Documenting a personal quest for non-toxic housing.
Saturday, February 28, 2004New Technology
I've recently learned of an interesting new variation on the Monolithic Dome technique being offered by a company called Domeshells Technology in Australia. The Monolithic Dome technique is based on the use of a pneumatic form which is inflated atop a simple slab foundation. Polyfoam is sprayed on the interior of the form and then a reinforcement mesh is applied to which a coating of shotcrete is applied to make a rigid structure. The pneumatic form remains in place as a proective covering for the insulation. This is a popular building method for dome homes but it has its limitations. The technique has never realized a significant savings over conventional construction, in part because the most expensive part of a 'kit' -the pneumatic form- cannot be reused. And the exterior plastic skin of this form is short-lived and must be repeatedly treated with paints in order to maintain its integrity.
In this new Domeshell technique a pneumatic form is inflated on a slab as with the Monolithic method but polyfoam is sprayed on the exterior in a layer thick enough to form a free-standing shell. The form is then removed for reuse. The foam shell is then simply covered in layers of fiberglass reinforced concrete on both sides and finished in plaster, stucco, or paint. No reinforcement mesh is needed because of the fiberglass reinforcement mixed into the concrete. This seems a much easier construction process. The Domeshell designs also offer some further advantages. With a high near-vertical riser, the domes are easier to fit conventional furnishings into. They also have portals for windows and doors pre-formed and the shells are easily clustered together at these points to make homes of any size. Clustering is a much more practical approach to the use of domed structures than the more common partitioning because one can dedicate individual rooms to single relatively small and easy to make units. This has been difficult to do with the Monolithic domes because they need special add-ons and form customization to accommodate clustering.
An interesting aspect of this new dome method is the way the fiberglass reinforced concrete eliminates the use of metal mesh reinforcement and is applied directly to the polyfoam. Building in foam insulation has always been tricky with ferro-cement structures because of the need to use mesh to support and define the shape of any individual concrete shell structure. Two such shells are needed to allow injection of polyfoam or other forms of insulation material. But here we see an approach that basically starts with the insulation defining the structural shape and then being made durable by the application of concrete without mesh to support it.
This offers a lot of potential design freedom. One is essentially free to design the exterior and interior shapes of structures independent of one another, except where they meet at portals for doors and windows, as long as whatever interior shapes collectively fit within the volume of the exterior shape. One would create rough shapes in polyfoam, pumice-crete, or foamed concrete and hand shape them with cutting/grinding tools into the finished form before applying the final concrete shell layers. High load bearing structures will still require metal reinforcement but this approach should be suitable for many structures within one or two storeys and would be well suited to designs employing mimicry of natural geological or botanical shapes.
