Prepare the area to be repaired by cleaning it thoroughly with a wire brush.. Mix only a small amount of cement at a time, about a handful, as it sets in as little as 30 seconds. While kneading the cement ball with one hand, apply small amounts to the crack with the other, starting from the bottom. Smooth the edges before it sets. Work your way up the crack with more cement, repairing even above the water line. Speed of setting can be slowed by adding a small amount of conventional mortar mix to the hydraulic cement. Be cautious though since you want it to set in the water and not simply dissipate.

The repair is immediate and nothing else is required. Water can be added and, if the pond continues to lose water, look for another crack. For more information http://www.pondpro2000.com/epdm-pond-liner.html