As the housing deficit problem is a general present reality for low-income families, it is opportune to find alternative ways of building popular houses, with the aim of improving their conditions of use, such as thermal comfort, which is directly related to the well-being of users. In this perspective, the present work intends to investigate the thermal performance of cement slab with the use of expanded vermiculite in its composition, in certain percentages of 0%, 25%, 50% and 75% of substitution by the clay used in the reference mix proportion. In addition, it is also the task of the study to verify the mechanical properties of tensile strength in flexion and compressive strength of the mortars in each mix proportions. The research offers results from experimental studies preceded by a consistent theoretical foundation. To analyze the thermal performance, sealing panels composed of the produced cementitious plates and a wooden structure were made. This test consisted of a prototype that simulates the irradiation of the sun on the panels, evaluating the possible thermal insulation of the internal environment in relation to the external environment in the buildings. In the case of mechanical properties tests, they were based on NBR 13279:2005. The results point to the improvement in the environmental comfort afforded by the use of the slabs with mix proportion of 50% of clay substitution by the light aggregate under study and indicate a decrease in tensile strength in flexion and compression as the percentage of vermiculite increases.