A morphological change observed during fabric formed rammed earth construction process is an interesting performance that cannot be found in rigid formwork such as timber formwork or steel shuttering. In this blog post, I would like to show how the two materials - rammed earth and fabric perform in fabric formwork based on my recent rammed earth doghouse construction.
The morphological change revealed throughout fabric formwork construction process demonstrates how materials can play an active role in forming a shape. Before ramming soils, fabric on the formwork hung limply. But during the ramming course, the fabric stretches by a tensile force under compaction, but its deformation is constrained by vertical timber frames. The fabric of the flexible formwork looks flaccid at first glance, but it gradually gains a monolithic appearance being filled with earthen mixture. The flexibility of the fabric unfolds a dramatic change of the form throughout the construction process. If rammed earth is fabricated with rigid formwork, the interesting morphological transformation cannot be observed. As for rigid formwork, the relationship between material and designers is unilateral as material is required to produce the shape a designer pre-designd. On the other hand, flexible formwork extends the scope to which materials, designers and builders are actively engaged. Materials acts as “active design generators” * exhibiting its performance throughout a construction process and its performance is controlled to some extent by shuttering pre-designed by a designer (In this case, I used vertical timber frames to control the bulging of the fabric). The outcome of rammed earth is also influenced by the compaction conducted by a builder. According to the level of the compaction, the density of rammed earth varies from porous to dense surface.
One of interesting features of fabric formwork is that the fabric lends its property to rammed earth - the seams and wrinkles of the fabric are embedded into the rammed earth surface causing an optical illusion that the monolithic structure is lightweight and flexible like fabric. This is a clear trace of the active performance of the materials created by tensile force and compaction.
Once fabric formwork was dismantled, the fabric returned to its original state. Although it had been stretched to its maximum level by tensile force, the PE fabric is so resilient and sturdy that it finds its original woven state even after the intensive activity of compaction is conducted. This demonstrates how flexible fabric formwork is. The used fabric is reusable for a next fabric formwork or other purpose such as weed barrier.
After the fabric formwork is removed, the embedded curvatures were clearly discovered on the rammed earth creating rhythmic volume.
During the ramming course, I realised I should have reversed the seam. When I removed the fabric formwork, the seam of the fabric was caught by the rammed earth cast, I struggled to pull the fabric in order to remove. Although I managed to take it out, if the seam had been more deeply embedded, it would have been impossible to remove the fabric completely. The place where the seam had been left a clear ‘scar’ on the rammed earth, so I think it needs to be applied with a mud plaster to cover in order to prevent freeze-thaw damage in the upcoming winter.
In the next post, I am going to share the construction process of creating mud roof with fabric. To keep updated with the next post, follow my Facebook page or Instagram.
* The term is quoted from Achim Menges in Material Computation, Architectural Design 2012.