This is clay which has had the air pushed out of it, via the hands or feet during construction of a pond. (ref) If locally sourced, the clay can be very cheap, however the cost gets greater, for the environment and yourself, if it is transported to you from further away. (ref) Whilst hard to install at first, the clay lining won’t crack, as long as the topsoil doesn’t move and the pond is filled to capacity. (ref) Clay is natural which provides a habitat for bacteria, microorganisms etc. to flourish, having benefits for fish and other wildlife. (ref) The clay is thicker than most other liners, which means a larger pond will need to be constructed, however. (ref)
A common material for pond lining, many different types of rubber can be used, with butyl and EPDM being examples of widely used rubbers. Both liners will last around 20-50 years and are non-toxic to nature. (ref), They are both flexible too, being easy to fit, however, EPDM is usually thicker and harder to work with. (ref) Their creation will cause pollution, but the long lifespan can spread the damage over a period of time. (ref) Regardless, the rubber will be either synthetic or natural, and neither is made in a sustainable fashion wide-scale. (ref) The material can also rip but is easily repaired. (ref) The liners will also need an underlay, usually sand, which can contribute to the sand crisis. However, old synthetic carpets can be an alternative to sand. (ref) At the end of its lifespan, the rubber will decompose for around 80 years. (ref)
Flexible plastics can also be used for the construction of a pond, PVC and reinforced polyethylene being examples. Stronger, more rigid pre-formed linings can also be made from plastics, which tend to be easy to maintain and some can even encourage healthy bacteria growth. (ref) Much like rubber, plastic liners will need to be made, creating pollution in this process, but the time of usage spreads the damage out over time, (ref) synthetic carpets can also be used as an underlay as opposed to sand. (ref) Plastic liners can last decades, (ref) but can be damaged fairly easily (in relation to concrete etc.) (ref) and will eventually need to be replaced. Plastics can take hundreds to thousands of years to decompose (ref) and are mostly made from crude oil, (ref) which perpetuates the need for oil and its un-sustainability.
This material is the most durable when it comes to ponds (ref) and can withstand trampling. (ref) In its creation, it will interfere with the existing environment, making it harder to establish a new habitat. (ref) Concrete can be expensive and time-consuming in its creation too. (ref) If the material does crack, it can be extremely hard to fix. (ref) Along with this, concrete uses sand in its creation, which is a rapidly depleting resource. Concrete itself is also very polluting and contributes massively to CO2 emissions and climate change.
Fibreglass (pre-formed lining)
A very durable material, (ref) its pre-made structure eliminates the possibility of folding and creases (ref) and is hard to penetrate. (ref) Fibreglass can be a finishing touch to preformed bases, made from concrete or plastic. (ref) However, the material can be costly, and not be as attractive to wildlife as other materials. (ref) Along with this, fibreglass cannot be recycled widely, (ref) meaning that it can stay in landfills for a long period of time. It is made from silica (sand), which can perpetuate the sand crisis, but also decomposes at a slow rate, potentially lasting 1 million years. (ref)
Pond Lining Summary
Each material for a pond has different benefits and costs, however, from a sustainability perspective, puddled clay is the most environmentally friendly. However, rubber may be an alternative to clay if it is not viable.