Sodium Bentonite Clay Powder - Bentonex SB - Civil Engineering Grade - Pottery - Pond Sealer

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10x25kg £292.91 £351.49
20x25kg £446.24 £535.49
42x25kg £602.91 £723.49
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Sodium Bentonite powder - Bentonex SB

Sodium Bentonite is used in foundry, metallurgy, well drilling slurry, oil, agriculture. Bentonite is also used in chemical industry, environmental protection, zoology construction, ecological construction, building, paper making, textile. Bentonite also can be used in printing & dyeing, ceramics etc. This clay is Engineering grade and suitable for use in engineering projects. It is commonly used for sealing ponds, lakes, landfill sites, lagoons etc (see below). 

Sodium Bentonite is not recommended for cosmetic applications. 


properties of Bentonite Clay:

  • CAS No: 1302-78-9
  • EC No: 215-288-5
  • Other names: sodium Bentonite, Montmorillonite, Aluminosilicate of sodium
  • Appearance: solid powder
  • Colour: Tan
  • Odour: mild
  • Bulk Density: 800 – 900 Kg/m3

When bentonite is mixed with water, the water molecules will enter between the clay plates, forcing them apart. While the plates are dispersed, the bentonite slurry becomes quite fluid. However, on standing the particles become oriented with the negative surfaces of the plates being attracted to the positive edges. Viscosity increases and a gel is formed – a reversible effect known as thixotropy.

A typical empirical formula for bentonite is:

(Al, Fe0.67 Mg0.33) Si4O10(OH)2Na,Ca0.33



  • Sealing ponds, lakes and landfills (more information below)
  • Making Green Sand for sand casting aluminium (used between 5 and 11% mixed with sand and water)
  • Well drilling slurry.
  • Used as a binding agent in iron ore production.


Bentonite For Sealing Ponds:

Sodium Bentonite clay swells up to eighteen times its dry size when it becomes wet. Expanded bentonite forms an impermeable gel seal which makes an excellent pond sealant. Bentonite is environmentally safe and does not affect the water, livestock, or wildlife. When properly applied, it will not harm fish. For these qualities, bentonite also makes an excellent liner for new pond construction.

When sealing a leaking pond to prevent water loss through seepage, Bentonite powder can be applied directly to the soil in the pond bottom or it can be sprinkled on the surface of the water and allowed to settle to the bottom. This method is best suited to shallow ponds and not deeper ponds, where the granular bentonite is better.

There are three basic methods: the blanket method, the mixed blanket method and the sprinkle method. Bentonite is easily applied. In the case of small ponds, it can be applied with simple hand tools and for larger ponds, with ordinary farm equipment.


Click here for further information on how to apply bentonite:


Application Rates:
  • Clay soils: 5-7 Kg/m2
  • Sandy Silt: 10-12 Kg/m2
  • Silty Sand: 12-15 Kg/m2
  • Clean Sand: 15-20 Kg/m2
  • Rock or Gravel: 20/25 Kg/m2



• Since bentonite powder is a dusty and highly absorbent mineral, we suggest carrying out the work on a calm and dry day. The use of goggles, dust mask, and gloves is recommended.
• Remove any large lumps and stones from the soil, which needs to be sufficiently dry to mix easily with the bentonite powder.
• In the case of very porous soils (such as those with a high content of stone, limestone, chalk or peat) we suggest using a bentonite enriched sand layer. Suitable fine sand for mixing is readily available from builders’ merchants.
• To achieve a good seal, the bentonite powder must be thoroughly mixed with the soil or sand.
• Mixing can be carried out by use of a cement mixer. Add the soil or sand first, followed by the bentonite.
• For sandy soils, porous soils and bentonite enriched sands we suggest using 10 Kg of bentonite per square metre. For clayey soils, as little as 4 kg per square metre may be adequate.
• The bulk density of bentonite powder is around 850 Kg /m3. This is much lower than soil or sand, so it is advisable to weigh the first shovels or buckets to ensure that the desired ratio is being used. (Typically, sands have a bulk density of around 1600 Kg/m3).
• Mix the bentonite with the soil or sand until a uniform colour is achieved. Take a sample to see if the bentonite is binding the soil (or sand) by squeezing a handful. If the mix is dry and powdery, add some water to achieve swelling and bonding. If the mix is sticky, too much water is present and more soil, sand or bentonite should be added.
• Lay the prepared mixture over the area of the proposed pond site and rake to obtain an even layer. Once it has been tamped hard or firmly compacted with a heavy roller, the mixture should form a dense layer of 20 to 25cm in depth. The harder the soil is packed the lower will be its permeability and the better its long term resistance to the passage of water. Hard rammed bentonite enriched soil will have a density of approximately 1.5 tonnes per cubic metre.
• Apply a top layer of 5 to 10cms of soil. This should also be compacted by tamping or heavy rolling. The bentonite and soil (or sand) mixture is now trapped as the middle layer of a sandwich, and the bentonite cannot leak out.
• Ideally, the sides of the pond should not have a gradient exceeding 1 in 3 otherwise slippage can occur during preparation or during the life of the pond, leading to water loss at the perimeter.
• Remember it may be necessary to top-up the water from time to time to offset evaporation losses during warm weather.
• Our guidelines are offered in good faith but total success cannot be guaranteed. The movement of worms and the roots of aquatic plants may puncture the bentonite enriched seal.

Download file for Pond & lake Construction Guidelines


Click here for MSDS

Click here for the Specification sheet


PLEASE NOTE: This product is not for human or animal consumption.