How to Build Rock Waterfalls Using Black Pond Foam

Updated February 21, 2017

Building rock waterfalls in your own backyard can be tricky if you do not have the right materials. Rocks can slip out of position and damage the hardware or knock dirt into your pond. Building these rock waterfalls using expanding black pond foam can solve these problems. This material, non-toxic to fish and plants, will hold rocks in place and create a more realistic-looking watercourse.

Construct a pond for the waterfall to run into by digging a hole in the ground and lining it with a flexible pond liner. The hole should be at least 2 feet deep at the deepest point and have no rocks or roots in it. The liner must rest directly on the ground so it is not stretched or damaged. Edge the pond with rocks to hold the liner down and make it look more natural.

Place a submersible pond pump in the bottom of the pond hole. Attach a long hose or tubing to the water outlet port. This hose must be long enough to reach the other end of the waterfall structure you intend to build.

Place several large rocks next to the pond to form the base of the waterfall. Put on gloves, then squeeze expanding pond foam between these rocks to fill the spaces. Also put a thick bead of the foam on top of the base rocks.

Lay another layer of rocks over the base layer, much as if you were building a wall. Concentrate on making a natural-looking waterfall structure instead of a rectangular tower. The rocks should mostly support themselves, as building a rock waterfall with foam is not as secure as using concrete.

Position the hose from the pond pump so it stretches up the rock waterfall structure. The end of the hose must point down toward the pond so the water will flow in the correct direction. Hold this in place with a flat rock laid over the top.

Spray a liberal application of foam between and over the surface of the rocks where the water will flow down. Working quickly before the foam dries, lay the finishing rocks on top of the solid foam watercourse. These rocks can be small ones designed to make the rock waterfall look natural, or wide, flat rocks used as tiers for the water to cascade over. Allow to dry for at least 24 hours.

Fill the pond with water after the foam is dry and turn on the submersible pump. Check the waterfall for leaks or places where the water runs in the wrong direction. Turn the water off again and allow the structure to dry thoroughly before adding more black pond foam to seal holes or build up edges to hold the water on course.


Pond foam is very sticky. Always wear gloves. Other expanding foam can be toxic to fish and plants. Use foam rated for ponds only.

Things You'll Need

  • Waterfall pump
  • Hose or tubing
  • Rocks
  • Black pond foam
  • Utility knife
  • Gloves
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