Approving the use of a floating cover made from geomembrane for your project isn’t the only step in design or selection. The material used to construct the floating cover will largely determine if it lasts for years and whether or not it achieves your goals. Improper material selection leads to a liner that cracks in the cold, peels apart in the sun, or simply sinks below the surface of the water despite the use of floats. Find out what materials are commonly used for both rigid and flexible floating covers, how to choose a geomembrane, and what to consider when planning for seams between pieces of material.
Specific Material Options for Geomembranes
There are dozens of different geomembrane products on the market today sold specifically for floating cover use. However, not all of them offer the same combination of durability, flexibility, or UV and chemical resistance. Here are the most common options you’ll find and how they compare to each other.
Chlorosulfinated Polyethylene (CSPE)
As a type of polyethylene, CSPE manages to offer both UV resistance and high levels of flexibility in the same product. Unfortunately, this material is best suited to fresh water covers and use with only a limited number of wastewater mixtures. It simply can’t handle conditions that are high in fats, oils, or hydrocarbons without reacting and breaking down. Chemical and corrosion resistance otherwise is good, but not great. This was once the primary material used for floating covers in the early stages of the method’s development, but better materials are available today.
Polyurethane (PU)
Almost all floating covers include polyurethane in some way because it’s the material used for creating high buoyancy and chemical resistance foam blocks for the floats and supports. However, some manufacturers also use it to create flat and flexible geomembranes. This material isn’t tear and crack resistant enough in that format to make a good liner or cover for a pond. Stick to PU for the foam and choose another material for the cover itself.
Polyvinyl Chloride (PVC)
PVC is a widely available material commonly recommended for recreational and decorative ponds. It’s not as good at holding up in challenging industrial or storage situations that would require a long-term cover. If gas will be putting pressure on the liner from the inside, PVC is particularly prone to tearing or rupturing unless it is reinforced. Even reinforced PVC lacks the chemical and UV resistance of other materials like RPE and even CSPE. Avoid PVC for covers unless they’re temporary and it’s the only material available in the area.
Polypropylene (PPE)
PPE often sounds like the ideal floating cover material because it is highly UV and chemical resistant, less likely to crack when cold than many other materials, and it’s very flexible. However, it lacks durability and strength in other ways and is prone to tearing when installed as a cover that’s constantly exposed to changing stresses. It’s also rarely reinforced, making it less resistant to wind and friction damage over time. Finally, it must be installed in thicker sheets than other materials to offer the same amount of insulation or longevity. Avoid PPE for most floating liner covers unless there’s a particular chemical exposure challenge you need to overcome.
Reinforced Polyethylene (RPE)
For the best combination of UV resistance, cold and hot performance, tear and chemical resistance, as well as affordability, look for a reinforced polyethylene liner. RPE is a combination of different polyethylene polymers bonded around a core of reinforcement scrim to make a material that is both highly flexible and durable at the same time. RPE also offers extensive custom fabrication options so there’s little to no need to install seams on-site when assembling the cover system. For a liner you can walk across and maintain without concerns of damage, turn to BTL Liners for RPE cover products.
Seams and Covers
Do whatever you can during the design and material selection phases of the project to minimize the number of seams in the cover. While seams are expensive and prone to leaking when used to seal a pond liner together, they’re even more troublesome in covers. Since the cover will primarily lose invisible and hard to detect gases through seam leaks, they often go years without detection. Using a single sheet of material with minimal or no seams, is the best way to prevent invisible gas leaks. Look for a manufacturer, like BTL Liners, capable of custom fabrication to order a cover that will fit the entire pond or tank in a continuous sheet.
Matching the Liner
It is helpful to choose a cover made of the same material as the liner because this allows for chemical or heat welding treatments at the edges to create a continuous barrier for containing gases. However, this is not a requirement in systems relying on attachment points around the edge of a tank or raised side pond. In most cases, you should choose a cover material based more on its features and functions rather than if it matches the liner material or not. If you’re constructing the entire pond from scratch rather than covering it after the fact, it’s much easier to choose matching or compatible materials for both the upper and lower parts of the containment system.
Is Insulation Important?
Insulated floating covers are most commonly used in sewage treatment plants located in cold climates where temperatures regularly drop below the 60 degrees F that is optimal for processing. However, they’re also used for any drinking water supply or chemical storage tank that needs to stay above freezing in the winter. The cover itself generally supplies insulation through the foam alone, but some materials like RPE can also boost the total insulation value slightly.
If you’re covering a fresh water supply that will be distributed to businesses and homes without further treatment, make sure both the liner and cover materials are rated by the NSF for potable water use. Other liners and covers can leach chemicals into the water that are unsafe for long-term consumption, especially when you add chlorine and other water treatments into the mix. BTL Liners is happy to help you find an NSF rated liner or cover to complete your potable water storage project.
