RUBBER POND LINERS

Pond liners made from EPDM or Butyl synthetic rubbers are significantly more flexible and durable than liners made from plastics such as PVC or polyethylene. Deciding which of these two types of rubber is best for each project, and understanding the important differences between pond-grade rubbers and roofing rubbers, requires a rudimentary understanding of how synthetic rubbers are made and how they differ.

SYNTHETIC RUBBER: A synthetic rubber is made by mixing one or more rubber polymers-- the chemical backbones of rubbers responsible for their distinctive elastic properties-- together with oils, carbon-black, sulfur, and other substances that provide the desired color, flexibility, strength, and hardness. This mixture passes between massive steel rollers which squeeze it into a thin sheet of uncured rubber. Since uncured rubber is very sticky, it must either be dusted with mineral talc (talc-process) or layered between sheets of fabric (talc-free process) so that it can be rolled up without sticking to itself and fusing into one solid mass. The roll is then baked in an oven until it chemically cures into the elastic substance we normally think of as rubber.

EPDM RUBBER: EPDM is the name given to the class of synthetic rubbers made primarily from EPDM polymer, shorthand for Ethylene Propylene Diene Monomer. Although there are hundreds of ways to formulate EPDM rubber from EPDM polymer, all share a chemical structure that gives them extraordinary resistance to heat and air pollution. EPDM has been primarily used for waterproofing in exposed environments where long-term weatherability is essential, such as for waterproofing large flat roofs on commercial buildings. Since EPDM rubber can be formulated by combining a significant percentage of inexpensive oils and fillers with a fairly small percentage of EPDM polymer, it is relatively inexpensive to manufacture. As a consequence, EPDM rubbers made with the talc-process are among the lowest priced of all synthetic rubbers.

BUTYL RUBBER: Butyl rubber is the name given to the class of synthetic rubbers made primarily from butyl polymer. Although there are hundreds of ways to formulate Butyl rubber from butyl polymer, all share a chemical structure that gives them extraordinary resistance to moisture transmission and biological decay, as well as exceptional elasticity. Butyl has been primarily used for waterproofing in protected environments under earth or water where long-term durability is essential, such as for lining ponds, lakes, canals, reservoirs, and landfills. Butyl has also been widely used for waterproofing roofs of commercial buildings that are to be permanently covered with earth or concrete. Since Butyl rubber must be formulated substantially of expensive butyl polymer with very little filler material, it's relatively expensive to produce in comparison to EPDM.

VARIATIONS: The performance of synthetic rubbers for pond lining can be optimized by combining more than one rubber polymer in the formulation: for example, EPDM rubber can be made more elastic and more resistant to biological decay by adding Butyl polymer, and Butyl rubber can be made more resistant to heat and air pollution with the addition of EPDM polymer. The addition or omission of other ingredients can also affect performance of synthetic rubbers for pond lining: for example, certain curing compounds and fillers commonly used in Butyl and EPDM rubber can be toxic to aquatic life and must not be used in fish-safe formulations. Since any rubber made primarily of EPDM polymer can simply be called EPDM rubber, and any rubber made primarily from Butyl polymer can simply be called Butyl rubber, these names can be very misleading in the absence of additional information. In particular, be wary of inexpensive EPDM sheets since they may be fish-toxic roofing formulations.

THICKNESS: Thickness of synthetic rubbers is expressed in mils: one mil equals one-thousandth of an inch or one-fortieth of a millimeter. In general, the thickness of rubber has little effect on environmental aging characteristics of a liner, but can have a significant effect on the ease of installation and resistance to mechanical abuse. Irregular free-form garden ponds, especially those smaller than 2500 square feet, should be lined with 30 mil (0.75mm) rubber for the neatest results with the fewest folds. Larger free-form ponds, or small ponds with simple rectangular or elliptical shapes, can be successfully lined with 40 mil (1.0mm) or 45 mil (1.1mm) rubber. Recreational ponds, stormwater ponds, irrigation reservoirs, canals, artificial wetlands, and other large projects are usually lined with 60 mil (1.5mm) rubber since it is easier to seam and is considerably stronger than thinner sheets.

SEAMING: It is always best to line a pond with a single sheet of rubber. Since sizes up to 50 ft x 200 ft are standard, field seaming in residential-scale work can usually be limited to joining a stream or waterfall to a pond. Recreational ponds, reservoirs, and other projects too large to be lined with a single sheet of rubber can be reliably field-seamed with tacky rubber tapes and rubber/tape laminates that are cold-applied without specialized equipment. However, for field-seams to be effective the rubber must be cleaned with recommended solvents or with special cleaner/primers, the tapes must be applied carefully and with adequate pressure, and the liner must be positioned so as to prevent long-term seam stress. The procedure is not difficult, but it must be followed exactly and under the supervision of a conscientious contractor. (Please note that we do not recommend the use of contact adhesives commonly used for rubber roofing, since these adhesives are too weak and have insufficient resistance to ponded water to be reliable for seaming pond liners.)