Properly sealing the joints between adjacent EPS Cement Sandwich Panel units is one of the most critical steps of the entire installation process, and doing this work correctly will ensure your finished wall system stays completely weathertight and airtight for many years. First, make sure the edges of both adjacent EPS Cement Sandwich Panel units are completely dry, free of dust, loose cement particles, and any construction debris before you position them together. Leave a small consistent gap of 3 to 5 millimeters between each panel edge, rather than pushing them tightly together, to give the material a small amount of room for natural thermal expansion and contraction with seasonal temperature changes. For interior wall joints, you can use a standard flexible acrylic sealant to fill the gap, then cover the joint with a self adhesive fiberglass mesh tape, before applying a thin layer of joint compound to smooth the joint completely flush with the rest of the panel surface. For exterior wall joints that need to be fully waterproof, use a high quality polyurethane or neutral cure silicone sealant that is specifically rated for outdoor weather exposure. Once the sealant is fully cured, you will have a completely continuous, airtight and waterproof wall system that prevents air leaks and rain water from penetrating through any gaps between the EPS Cement Sandwich Panel units.