Insulation Alternatives: Sprayed Fiber Insulation Cellulose, fiberglass, or mineral wool sprayed in a moist state into an open stud cavity  Four entries in the PATH Technology Inventory describe alternatives to conventional fiberglass batts or roll for use in open vertical cavities:
- Non-fiberglass batts
- Sprayed foam insulation
- Sprayed fiber insulation
- Blown or Foamed through a membrane.
This document deals with sprayed fiber insulation. Cellulose, fiberglass, or mineral wool (rock wool and slag wool) is sprayed in a moist state into an open stud cavity. Moist cellulose creates its own glue, but some manufacturers add adhesive. Both mineral wool and fiberglass need added adhesive. After application, stud edges are scraped clean with a special milling tool made for that purpose. As long as the "salvaged" insulation is free of debris it can be sent back to a mixing machine for reuse. Properly installed, it completely fills the cavity, suppressing air leakage. Sprayed-on cellulose is a mature technology. The chief concern with its use is to carefully monitor the water content of the material, and to refrain from closing in the cavity until its moisture content has dropped to a stable level, typically around 10 percent. Cellulose is treated with borate fire-retardant for fire and vermin resistance. Fiberglass, sprayed on with some water and adhesive, can also be sprayed into wall cavities. Though having a slightly lower R-value than cellulose, it also fills the cavity and suppresses air movement. It is sprayed at 24% moisture content, but because the fiberglass does not absorb moisture, it dries quickly. Mineral wool (rock wool and slag wool) is sprayed into stud cavities with water and adhesive at between 10% and 20% moisture content. The material in place is a non-combustible fire-retardant, and can be used to create 1-hour and 2-hour walls. Many companies make more expensive products (with substantial amounts of adhesive binder) from cellulose, wood fibers, fiberglass, or mineral wool that can be spray-applied directly to almost any substrate. These products typically are used for acoustical or thermal insulation in commercial applications, where the material is left exposed (as in a hanger, warehouse or recording studio). At least one manufacturer of sprayed-on mineral wool markets a direct spray product, using Portland cement as a binder that can be applied to crawl space walls and left exposed. 
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Cellulose Insulation is covered by the following government and industry standards: - Consumer Products Safety Commission (CPSC) Standards: 16 CFR Part 1209 and 16 CFR Part 460;
- ASTM Standard C-739;
- ASTM Standard C-1149.
- The States of California and Minnesota have their own standards, based on the ASTM standards.
Fiberglass and Mineral Wool Insulation are covered by: - ASTM Standard C519, Test Method for Density of Fibrous Loose-Fill Building Insulations.
Fiberglass Insulation is rated under ASTM C1014-88 and ASTM C764; and - ASTM E136 - Noncombustible,
- ASTM E84 - Flame Spread Index of 25 or less; and Smoke Generation of 50 or less;
- ASTM C518 - Thermal Resistance;
- ASTM C665 - Rated Inorganic (does not promote fungus growth).
Mineral Blowing Wool is rated by ASTM C687, C764, E84 and E136. It is a fire-proofing material, and has zero flame spread and low or zero smoke generation.
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Material for open wall cavities is sprayed through an applicator hose with water added at the nozzle. Applied density for cellulose and mineral wool is typically 4.0 pcf, while lower-density fiberglass is applied at 2.0 to 2.5 pcf. Material is oversprayed; then a wide scraper tool is drawn along the studs or joists to clean off the excess. If this material is clean, it is put back into the hopper and re-used. Neither fiberglass nor mineral wool absorb water, so the water used for application (23% by weight for fiberglass, 17% by weight for mineral wool) can dry out in less than a day. Cellulose absorbs water, and so dries slowly. If the mix is applied too dry (to reduce drying time), it tends to fall out of the cavity; while if applied too wet, it may take too long to dry. Some installers apply the material with a minimum of water, then tack a netting over it to hold it in place (see "Blown In Fibers Through a Membrane Covering"). However, in humid conditions, especially in cool maritime climates, the material may never dry enough to cover it safely. Spraying into an overhead cavity is problematic because of the tendency for the material to fall out because of vibration, before a finish can be applied. Surface sprayed material can be sprayed directly against almost any clean substrate. Typically, the material cannot be left exposed where it can be reached, as it is not abrasion resistant. Products with a cementitious admixture are more durable than those with latex or other adhesive.
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Open cavity sprays can, if properly applied, completely fill the stud cavity, eliminating air circulation within the wall and providing a continuous air barrier. They also provide substantial acoustical protection. No membrane or netting is necessary to hold the product in place. Mineral wool provides excellent fire resistance and the highest acoustical rating of the three materials, and it also is totally inert. Borate treatment of cellulose provides it with fire protection and vermin resistance. Depending on the supplier and geographic regions, installed cost for in-cavity sprayed-on cellulose, fiberglass and mineral wool can be about 50% higher than a typical fiberglass batt installation. The cost of mineral wool varies with the distance from a source of minerals. Also, it is not typically stocked by the normal dealer network used by homebuilders. Installed cost for surface sprayed commercial products is typically higher than in-cavity sprays because they contain substantial amounts of adhesive binder. One brand of mineral wool fiber mixed with portland cement is marketed for use on crawl space walls, and on basement walls when covered by a wall finish. The material is commonly used exposed in overhead applications as acoustic and thermal insulation. Most materials will adhere overhead up to 3" in thickness. Surface sprays can also be aerated on discharge to reduce their density. | 
