Joining EPDM rubber pond liner may seem like a difficult task, but with some planning and patience you can join two pond liners together with a leak-free seam quite easily. Here are the steps needed to make a proper seam with EPDM pond liner using 3″ wide double-sided seam tape.

1. Make sure the liners you are joining are clean and dry before starting.
2. Position the first piece EPDM rubber liner on a flat smooth surface. If you don’t have a flat surface to work on, lay a piece of plywood or 2×10 board under the seam area to make a smooth surface to work on.
3. Position the second piece of EPDM rubber liner on top of the first and overlap the edge by 5”. Mark the edge of the liner with chalk, then fold it back 12”.
4. Apply quick prime or quick prime spray adhesive to the seam area on both pieces of liner and allow to dry, usually about 10 minutes.
5. Apply the 3” double sided seam tape to the primed bottom liner with the backing paper side facing up. Be very careful to align the edge of the backing paper along the chalk line of the bottom liner, the seam tape is very sticky and you will only get one chance to position it correctly. Once in place, use a roller to firmly set the seam seam tape to the  liner (without removing the backing paper) .
6. Lay the top liner back over the seam tape with the backing paper still in place. The backing paper should extend ½” past the top liner. If the top liner extends past the paper backing, the liner should be trimmed or pulled back.
7. Starting at one end of the seam, slowly and steadily peel the backing paper away from the seam tape at a 45° angle and gently push the top liner onto the seam tape until all of the backing paper is removed.
8. Roll the entire seam with a roller along the length of the seam and then across the seam to ensure adhesion.
9. Once complete, the liner can be put in place and used immediately.