Concrete is often portrayed as a permanent or nearly indestructible option for lining your pond. However, it’s not quite as durable or easy to use for pond lining as you might assume. Concrete has a number of drawbacks when used alone. If you decide that it’s necessary for your pond project, you’ll likely want a layer of geomembrane underneath the material to trap any water that seeps through the concrete. Concrete is the most expensive way to line a pond, so make sure it’s necessary before budgeting it as part of your project.
There’s a common misconception that concrete is naturally waterproof and impermeable on its own. Yet, this material is far more porous than you might think. Much like a sponge, the tiny pores in the concrete create a capillary action that slowly sucks moisture from one side to the other. This can cause water to seep out of the pond, or into it, depending on the soil conditions and the thickness of the concrete layer. Adding a layer of flexible liner under the concrete stops this action from affecting the pond.
Development of Cracks
It’s true that concrete is very durable and strong against certain types of forces. But when concrete is exposed to tension rather than compression, it cracks easily. Soil movement, and settling underneath a concrete lined pond, eventually leads to tiny cracks forming in the material. It’s often hard to see these cracks, making them impossible to locate and seal for an impermeable liner. Concrete can crack within months or years of installation, slowly increasing the water lost to leaks over time. As with porosity, the best way to prevent and control these leaks is to add a layer of geomembrane from BTL Liners under the concrete.
Concrete is not safe for fish in its freshly cured state. The material releases damaging residues when first filled with water. It’s necessary to fill and drain a concrete lined pond at least three to four times before fish are added. If you’re in a hurry, a flexible liner will allow for immediate use of a new pond rather than a waiting period of multiple weeks as you drain and refill thousands of gallons of water. Applying fish-safe sealants can speed up the use of a concrete lined fishpond, but only to a certain extent.
Whether you decide to add concrete lining to your pond or not, you should start with a layer of flexible pond liner first. Fish safe AquaArmor from BTL Liners works equally well as an underlayment for concrete lining or as it does as a solo liner for ponds with challenging conditions.