A plastic formwork is disclosed, and comprises a slurry-receiving structure, wherein the slurry-receiving structure defines an aperture and a formwork-defined internal space, wherein a slurry is receivable within the formwork-defined internal space. The formwork further comprises a formwork-defined first connection system counterpart and a formwork-defined second connection system counterpart, each of which includes a sealed interface-effecting portion that is supported by a substrate portion. The material of the sealed interface-effecting portion is softer than the material of the substrate portion. The formwork is connectible to another formwork via interlocking engagement with effect that an obtained aperture and an obtained internal space are obtained, wherein a slurry is receivable within the obtained internal space. The interlocking engagement is with effect that sealing engagement is effected between the sealed interface-effecting portions of the formwork and the another formwork such that sealed interfaces are obtained between the formwork and the another formwork.