Pond Liners

by Dr. Adrian Lawler
(Retired) Aquarium Supervisor (l984-l998) J.L. Scott Aquarium Biloxi, MS 39530
Original to Aquarticles

At one time I had 31 ponds of various sizes and types on my personal property, which were used in raising various organisms for toxicity testing for 10 years, then used as growing/holding ponds for organisms used in the Scott Aquarium that I ran for 15 years. I used several types of liners over the last 32 years. My place was a test site on the use of HDPE liners for aquaculture by Gundle Lining Company in the l980's.

For using each type of the liners listed below, first dig a hole in the general shape and depth of the pond desired. Then, to ensure a compact, stable shape of the pond substrate under the liner, do the final sculpturing of the pond sides using hand trowels to keep the earth firm. Design the deepest part of the pond as a sump hole that can hold the pump you will use for pumping out your pond. Remove all protruding roots and pebbles to prevent liner puncture. Then line the hole with salt or a suitable herbicide, and/or old rugs or plastic, to deter root intrusion and possible liner puncture. Add sand to portions of the hole, if desired, to help prevent liner puncture and to give a smoother foundation for the weight of water to be above. Add a curbing 3-4" high around the top edge of the pond (under liner) to retard horizontal water flow into the pond during rains; level the curbing around the pond. Put a low section in the curbing for a spillway to handle pond overflow; at this low part vertically install plastic mesh screening inclined inward (after liner is installed) to retard fish escape during heavy rains. Install liner; and add water to help pull out liner wrinkles and to drive air from under the liner. You want to get as many wrinkles out as possible, because a wrinkle presents a projection that fish (and turtles) can bite to scrape algae from the liner, possibly leading to a leak. Dig a vertical trench 6-12" deep about 18" away from the edge of the pond to bury edges of liner to prevent horizontal water migration and erosion of soils under the liner.

All ponds should be filled and emptied several times to remove most of any toxins leaching from the clay, concrete, or liners. This process will take several days, or longer. When you think the water is safe, aerate the pond well, or let sit in sun a few days, to drive any chlorine out (if using city water). Then add a cheap healthy fish that will not cause a problem in the pond later and watch its reaction. Or you can put the fish in a floating cage so it can be easily removed from the pond after the testing is done. If the fish survives, add some submerged plants to help condition the water for a while. If the fish still looks healthy after a few days, and the pond water appears fairly clear, then you can assume the water is safe and you can add your main fish and plants to the pond. Various water tests can be done to verify water is safe.

All liner material NOT containing carbon black as a UV light retardant should have those portions out of the water covered with sand, dirt, sod, rocks, etc. to help prevent sun damage to the liner.

Those ponds with thin lining material should be protected against birds (kingfishers, egrets, herons, etc.) that will puncture the liner with their bills while pursuing your fish. They can puncture 40 mil liners. It is best to remove over-hanging branches so kingfishers will not have a branch over the pond to dive from, to make the pond deep enough so wading birds do not frequent the pond, and to design the pond so overhanging things (rocks, logs, plants, etc) are too high above the pond surface water level for perching birds to fish from. .

Clay
Allow for the thickness of clay when you sculpture your pond, so you get the final depth and size you want. Put a 2-4 inch layer of good clay around sides and bottom of pond and pack well. Test pond to see if water is held overnight. If the pond leaks, stir bentonite (drilling mud) into pond when full. A leaking pond will draw bentonite suspended in the water to the leaks and plug them. Bentonite can be gotten from local water well drillers. After water changes, and water has cleared of suspended bentonite, and after addition of plants, add fish.

Concrete
A concrete pond is initially labor intensive. Allow for the thickness of concrete when you dig your pond, so you get the final depth and size you want. Line the finished hole with visquine, put chicken wire on top of the plastic, and work concrete from the top down, getting a final thickness of 2-4 inches. When the concrete is fairly hard, use a large wet soft brush to give a smoother finish to the concrete. Over time the concrete might settle and crack; these cracks can be fixed with silicone cement or concrete patching material used for repairing concrete sewer pipe.

If you use forms to pour a concrete pond, or build cement block walls on a concrete base, then you should use a suitable sealant. One type I used at the Scott Aquarium was a non-toxic epoxy paint developed for concrete tanks; it gave excellent results in sealing plus gave the rough concrete surface a smooth finish.

HDPE (high density poly-ethylene, with carbon black)
This lining material is one of the best available, and is UV light resistant, lasting many years (generally 100 plus). It is used in lining under gasoline storage tanks, public dumps, toxic settling ponds, aquaculture ponds, etc. It can be heat-welded together; use 20-40 mil thickness for small ponds.

PE (poly-ethylene)
This is one of the cheapest ways to line a pond. The hole must be free of roots and debris. Pull 3-5 overlapping layers of the cheap visquine (usually 6 mil thick) into hole. If possible, use black visquine containing UV light retardant. If using clear visquine, hide portions out of water from sun (using dirt, sod, wood, rocks, etc). If leaks occur you can put two or more layers of new visquine over the initial layers.

Preformed ponds (HDPE, fiberglass, bathtub, wooden barrel, misc types of plastic, plastic barrel, etc) There are many types of preformed things that can be dug into the ground to use as a hole liner. After a suitable-sized hole is dug, the bottom of the hole is tamped down and leveled for a solid base, and the insert is added and allowed to stick up two or more inches above the surrounding ground level to prevent horizontal water flow into the pond. Soil is added around the edges and settled over several days by watering. Once the soil around the edges is settled, then one can fill the insert and leach out any toxins. Design a spillway into top edge of insert to handle pond overflow during rains; screen overflow to retard fish escape. This is probably the easiest way to make a lined pond.

One can also rest this type on the ground, and, depending on its wall strength, have it free-standing or supported around the sides with dirt, stones, bricks, etc.

PVC (poly vinyl chloride)
This type of material is used on flat roofs of buildings, with gravel to hold it down. In my area it can be recovered for free after hurricanes; I have seven ponds (three additional PVC ponds have been returned to land) lined with this material gotten after hurricane Elena took the roof off the Aquarium in 1985. The portion under water is still pliable and in good shape. Over the years that portion out of water, and exposed to sunlight, becomes very brittle and cracks/breaks up. That portion under water will last for many years. Protect portions exposed to sun with dirt, gravel, etc.

Vinyl
One of the cheaper liners, usually the type used in home swimming pools. Fairly easy to puncture or tear; must have a clean hole so liner is not torn by roots, and other hard debris. One fish farm I worked with lost thousands of dollars worth of tilapia when the tilapia punctured this type of liner by scraping the algae off the liner with their teeth, leading to a sudden blowout. When liner is installed it should have as few wrinkles as possible so fish cannot bite on liner. Suggest putting sand on top of liner to also protect it from punctures from within the pond (birds, fish spines, decorations, plant pots, etc). Protect portions exposed to sun with dirt, gravel, overhangs, etc.