Use of flexible pond liners such as EPDM or PVC allows for a tremendous degree of customization in the design of the pond, but can be a bit tricky to install. With patience and diligence, and by adhering to the following guidelines, the desired results can be achieved with a minimum of grief.

Always start with a larger sheet of liner than seems to be called for. A surprising percentage of the excess will be absorbed into the various folds. It is wise to wait until the pond is excavated before purchasing the liner. Measure the sides and bottom of the hole in the two longest dimensions. To calculate the liner needed in either dimension, add the distance down each side of the hole plus the width of the floor, then add at least 1 m (3') extra.

Two or more pieces of liner can be seamed (joined) together if necessary, but it is always preferable to create the entire water feature out of one continuous sheet.

Seaming EPDM requires a cleaning agent (such as Firestone's Seam Prep), two-sided seam tape, finishing batten tape, and a lap sealant.

The most important ingredient in a successful seam is clean, dry joining surfaces. The cleaner should be applied with a course scrubber to take the shiny surface off of the liner. Cleaned surfaces can be dried with a hair dryer or heat gun if necessary - any wetness in the joining area will spoil the seam.

Seaming should always be done on a flat, solid surface to avoid bubbles, ripples and other mishaps.

A strip of seam tape is applied to one surface and is rolled with a laminate roller or similar device using moderate pressure in short diagonal strokes to achieve a pressure-actuated bond. The backing paper is then removed from the seam tape and the other piece of liner is placed over top and again rolled with moderate pressure. The batten tape is wider and has a cured outer surface. It is centered on the edge of the seam with backing paper removed and this too is rolled, paying extra attention to the edges. The edges of the batten tape are then caulked with a urethane lap sealant or marine sealant for added protection. The seam should be allowed to cure for at least one full day before the liner is moved.

Seaming PVC liner is much simpler as a liquid PVC bonding agent can be used.

Bonding agent is applied to both cleaned surfaces and allowed to tack off. Surfaces are then pressed together and rolled lightly with a laminate roller. The edge of the seam is caulked with lap sealant or marine sealant.

When arranging the liner in the pond, bunching will occur in corners and curved sections. Establishing straight, tapered folds will keep things tidy. There should be as few folds as possible (i.e. having a few large folds is better than having numerous smaller ones). Folds can be 'glued' flat if desired with marine sealant.

Trimming of excess liner should be left until the pond is fundamentally complete (the liner should never be 'pre-cut' before installation to the shape of the pond). Liners can be cut with heavy duty scissors or a strong utility knife. Be extremely careful with any cutting tool around the liner - never leave a knife open where it might fall and create a puncture.