Joining sheets of EPDM is actually a relatively simple process if you approach it with patience and attention to detail. The most important consideration is achieving a strong, complete seal. Therefore, it's best to work on a clean, dry, flat surface to ensure you can achieve a perfect, watertight seam. A sheet of plywood or even a length of 2x10 board will work quite well. When seaming EPDM, plan for an overlap of 5". If there's grime or dust on your liner material, start with a mild household cleaner, rinse it thoroughly and allow it to dry completely.
Apply primer to the seam area on both pieces of the liner and allow it to dry according to the instructions on the bottle or can. Apply seam tape to the bottom layer as precisely as possible with backing paper facing upwards. You won't get any second chances here, so go slowly and be precise! Once it's in place, use a roller to get a strong bond between the liner and the seam tape. Next, lay the top liner over the seam tape (backing paper still in place) and press the top liner into position as you slowly pull off the tape. Finally, roll the entire seam from end to end, then across the seam to ensure complete adhesion.
