In the 1940s during a period of intense housing shortages across the French Protectorate in Morocco, a group of engineers founded the Laboratory of Building and Public Works (LBTP) in Casablanca. This institution—a site for testing local construction materials—was part of larger a network of colonial laboratories stretching from Algiers to Brazzaville. This paper will take up a series of arguments within North African history and colonial studies more broadly about what it means to describe a “colony” or a “colonial city” as a “laboratory” for modernity, social reform, or urbanism. This paper will reevaluate the vision of the “laboratory” at stake in North Africanist claims that colonies acted as laboratories through an engagement with ethnographies of laboratory practice within Science and Technology Studies (STS). In reassessing the figure of the “colony as laboratory” within colonial studies and Maghrebi history this paper will also consider how the understanding of what a laboratory is shifts when the laboratory in question is a colonial laboratory, such as the LBTP in Casablanca. The network of scientific institutions that included Casablanca’s lab defined their project not in terms of creating universal or transferable knowledge, but as an attempt to demarcate the very boundaries of the “local.” While testing the performance of various materials, Casablanca’s LBTP defined Morocco itself as an experimental space. Studies produced by the LBTP network also demonstrated the barriers to the circulation of new construction technologies—limits derived from a particular way of seeing colonial climates, environments, geologies, and labor forces. By examining a series of reports produced by these laboratories along with supporting archival materials, I will analyze how the LBTPs elaborated a program for defining locality in an imperial context that would continue to shape laboratory practices in Morocco after the end of the Protectorate. The conclusion of this chapter will consider expert efforts to extend ways of measuring matter and organizing labor from the laboratory to the Protectorate’s construction sites. For European engineers working in Morocco, managing the construction site was a question of mastering and mobilizing “the local”— whether the peculiar and unpredictable qualities of local materials or the misunderstood skills of Moroccan laborers and artisans.