Subtractable materials

Subtractive fabrication presupposes a main block of material which will be carved or cut in order to reveal the “statue inside it”. This material is usually provided in the form of rectangular cuboids. Following, a tentative list of subtractable materials:

• Stone – A natural, hard material, of which various types exist with different compression and tension resistances, and geographical availability. Although available in many stock sizes, Brandon Clifford, McGee, and Muhonen (2018) speculate on the possibility to use irregular rubble to fabricate voussoirs.
• Wood – Historically associated with roof framing structures, or temporary centerings, its properties make it suitable for voussoir modelling, such as in Voute de LeFêvre (Brandon Clifford and McGee, 2014). The natural dimension of tree trunks and branches limit the maximum thickness of wood blocks, which is overcome by gluing large boards together.
• Foam – Very light and easy to machine, this material’s most interesting property is its similarity with stone, making it suitable for prototyping (Azambuja Varela and Sousa, 2015). Its maindisadvantageistheassociatedcarbonfootprintmorethantwentytimescomparedtoother materials such as precast concrete (Ruuska, 2013).
• Cork – In the form of Expanded Insulation Corkboard (ICB ), this material has a high sustainability performance (Sousa and Duarte, 2012) and, besides being light and easy to machine, it can also withstand diverse weather conditions. Its main drawbacks are its relative compressibility, which may introduce deformations in the general macro-shape.