Collaborative Mixed Reality (MR) systems that help extend expertise for physical tasks to remote environments often situate experts in an immersive view of the task environment to bring the collaboration closer to collocated settings. In this paper, we design UnMapped, an alternative interface for remote experts that combines a live 3D view of the active space within the novice’s environment with a static 3D recreation of the expert’s own workspace to leverage their existing spatial memories within it. We evaluate the impact of this approach on single and repeated use of collaborative MR systems for remote guidance through a comparative study. Our results indicate that despite having a limited understanding of the novice’s environment, using an UnMapped interface increased performance and communication efficiency while reducing experts’ task load. We also outline the various affordances of providing remote experts with a familiar and spatially-stable environment to assist novices.