Masonry Magazine June 1978 Page. 19
Moisture Retention Test
The test consists of pouring 250 ml of water through 400 ml of the insulation to determine the quantities of moisture retained, either as a result of rain penetration or vapor condensation, to a point where thermal efficiency would be largely destroyed. The specifications limit the amount of water that may be retained by the insulation following the test.
Rigid Boards
Expanded or molded polystyrene, expanded polyurethane, rigid urethane, cellular glass, preformed fiberglass, and perlite board have all been used as rigid board insulation materials in cavity walls (see Table 1).
Composition. Rigid board insulations are many and varied. They can be classified chemically and physically.
Chemically, rigid board insulation is classified as organic or inorganic.
Organic insulations include the various vegetable-fiberboards and foamed plastics. Inorganic insulations include glass fibers, perlite board, cellular glass, and mineral fiberboard.
Physically, rigid board insulation is classified as cellular or fibrous.
Cellular insulation includes corkboard, foamed glass, synthetic rubber with gas-filled cells, and foamed plastics. The newest of these materials, foamed plastics, are polystyrenes and polyurethanes. Air, or other gas introduced into the material, expands the material by as much as 40 times. Cells are formed in various patterns-open (interconnected) or closed (unconnected). Most rigid urethane foams are expanded with one of the halogen gases, which, due to their extremely low thermal conductivity, give foamed urethane its high insulating value. Gradual air leakage into the cells replaces some of the original gas and eventually reduces the thermal insulating quality by about one-third, but it nonetheless remains extremely good.
Fibrous insulation materials include various fiberboards, which can be made of wood, cane, or vegetable fibers bonded with plastic binders. To make them moisture-resistant, they are sometimes impregnated with asphalt. Fibrous glass insulation consists of nonabsorbent fibers formed into boards with phenolic binders, and is surfaced with an asphalt-saturated, glass-fiber-reinforced organic material.
Properties. Water entrapped in insulation can destroy the thermal-insulating value of some insulation materials. Water vapor can flow wherever air can flow-between fibers, through interconnected open cells, or where a closed cell structure breaks down. Wherever water replaces air, the insulating value drops drastically since water's thermal conductivity exceeds that of air by 20 times.
Fibrous organic insulations are especially vulnerable to moisture damage. Free water will eventually damage any fibrous organic material or organic plastic binder. Fiberboard long exposed to moisture may warp or buckle and eventually decay. The expansion and contraction that accompany the changing moisture content may lead to problems.
Though less vulnerable to moisture, inorganic materials are not immune. Water penetrating into fiberglass insulation not only impairs the insulating value, but may also dissolve the binder. Foamed cellular glass will neither absorb water in its closed cells nor allow the passage of water vapor. But, with mean wall temperatures alternating above and below freezing temperatures, ice formation can break down the walls between open-surface cells and the interior closed cells. Repeated freeze-thaw cycles can progressively destroy the foamed glass, leaving a water-saturated gray-black dust. Foamed polystyrene cells may also break down under repeated freeze-thaw cycles.
Insulation made of cellulosic fibers swells with moisture absorption and contracts on drying as much as 0.2 to 0.5%, with changes in relative humidity from 50 to 90%. Under such humidity changes, a 4-ft (1.2 m) long cellulosic fiberboard could contract 4 in. (6 mm), thus opening a joint.
Under a 100°F (38°C) daily temperature drop, not uncommon within the air space of an insulated cavity wall, a 4 ft (1.2 m) length of polystyrene board will contract nearly 3/16 in. (4.8 mm). Foamed urethane with its thermal coefficient of 30 x 10 in./°F (1372 x 10-6 mm/K), poses nearly as grave a problem as does foamed polystyrene.
Due to the large number of types of insulation, and even larger number of manufacturers, Table 1 lists only a few representative values for k. R. etc. In some materials, an aged value is given. In all such cases, the aged value is the one which should be used in design. Individual manufacturers should be consulted before using specific design values. Individual manufacturers' literature should also be consulted regarding other properties of their materials.
Foams
Urea-formaldehyde based foams are among the newer types of insulation materials available for use in cavity walls. These low-density, resilient foam materials have the ability to flow into odd-shaped spaces: around wires, piping, etc. They could be advantageously used for remedial work in occupied buildings as well as in new construction.
NBS Technical Note 946, see reference 7, is a report of the findings of an NBS study of urea-formaldehyde based foams. The study discusses both the advantages and disadvantages of these materials. Most important among the disadvantages are: (1) some material and performance properties have not been determined, (2) for some properties the data in the literature are contradictory, (3) for some performance properties, there is insufficient data available from which performance may be adequately evaluated, and finally, (4) no widely accepted standards or specifications exist in the United