My primary interest is tropical fish, but I’ve been reading the pond section, and this year decided to take the plunge and install a 2500-gallon garden pond. I will be using an EPDM liner and was told to secure the top edge with a thin concrete lip. I’ve gone through past issues of AFI, but haven’t found any mention of using cement to finish the liner edge. Could you offer some tips?
My advice is to skip the concrete. Perhaps it makes sense in warm climates — perhaps. But in a cold area like upstate New York that type of finishing will not last a single winter. Frost heaves will snap it into fragments, and within a few years the concrete edge will be reduced to rubble.
The concrete lip also negates two of the great advantages of liner ponds. First, liner ponds are easy to install. Even very large liner ponds can be built with the aid of a few friends and without special equipment (or great expense). Cementing the liner in place is a big job, and messy as well. A cement lip also raises problems of pH and alkalinity control. The cement must be sealed to prevent mineral leaching into the water.
Second, liner ponds have the wonderful quality of being easy to modify and reshape at will. I’ve lost count of the number of times I’ve altered my ponds’ designs over the past 10 years. Once you cement the liner edge in place, you can no longer modify the pond’s layout. And believe me, no one is ever satisfied with their first attempt at laying out a garden pond (or their tenth, for that matter). I also imagine you will find the cement lip less than attractive.
Instead, I recommend using field stone to build a layered edge. It provides a beautiful finished look, but one that can be completely removed in half an hour. It can be rearranged to accommodate sunken pots, pond ornaments and so on, and it moves with the frozen ground, so the liner is spared any stress and there is no cracking or breakage.
For a more formal look you can use patio blocks. Because most blocks are made from cement they should be sealed. In either case use two or three courses of blocks to cover the liner. Fold the last 6 inches or so between the top and middle course.