Pond edging serves many purposes. The first purpose of pond edging is to create a defined and stable border to prevent erosion of the ground around the water. Another purpose is to make a berm that prevents water runoff from the containment area. Finally, a pond edging allows you to develop the scenery to match your own personality and taste. Edging can be sharp and sparse rock and boulders, or soft, natural grasses and plants. It also may include focal points of rock structures, or floral arrangements. All of the possibilities for a pond's appearance begin with a solid edging.
Lay out flagstones around the edge of the pond area, overlapping the edge by at least 5 cm (2 inches). Whether you design the layout in an orderly, side-by-side stone setting, or lay irregularly shaped stones for a rugged, natural look, always lay out the flagstones first before setting them in cement so you have an exact pattern to follow. You'll also know ahead of time that you have plenty of stones to complete your pond edge.
Lay any required pipes, hoses or tubing in trenches before cementing the stones in place.
Mix cement in a three-to-one mix of sand and cement to make a strong, thick mortar. Mix in waterproofing additive with the mortar to make the cement impenetrable by water and to make the pond edging last longer.
Remove the flagstones from a small section of the pattern and lay a smooth layer of mortar with a trowel. Turn the trowel to the ribbed side and drag it over the mortar to create even ridges in the cement that will give the mortar more suction.
Tamp each stone in place with a rubber hammer. Make sure each stone is level with the others by laying a carpenter's level across them as you go. Avoid tamping too hard by using as little mortar as possible, while still giving the stones enough cement to set into. Too much mortar makes it necessary for you to tamp the stones down hard. This can squeeze excess cement over the edges into the pond.
Add native grasses and decorative plants around the edges of the pond and at the back edge of the stones, as well as in planned spaces in the flagstones, if desired. Adding perennial plants and grass will give the area a softer, more natural edge. Make the edge of your pond less formal by substituting 60 cm to 90 cm (2 to 3 foot) boulders for some (or all) of the flagstones for a more rugged look.