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Ecodur 201: DIY Pond Lining Project

There are hundreds of thousands of ponds worldwide all the way from little backyard ones with some hardy goldfish to very large ones for fish and shrimp cultivation. But what they all have in common is the need retain water purity sufficient for keeping the pond life healthy. To that end many are lined with EPDM, butyl rubber, or concrete to prevent water seeping away into the ground. There are also bathing pools that replicate natural ponds having an area specifically relegated to reed and other pond plants that help act as a natural filter. Artificial ponds like this are popular in Europe but in their infancy in North America.


A man-made pond is essentially an artificial habitat and the problem is to ensure that it becomes as close to being a natural environment as is possible so it can also sustain additional animal and plant life creating a balanced eco system that responds in a harmonious way with the seasons.

With this being an attempt to create an Eco Pond all the elements had to fulfil the mandate as far as possible. The key initial focus is getting the right pond lining that is inert, non-toxic and robust. Commonly used Ethylene Propylene Diene Monomer (EPDM) and butyl linings are generally effective.

In this case study, Castagra’s Ecodur was chosen because it as close to being a natural product as is possible with it being specifically rated for contact with potable water was used. It is free of volatile organic compounds, BPA-free, and, most importantly, completely biologically inert.


It is made from castor oil and a commonly found mineral, gypsum, which is a calcium sulphate dihydrate that occurs naturally. When the vegetable oil and gypsum are combined, the final product is essentially plasticised gypsum – literally a soft rock. Its retained flexibility and abrasion resistance, makes it highly suitable for a pond lining that can have large stones and plants placed upon a bed that might also contain objects that would threaten the integrity of less robust material.

Application Results
The two-part pond, in the garden of a home in Seattle, Washington, was basically constructed with straight sides and concrete walls for maximum strength. In order to make the exposed surface as natural as possible, Ecodur was applied to provide the neutral barrier. Its outstanding retained flexibility also ensures that even in the harshest of winter climates it will maintain its integrity, even under the pressure of ice.


The top chamber from which the water cascades into the main pond has been designed as a natural water filtering bog. Bog plants will be added to naturally filter the water. They will get their nutrition in part from the waste of fish that live in the main pool. There is a large central pipe that connects the main pool to a “settling chamber” which also contains the pump so the waste from the main pond is sucked into it and settles in there. It will only need to be mucked out once a year, largely as a result of the build-up of harmless organic matter. The owner has reported that his Eco Pond has met expectations with the ‘bog’ steadily achieving the natural state that is key to completing the circle of bioactivity necessary for the purity of the water and the elimination of fish waste.