In this study, epoxy–cement composites with different concentrations of cement nanofiller and ~67.5 nm in size (0, 5, 10, 15, and 20 wt%) were synthesized using the solution casting method. The epoxy–cement composites’ structural, mechanical, wettability, roughness, and thermal insulation were investigated. The synthesized epoxy resin is amorphous, whereasepoxy–cementcompositesarecrystalline, and its crystallinity dependson the filler ratio. The incorporated cement hindered the spread of cracks and voids in the composite with few illuminated regions, and the epoxy/cement interface was identified. The Shore D hardness, impact strength, and flexural strength gradually increased to 92.3, 6.1 kJ/m2, and 40.6 MPa, respectively, with an increase in the cement ratio up to 20 wt%. In contrast, the incorporation of a cement ratio of up to 20 wt% reduced thermal conductivity from 0.22 to 0.16 W/m·K.Thesefindingsindicatedthat resin andcementnanoparticle fillers affected the chemical composition of epoxy, which resulted in high molecular compaction and thus strong mechanical resistance and enhanced thermal insulation. The roughness and water contact angle (WCA) of epoxy increased by increasing the cement nanofiller. In contrast, the surface energy (γ) of a solid surface decreased, indicating an inverse relation compared to the behavior of roughness and WCA. The reduction in γ and the creation of a rough surface with higher WCA can produce a suitable hydrophobic surface of lower wettability on the epoxy surface. Accordingly, the developed epoxy–cement composites benefit building construction requirements, among other engineering applications.