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Pumice-Crete is a low density and resource-efficient concrete consisting of pumice aggregate, Portland cement, and water. It is an economical alternative to conventional building methods and materials because it combines structural strength and insulation in one product. Besides the variety of design applications Pumice-Crete is a durable, fireproof, and noise-resistant material that can be used in a variety of climates.
Pumice is a lightweight volcanic, sponge like rock formed by expansion of gases while molten lava rapidly cooled. This glass froth is found in shallow deposits in New Mexico, Arizona, California, Oregon, Washington, and Idaho. Due to the material's inert nature it does not react with any ingredients of concrete or steel. With an average cured weight of under 50 lbs per cubic foot, Pumice-Crete produces a cured strength of 400 psi (compared to 2,000 psi in concrete) with an insulating value of R-1.5 per inch (compared to R-0.1 in concrete). Although over 350 residences have been completed in Colorado and New Mexico with Pumice-Crete, no official fire rating has been performed.
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One manufacturer estimates that the lightweight product has an estimated R-value of 1.5 per inch. However, the R-value has not be validated by laboratory testing.
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Pumice-crete is made from naturally-occurring volcanic rock.
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The durable product is resistant to moisture, fire, noise, and insects. It does not react with concrete or steel.
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In Western states pumice is available locally. In the East availability is difficult but improving as demand and familiarity with the product grows.
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No official fire rating has been performed.
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Pumice-Crete is mixed, either at a central plant and delivered in standard mixer trucks, or right on site with only enough cement to coat the aggregate and bind it. More cement increases the strength but reduces the thermal insulating qualities, whereas less cement increases the thermal insulating qualities but reduces the structural adequacy. For a single-story structure for example, an average mix proportion would be 2 to 2.5 bags of Portland cement for every cubic yard of Pumice-Crete with enough water to create an even paste around the aggregate.
Pumice-Crete is typically poured on top of a concrete footing or slab. The reusable forms can be lighter than for conventional concrete construction, usually consisting of 1/2" plywood with 2x4 frame backing at 2' spacing. Two-story construction walls are poured with a thickness of 14" to 16", requiring no additional insulation or structural reinforcement. Pumice-Crete can be reinforced to increase seismic and additional load resistance. According to contractors, Pumice-Crete domes spanning 30' and rising two stories can be poured with no interior support. Window and door openings are defined with 2x wood frames, which are more economical and lighter than typical concrete forms. Once forms are removed, after an average cure time of 3 days for a 16" wall, surfaces are plastered with two interior and two exterior coats, which improves thermal performance by trapping air within the honeycomb pumice-crete mix. Because of the uniform coarseness of the poured wall, plaster surfaces do not require stucco netting.
Different roof systems can be specified for Pumice-Crete walls. After the desired height of the wall is reached either a structural concrete bond beam is poured over the top where anchor bolts are provided to fasten to wood plates, or rebar can be extended from the bond beam for masonry roof systems.
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Pumice-crete is a environmental conscious, non manufactured building material. The resource-efficient, lightweight construction material does not require heavy form work. The material's structural and thermal properties can be achieved in one application, compared to drywall and stud construction, it can save labor and natural resources. The relatively large wall thickness allows room for surface detailing. The price is between $20 to $25 per ton.
Due to the fact that Pumice-Crete is still a new building material in most of the U.S., availability in some parts of the country may be difficult. Successfully mixing and detailing Pumice-Crete, requires experience. The 14" to 16" wall thickness reduces valuable floor area.
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