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How to Seal a Concrete Pond That Leaks (Step By Step)

How to Seal a Concrete Pond That Leaks (Step By Step)

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Many homeowners install concrete ponds because of their durability. Sure, concrete-lined ponds can stand the test of time compared to their earthen counterparts. However, it doesn’t mean that they’re impervious to leakage.

In fact, even a well-maintained concrete pond can develop cracks over time!

Another cause of leakage is poor construction on the contractor’s part, like plumbing issues.

If you’re suspecting a leak in your pond, you’ve come to the right place. In this article, we’ll show you how to seal a concrete pond that leaks. So, keep on reading!

Step 1: Identify the Source of the Leak

If you think there’s a leak in your pond, the first thing that you should do is examine it. While the filter is running, fill the pond to its standard level and mark it with duct tape.

Wait for 12 to 24 hours before measuring how much water the pond leaked.

Afterward, fill the pond again to its standard level, but this time, you have to deactivate the filter. Mark it with duct tape and wait between 12 to 24 hours to inspect the water level.

If the pond loses less water while the filter is deactivated, it means that the leak is on the plumbing’s vacuum side.

In contrast, if it loses more water while the filter is running, you can find the leak on your plumbing’s pressure side.

If the source of the leak is on the plumbing itself, it’s better to reach out for professional help as the job might be too complex for a DIY.

However, if the source of the leakage is a crack in the concrete, you can proceed to the next step.

Step 2: Gather the Tools and Materials

Sealing those cracks is doable and only requires a little elbow grease. Here are the materials and tools you need:

  • Water
  • Whole Milk
  • Muriatic acid
  • Baking soda
  • Epoxy-based paint
  • Patching compound
  • Concrete bonding agent
  • Caulk
  • Chisel
  • Goggles
  • Wire brush
  • Putty Knife
  • Plastic bucket
  • Rubber Gloves
  • Medicine dropper
  • Paintbrush or paint roller

Step 3: Locate the Crack

Once you’ve verified that it isn’t a plumbing problem, you can inspect your pond visually. If you see algae on the sides of the pond, scrape its walls with a wire brush. This way, the algae will fill up the cracks and make them easier to spot.

Alternatively, you can turn off the pond pump. Then, use a medicine dropper to drop about two drops of whole milk every 3 inches around the pond’s perimeter. The crack will draw in the milk so you’ll be able to see them.

If you haven’t located the crack using the previous methods, you can turn off the pump and let the pond leak until the water stops dropping. After that, you’ll be able to spot the cracks just above the waterline.

Step 4: Remove Aquatic Animals and Decorations

Once you’ve located the cracks, the next thing that you need to do is to drain the pond and prepare it for repair.

First, you have to remove fish, other aquatic animals, plants, and decorations. Temporarily put your fish and plants in a tank.

Remember to treat the water the same way you treat it in your pond for your aquatic pets.

Step 5: Chisel Loose Concrete From the Cracks

The next step is removing loose concrete or debris from the cracks.

In addition, you should chisel at least 1-2 inches of concrete around the perimeter of the cracks. This will give a large area to work with.

Step 6: Apply Concrete Bonding Agent and Patching Compound

After cleaning the cracks, grab a concrete bonding agent, like a Polyvinyl Acetate or PVA. Apply it around the outside of the cracks.

Then, using a caulking gun, fill the damaged area with a concrete patching compound. Make sure that you press the caulk into the cracks to fill them completely.

After that, use a putty knife to scrape away the excess.

Step 7: Prepare the Pond For Painting

Put on protective gear, such as goggles and rubber gloves. Then, fill a plastic bucket with muriatic acid and water.

Keep in mind that the water should fill two-thirds of the bucket. Pour the mixture over the surfaces of the pond.

Next, neutralize the acid by sprinkling baking soda over the acid and water mixture. Leave the pond to dry thoroughly for up to eight hours.

Once your concrete pond is dry, sweep any baking soda residue.

Step 8: Apply Epoxy-Based Paint to the Pond

After you’ve cleaned your pond, it’s time to apply epoxy-based paint on the repaired cracks with a paintbrush or roller.

By doing so, you’re sealing the cracks completely and covering up small hairline cracks that may have formed on the concrete pond.

After you’re done painting, leave the pond to dry.

Step 9: Refill Your Pond with Treated Water

Once the paint has dried thoroughly, you can now refill the pond with water. Treat the water like you normally do for your aquatic plants and fish.

After the water is treated and stabilized, you can now put your decorations back into the pond. Lastly, place your precious pets and plants back in.

Final Thoughts

There you have it; your ultimate guide on how to seal a concrete pond that leaks. Make sure to identify the source of the leak first.

After you’ve located the cracks, you need to remove your fish, plants, and decor from the pond. Then you can fill them with a concrete bonding agent and patching compound.

Then, to seal them, apply an epoxy-based paint. Once the pain is dry, you can refill your pond and place your fish and plants back in.

However, keep in mind that you’ll need to reach out for professional help if it’s a problem with the plumbing.


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