Formation finding: exploring soft cast MICP fabrication in a Water Kiln

Abstract Microbially Induced Calcium Carbonate Precipitation (MICP) provides a biologically driven alternative to conventional cementitious processes, requiring fabrication methods responsive to the dynamics of living systems. This study introduces a submerged soft-casting approach, employing fabric mesh moulds to biocement sand aggregates through the biomineralisation activity of Sporosarcina pasteurii . Developed in ‘Water Kiln’ bioreactors, the process replaces high-temperature curing with controlled liquid-phase mineralisation, generating cemented components assembled into the prototype column EmbryOme 1 . Rather than targeting structural material outputs, the research emphasises exploratory, process-oriented ‘formation finding’, where microbial activity, substrates, media and moulds together shape macro form and microstructure. Fabric casts filled with sand and nutrient-rich bacterial suspensions were submerged in cementation solutions to induce calcium carbonate precipitation. Key variables, including mould design, calcium and nutrient concentrations and media replacement frequency, were systematically adjusted to assess their effect on formation quality. Optimal outcomes occurred at 0.3 M calcium chloride and urea with daily medium replacement, and smaller mesh sizes produced denser, more uniform crusts. Cementation remained primarily superficial, though glazing treatments enhanced surface hardness. These results underscore the role of design in tuning biological–material interactions, framing biofabrication as a process of negotiation with material agency, variability and future architectural potential.