Pleased that the first phases of the modelling process had been a success, I then wanted to push it further and try and cast in the formwork as well.
I knew that it was likely that the card formwork would have to be sacrificial, so I made sure to get plenty of photographs of it both on its own and integrated into the bamboo forest first. Then, I removed it from the base and took it to the workshop, and then bought a substantial quantity of plaster!
I had two possible options for how to add the cast material. One would be to build up layers of it on the card by 'painting' on the plaster. This would leave me with 'columns' as hollow spaces, which is my intention for the scheme at full-size, at the moment, as these could become places to collect and store rainwater, or be filled in with soil to grow things. The other option was to pour plaster in and fill it right up to the top, making the whole thing solid. I decided to take this approach, because I felt it had a greater chance of being successful, and as the formwork had been quite complicated to assemble and would likely be lost in the process, I wanted to ensure that I got something of value out of it.
Having decided on the pouring process, I knew that the card formwork would be subject to a great deal of hydrostatic pressure, as there would be a large volume of plaster. Also, as I was going to be pouring the plaster in in a very liquid state, there would be a risk of it leaking out of the base. To tackle these issues, I sealed between the formwork and the work surface with masking tape, and also braced it between heavy concrete blocks to support it against the lateral hydrostatic forces.
Formwork base sealed with masking tape prior to casting
I then began pouring in plaster, layer upon layer. Over the arch sections, I also added some modroc reinforcement, to prevent it cracking in what would be the weaker points.
Casting process, showing the formwork braced between two heavy concrete blocks
After leaving it overnight to begin to dry, I then removed the card formwork, cutting and tearing it away. Overall, I was really happy with the result, as I had no idea if it would work beforehand. I was very pleased that it didn't crack, and also that it picked up the faceted geometry really nicely. If I wanted to, I could now sand down the surface where there are parts of the formwork stuck to the surface, but I quite like the effect it has, as a remnant and reminder of the casting process.
Process of removing the formwork
Close-up of the cast, showing the faceted detailing and remnants of the formwork on the surface
Sacrificial formwork once removed
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