insulating material made from volcanic siliceous rock. When the crushed stone is heated to approximately 1800°F (980°C), it expands or pops much like popcorn as the combined water (2 to 6%) vaporizes and creates countless, tiny bubbles in the heat-softened, glassy particles. Perlite can be expanded up to 20 times its original volume.
Specifications. Specifications for water-repellent vermiculite and silicone-treated perlite are published by the Vermiculite Association and the Perlite Institute, Inc., respectively. Each of these specifications contains limits on density, grading, thermal conductivity, and water repellency; and the Perlite Institute's specification contains requirements limiting organic content (see Table 1).
Density-Water-repellent vermiculite density is specified at not less than 5 nor more than 9 lb/ft³ (80 to 144 kg/m³) dry loose weight. Silicone-treated perlite density is specified at not less than 5 nor more than 8 lb/ft³ (80 to 130 kg/m³) dry loose weight.
Thermal Conductivity The thermal conductivity, k, determined in accordance with the "Standard Method of Test for Thermal Conductivity of Materials by Means of the Guarded Hot Plate," ASTM Designation C 177, is specified for various mean temperatures.
Water Repellency-The primary purpose of cavity wall construction is to permit any moisture which may enter to drain readily from the wall. When materials which absorb water excessively are placed in the cavity, the cavity can no longer drain. As a result, the material will act as a vehicle by which moisture may be transmitted across the cavity to the interior wythe. The water repellency requirement is a result of experiments which indicated that untreated vermiculite and perlite material will accumulate considerable quan-