A compactable mold comprises a main mold frame structure and plural wall structures including two end wall structures and two side wall structures. The plural wall structures define a mold cavity for forming a block from a mixture introduced into the mold cavity. At least two of the plural wall structures are movable wall structures for compacting the mixture. A described compactable mold has end walls and side walls that are shaped for forming tongue and groove features on a compacted block, and the end walls and side walls are movable such that a formed block can be released easily from the mold. A described compactable mold comprises at least one tube attached to at least one of the compacting wall structures. The compacting wall structures are operable to compact the mixture by moving toward the center of the mold cavity while the at least one tube remains stationary.