Building with Papercrete
Another advantage of papercrete is its relatively low cost. According to papercrete researcher Gordon Solberg, the total cost of materials for a house can be as low as $5 per square foot ($54 per square meter) if other sustainable strategies are applied such as installing used windows and doors.
Building from Ground Up
A typical recipe for papercrete consists of water added to equal parts of portland cement and repulped paper fiber, which can come from newsprint, cardboard, or even junk mail. The ingredients must be thoroughly pulverized and blended in a mixer.
Mike McCain, one of papercrete's promoters, has invented an ingeniously simple "tow mixer." The mixing blades of this da Vinci-esque machine are powered by pulling a trailer behind an automobile so that, as in a conventional concrete truck, the material is mixed by the time it reaches its destination.
"One of papercrete's amazing features is that it is extremely dimensionally stable even when wet," says green home builder Kelly Hart. "I have embedded glass directly into the material without any cracking or breaking over time." Stucco, by contrast, has a sufficiently different coefficient of expansion from glass that this kind of installation would be impossible.
Papercrete will hold fasteners such as screws (but not nails) and has a compressive strength of up to 300 pounds per square inch (21 kilograms per square centimeter).
Inspired by the pointed-dome trulli buildings of the Puglia region of southern Italy, Hart builds houses out of stacked "earth bags," which are polypropylene rice sacks filled with crushed volcanic rock. He then applies papercrete as a thick plaster on the earth bags on both the interior and exterior.
Because a principal ingredient is paper, papercrete reacts to moisture literally like a paper towel. In dry climates or in situations where it can dry out readily, it will not deteriorate. But much like wood construction with extended contact with the ground or long term dampness, there is a danger of mold and rot.
However, Hart's domes expose papercrete to rain, and no leaks or significant signs of wear have appeared in their five-year life even though the material absorbs a great deal of water.
A drawback to papercrete's status as a green material is the use of portland cement which gives off greenhouse gases in curing and contains substantial embodied energy. Substituting adobe clay for cement is one option for a more sustainable approach.
Tests of so-called "fidobe" (fibrous adobe) have shown it to be durable even in wet conditions. Its principal difficulty is an extremely long drying time, and all papercrete products are somewhat delicate until completely cured. Adding sand or other minerals to the mix is a way of making it harder and more impervious to water.
Because papercrete is still experimental, building codes don't have official provisions for regulating it. But there are several instances in which papercrete has been given experimental status by building officials or approval with an engineer's or architect's stamp. With block construction, the material probably would not meet lateral load requirements and would need reinforcing unless it is used as an infill within large frame construction.
Papercrete has actually been around since the early 20th century but its recent rediscovery has shown it to be a cost-effective and flexible material. Any material that has the potential to divert waste from landfills and produce an intriguing and sustainable building product deserves ongoing attention.
Michael Cockram is an adjunct assistant professor of architecture at the University of Oregon. He is the director of the Italy Field School Program.
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