Cotton Formed Columns

November 14, 2010

 

First prototype column cast in its formwork

Prototype Column – Discovery through doing

These last few weeks have been an incredible learning curve from the previous post – post-rationalising is important however in a process where technique evolves through production, analysis and improvement.

Our fabric formed concrete has evolved in such a way, quickly moving from the horizontally cast wall panels to familiarising ourselves with the technique of casting vertical column elements. There are only three of us in the unit and we quickly learnt that producing larger pieces requires good team work, ideas from each of us and man-hours to construct the formwork, cast effectively – and to succeed.

We analysed previous projects completed in 5 week workshops that have run over the last four years. Our intention was to take the wealth of experience and knowledge of past experiments and develop these techniques, refine them or even find a new direction to pursue. We were intrigued by a column that clamped the fabric to create voids by preventing the concrete filling certain areas. We liked the thought sewing a void in the fabric instead of using clamps. This technique had scope for further investigation.

The First prototype Column

The first prototype column is an irregular ‘Y’ shape with two voids. The central void was created using shaped MDF clamps, the other void was created by stitching the cotton along the top to create a final structure that read as a ‘y’. We quickly realised that stitching is an important technique in the production of the formwork and the decision to explore the possibilities and limitations of sewing the fabric was taken from there.

Prototype column initial sketch

The best way to design the column was to chalk the outline of the column directly on to the black cotton fabric. From the two-dimensional layout we calculated the diameter of the holes left open at the top – in order to construct the top plate from which the fabric would be hung and pulled into tension. Using a sewing machine we stitched along the lines to fix the shape into the fabric and prevent the concrete flowing into those areas.

Attaching fabric to the formwork

Rigging the base was tricky. A fabric wants to go into a cylinder, but we had prepared a square base so it crumpled up over the ledge. However, the final results are quite pleasing – there is an essence of a classical statue to the form. Constructing the top plate was straight forward using a jigsaw to cut an ellipse and a circle connected by a slit to feed the sewn fabric through. We ensured that the fabric was in tension and top of the column was level, stapling it to the top plate.

Top plate fixing before the pour

Casting and Patching

Patching during the pour

Our mix was probably not quite fluid enough and our first attempt at an arm was quite narrow resulting in aggregate getting stuck at the top and causing a frantic effort to force the aggregate into the arm and compact it sufficiently. In the process of solving this, we didn’t manage to push a steel reinforcing bar into the arm and we were wary that we hadn’t managed to compact the base of the arm well enough. A more serious problem arose, however, when we noticed that we had accidentally pierced the fabric in a couple of places with the vibrating rod. This required some emergency patchwork using excess fabric, pulling it around the arm and stapling it to the central clamp. We prevented the leak, but the evidence is still visible in the final cast – like the scars of construction visible like a bullet hole. Honesty and evidence of construction is important so Louis Kahn would be pleased.

A Greek form?

First Prototype column

Once the column had been ‘peeled’ after a few days curing, we enjoyed the results of our first column cast. The surface finish of the cotton was visible on the surface and the form was very appealing. Another noticeable and informative difference was the quality of finish between the clamped void and the seam stitched void.

The stitched seam was prominent on the surface of the concrete, where it had been rubbed into the surface of the wet cement. The are that was clamped had a rougher surface finish and a different colour, because it wasn’t possible to rub that area in contact with the cement.

The convenience, possibilities and effect created using stitching was an important discovery that we developed in all the following work.

Detail image of the stitched void, visible on the surface of the concrete

Verticle view showing the delicacy of the structure

The first column in the foreground with the next two in the background

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