How to Make a Concrete Collar for a Koi Pond

Measure your koi pond’s shape, size and embankment parameters. Sketch out the dimensions of the pool to assess the amount of cement mix needed to create a collar around the pond. Drain the pond if you’re able to relocate the koi while working on the collar so you don’t traumatize or injure them.

Remove ornamental rock, vegetation and other aqua-scape features. Repair, shore up or remove sections of the pool's bank that show signs of erosion, deterioration or are otherwise compromised. Dig a trench surrounding the periphery of your koi pond with a shovel so the concrete collar you install extends to a depth that’s below the pool’s waterline.

Build a framework for the collar that’s deep enough to fill the trench plus at least 8-inches more to form the collar. Use standard 2-by-4s if you’re a fan of old-school cement framing techniques or lengths of melamine plus clamps to hold the frame together. Choose a melamine frame over wood and receive a bonus: malleable materials allow you to contour the collar shape to curves running around embankments.

Seat the collar framework/mold into both sides of the trench, making sure the ground is flat in the center. Work the trench in sections if your koi pond is extremely large and you want to reuse sections of the frame, understanding that this will add time to the project since each segment requires maximum cure time before you move on to the next section.

Spray the interior walls of the framework with a silicone product so it’s easier to extract the framework after the cement cures. Mix and pour cement into the trench. Use a trowel to even out the top of the collar so it’s flat and uniform. Allow the cement to cure for up to 48 hours if the mix package doesn’t specify a recommended cure time. Remove the frames.

Plant ground cover that's known for putting down roots to shore up soil surrounding water, thereby adding a second line of defense around your newly-installed koi-pond collar. Arrange rocks around the periphery plus plants and/or a waterfall feature to complete the aesthetic remake. Return the koi to the pond if they’ve been on vacation.