How Sodium Bentonite Dam Sealing Works
Sodium bentonite is a natural clay that swells to several times its original volume when wet. In a suitable, properly prepared and compacted soil treatment, it can reduce seepage from dams and ponds.
How sodium bentonite seals dams
Hydrated bentonite helps reduce the permeability of the treated soil layer. The product specification sheet gives a typical swell index of 7 to 16 mL/2 g. This is a test value, not a dry-volume expansion ratio or a guarantee that a particular dam will seal.
Application rate and site assessment
Bentonite Pro’s recommended application rate is 30 kg/m². Confirm soil suitability, the cause of leakage and the installation method before ordering or starting work. This recommended rate is not a rate specified in the product sheet or a universal guarantee of sealing.
The NSW DPI guide, Leaking farm dams, describes generic installation methods. It is the source for the method, mixing-depth and cover guidance below, not for Bentonite Pro’s recommended 30 kg/m² rate.
Mixed blanket method
Empty and dry the dam, clear the treatment area of rocks and vegetation, and prepare the soil. For a mixed blanket on suitable light or loam soils, incorporate bentonite into the upper 150 to 200 mm of soil, then compact with a roller.
Pure blanket method
Empty and dry the dam and clear the treatment area. For a pure blanket on suitable heavier soils, spread bentonite over the prepared surface, cover with at least 100 mm of site soil, then compact the covered treatment with a roller. Increase the cover to at least 450 mm where stock have access. Protective cover goes on before roller compaction. Refill gently to avoid disturbing the treated surface.
Before choosing a method, the leaking dam triage check helps confirm whether a drained bentonite treatment suits your dam.
Can you treat a full dam?
Do not rely on adding bentonite to a full dam as an assured repair. The NSW DPI guide describes broadcasting over water as “at best hit and miss” and does not recommend it because success cannot be assured. Arrange a site assessment if the dam cannot be emptied. Slurry application and soil incorporation are not interchangeable techniques.
Quantity calculator
For preliminary ordering, multiply the total floor and wall area to be treated by 30 kg/m²:
- 200 m²: 6,000 kg (6 tonnes)
- 500 m²: 15,000 kg (15 tonnes)
- 1,000 m²: 30,000 kg (30 tonnes)
Divide the required mass by 1,200 kg and round up to whole bags. For 500 m², 15,000 kg equals 12.5 bags, so order at least 13 whole bags before an allowance. Adding a 5 to 10% allowance requires 14 whole bags. Confirm any site-specific allowance before ordering.
Bentonite Pro supplies sodium bentonite fines in 1.2 tonne bulk bags, delivered across NSW, VIC and QLD. Contact us for a site assessment and quantity recommendation.