Pond liner ... Difference Between Butyl Rubber and EPDM For Pond Lining

QUESTION: I am in the process of digging out a pond 4 x 3.5 x 1.2m deep (14 x 12 x 4ft). However, I have hit a stumbling block regarding what liner to use. I intend to use a butyl liner of 0.75mm thickness but have read in my magazine to beware of different blends of butyl.

However, when I have asked various aquatic centres about the amount of butyl in the liners they sell (the EDPM), some of them do not know what I am talking about and just say they are 100% butyl with a lifetime guarantee. The only one I can find with an EDPM ratio is of 80:20, whereas I was under the impression a 70:30 ratio is a higher grade. Could you please advise me if possible where I can buy a butyl liner with this 70:30 ratio of butyl in it?

ANSWER:

The answer to your problem is highly technical, but put simply, although EPDM and BUTYL RUBBER seem very similar materials, at a molecular level and in the manufacturing process they are quite different materials. Most of the supply of both these materials in this country are manufactured by no more than two extremely reliable and prestigious companies each. For EPDM I have always used a Firestone brand since that is what my local supplier stocks. For BUTYL I have always used Värnamo from Sweden, but I think both comapies make both products. For a brief description of what they consist of I will quote from Värnamo’s PR literature.

The description of the separate materials is as follows!

”Butyl: The polymer butyl (IIR - isobutylene isoprene - rubber) is an elastomer with a small number of double bonds, produced through co-polymerisation of isobutylene and isoprene.

EPDM: The polymer EPDM, ethylene-propylene rubber, is produced through co-polymerisation of ethylene, propylene and diene monomer, producing a polymer made up of saturated linear macromolecules with a paraffinic structure.”

They go on further to state that, “In addition to the base polymer, both EPDM and Butyl contain reinforcing carbon black, fillers, process chemicals, antioxidants and vulcanising agents.

After mixing the ingredients into a homogenous plastic compound, two layers of the rubber are rolled out in a calender to form a double sheet. Vulcanisation is then carried out. The long rubber molecules in the material are cross-linked through heat and pressure, creating an elastic membrane.”

In the past, it is the use of these fillers that has compromised the quality of some of the products available from more unscrupulous dealers. Hopefully these are now long gone, but to avoid dissappointment stick to a reliable manufacturer and a dealer that can tell you difference between the two products.

As far as their performance or longevity is concerned, you will find that EPDM is sold at a slightly greater thickness to a butyl product of corresponding performance or guarantee. Neither are affected by varying temperatures or the environment (sunlight, ice or rain). They are both chemically stable and always returns to its original dimensions after stretching. Although EPDM in the dark days of the past may not have been and it is not quite as malleable and stretchy as butyl. For very angular formal shapes, butyl is easier to fold into corners and around sharp bends, but for informal natural profiles, EPDM seems to iron itself to curves with the minimum of unsightly folds.

Site Map copyright 2010