Lining it all up
Once the hole has been thoroughly prepared, go ahead and install any in-ground equipment components you have, including skimmers, waterfall filters, or bottom drains. Spread the underlayment across the excavation and, starting from the deepest layers, press it into the contours of the pond. There should be excess all along the border of the pond - don’t trim it yet! If you must use multiple pieces to cover the pond, there’s no need to glue or attach them together - just lay them with a generous 12-inch overlap. Make absolutely sure you’re not leaving any inch of soil uncovered with the underlayment!
EPDM liners are great for their flexibility and durability, but they are the heaviest of the geotextile pond liners and you need to take care that no damage comes to the liner during installation. Your liner will come folded up and BTL Liners will provide clear instructions on how it should be unfolded to minimize the need to drag it around for adjustments. Depending on the size of your pond, find a team of volunteers to help with this stage. During unfolding, you’ll want to line them up along the edges of the liner and pull it out evenly to avoid any risk of tearing.
Once the liner is unfolded, start again at the bottom of the pond and use your feet to gently push the liner to match the contours of the pond. Do NOT stretch the liner. It should have plenty of slack and you can allow a few natural wrinkles and pleats as you adjust it. Again, you should have a 1 - 2-foot margin overlapping the ground around the pond. It’s still not time to trim it, but you do need to make sure the margin is wide enough to allow for secure anchoring. If you find the liner isn’t as stretchy as you expect, let it warm up in the sun for a bit before continuing.
Any plumbing elements that need to penetrate your liner should be connected and sealed now. Use a boot kit designed specifically for EPDM liners, which should offer a flange with adhesive backing for a waterproof seal. These kits can typically be cut to fit pipes with diameters ranging from 1 inch to more than 6 inches, and a stainless-steel work clamping ring will make a secure connection to the pipe.
If you have any large stones or decorative rocks you want to place in your pond, place them before you fill the pond and conditions get slippery. Use extreme caution to avoid dropping or dragging stones across the liner. In fact, you may want to lay out a section of excess underlayment where the stone will sit, trimming it closely to the base once it’s in place. That extra layer not only avoids damage as the rock is placed but provides additional cushioning for the liner over time.
Next, add river rocks or other decorative elements to your pond. Rinse rocks well before you carefully shovel them in and spread by hand. Again, the name of the game is protecting the liner. Rocks (and eventually plants) can hide wrinkles or pleats in the liner if you find them objectionable. Remember, though, that those wrinkles allow the liner to adjust over the years and accommodate for settling or tiny movements of the ground without putting it under undue stress.
It’s Starting to Look Like a Pond!
Enlist the help of a few volunteers, or even a whole team, depending on the size of your pond. Have them line up along the edges of the liner and pull evenly while unfolding and adjusting, to avoid any risk of tearing.
Once your underlayment is in place and your liner has been carefully spread out, it’s time to add water. You can add a few temporary stones around the overlap if you’re concerned about excess movement during the filling process, but if the contours have been carefully shaped, you should be good. The weight of the water will press down on the liner, flattening any wrinkles and pushing the liner even more closely to the contours of the excavation. As the water fills, keep an eye on any sharp corners - you may need to make a smooth fold, which will be held in place by the force of the water as the pond fills. Remove any temporary stones around the overlap as the pond fills further.
Anchors Aweigh!
Your final step in installing a pond liner is to make sure it stays exactly where it should be and to prevent water from running underneath the liner and causing serious problems like bubbling up. Some pond owners will opt for super-simple solutions like simply covering the edges of the liner with heavy stones and hoping for the best. That’s not a great method to use if you want to ensure you get the most attractive and longest life out of your liner.
One of the most effective methods to securely anchor your liner is to use an anchor trench. This type of trench keeps your liner securely in place and simultaneously prevents water from seeping underneath. A slightly simpler version is the anchor shelf. Both methods are illustrated, along with a helpful video on the BTL website.
Start by digging a trench around the perimeter of the pond, at least 12 inches outside the pond’s edge. The trench should be about 12 inches deep from the surrounding grade and about 12 inches wide. Pull the excess liner and underlayment across the border and tuck it into the trench, laying it across the bottom and running it up the opposite side. Once it’s laid out, go ahead and trim the excess so it doesn’t poke up above the ground on the far side of the trench, but let the underlayment extend beyond the liner by a few inches. Backfill the trench with soil and compress it or even mound it up slightly so it remains level as it settles. Cover the liner that passes over the border with several inches of dirt, sand, smooth gravel, or other filler that will help in anchoring, but also protect the exposed liner from damage and exposure to the elements.
