Build a pond without a liner: clay, bentonite, a shell or concrete - the 5 solutions compared honestly

Don't want plastic in the garden, have clay soil that seems to retain water, or simply want a pond “like in the old days”: there are many, often very legitimate reasons for wanting a liner-free pond. The good news is that it's possible. The less good news is that each solution has strict conditions, and a failed clay pond can drain away within a few summer weeks.

Comparison table

1. The preformed shell

This is the most common answer to the question “without a liner.” Fiberglass-reinforced polyester shells are rigid, durable, and repairable. They often include shelves for plants. The key to success is backfilling: an even bed of sand beneath the shell, and backfilling with moistened sand in layers, filling with water at the same rate to balance the pressure.

2. Puddled clay

This is the traditional technique used for farm ponds and watering troughs: a layer of kneaded wet clay, then compacted in successive layers, forms a watertight bottom. It only works if you have truly heavy clay, low in sand and stones. A simple test: a ball of wet clay should be able to be rolled into a thin coil without cracking.

• Thickness: several tens of centimeters, compacted in layers.
• Gentle slopes, because clay slides on steep slopes.
• Clay must never be allowed to dry out: once cracked, it does not become watertight again on its own. Fill it as soon as the work is complete.
• Protect the bottom from tree roots and avoid trampling the banks.

3. Bentonite

Bentonite is a clay rich in montmorillonite that swells considerably on contact with water and seals the soil pores. It is used as a powder, mixed with the soil at the bottom, or in the form of bentonite geosynthetic clay liners unrolled like a liner and then covered with soil. These mats are commonly used in ecological engineering for ponds and retention basins. They require careful installation, with overlaps and sufficient soil cover.

4. Water-table pond

In a valley bottom or a wet meadow, sometimes all you need to do is dig below the water table to create a pond. This is the most natural of all, but its level follows that of the water table: high in winter, sometimes almost dry at the end of summer. Excellent for amphibians and dragonflies, unsuitable for ornamental fish. Before digging, inspect a test hole at the end of summer: this is when the water table is at its lowest.

5. Concrete

For a pond with straight lines, reinforced concrete is the natural structure. But it is not watertight on its own: a suitable waterproofing treatment is required, and the cement makes the water highly alkaline for several weeks. Before introducing fish, check the pH for several consecutive days.

Building a pond without a liner

In a clay pond, plants are installed directly in the bottom, which is one of the major advantages of this technique. In a shell, planting baskets placed on the shelves are used.

Read also

For a pond designed to support biodiversity: How to create a natural pond to promote biodiversity in your garden?.

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Frequently asked questions

— Is clay soil alone enough to build a pond?

Rarely as is. Simply clayey soil often lets water escape through sandy seams, roots and burrows. It requires rich clay, kneaded and compacted into a thick layer.

— Can fish be put in a clay pond?

A few native fish can live in it, but koi and goldfish rummage through the bottom, constantly cloud the water and can damage the clay layer.

— How long does a preformed shell last?

A properly installed polyester shell lasts for several decades. Thin plastic shells age faster in the sun.

— Which solution is the most eco-friendly?

A groundwater-fed pond and a pond made with local clay, when the terrain is suitable. Otherwise, a quality EPDM liner remains a durable and inert solution, often more reliable than the alternatives.

In summary

• Preformed shell: the simplest and safest liner-free solution.
• Puddled clay and bentonite: for natural ponds, requiring careful installation.
• Groundwater-fed pond: only if the water table remains high in summer.
• Concrete: formal ponds, with waterproofing and pH control.

Last updated: 28 September 2026.