Yellowstar Bentonite Grounding and Earthing Mixture (GEM)

Yellowstar Bentonite (Pty) Ltd. supplies a calcium bentonite and activated bentonite that quickly absorbs water and retains it for a long time. Yellowstar Bentonite contains in excess of 65% smectite content and a surface moisture of 7% and crystallographic moisture content of as much as a further 8%. Bentonite still contains moisture even when it looks dry.  It is used as an earthing back-fill and can be mixed with cement or the natural soil before being placed back in the holes dug for electrical and surge protection purposes.


Where electrical conductivity matters

In South Africa lightning strikes represent the single largest source of electrical shock that can affect electronics (such as surveillance cameras), structures (such as thatched roof homes and recreational areas). The following map shows where in South Africa this must matter to you.



How bentonite works

Bentonite can be applied in its ‘as mined’ form (ROM), in granular form and in fine powder form. Since bentonite has moisture inherently in it, even what appears to be dry bentonite still contains as much as 8% crystallographic water. Bentonite will require heat of 600oC-800oC to remove this crystallographic water, a temperature not easily found in nature.

By applying bentonite to the backfill, you will lower the soil resistivity. Calcium bentonite has Ca2+ ions and sodium bentonite have Na1+ ions. Sodium therefore performs better than Calcium bentonite. To offset this, activation of calcium bentonite is a common method used to increase the Na1+ ions available.


When to apply Grounding Bentonite

Electrical grounding must take place as soon as possible. There may be a reluctance to use bentonite grounding mixtures in wet season. Our advice is to use bentonite immediately. Research has found that the immediate performance of the mixture was not at his highest but improved over time. Bentonite could take 6-12 months to reach maximum grounding performance. Keep this in mind when planning.


How to apply Grounding Bentonite

Bentonite can be applied in its as mined form or in a fine powder form. At this early stage be reminded that in powder form additional dust protecting PPE is required. Furthermore, work on wind-still days or when there is a gentle breeze only. Our clients have used Yellowstar Bentonite at their projects in the solar farm projects of the Northern Cape as well as engineering projects around Gauteng. Our clients have used Yellowstar Bentonite at their projects in the solar farm projects of the Northern Cape as well as engineering projects around Gauteng.

All other forms of bentonite (ROM) or granular, can be mixed with cement (30% is standard) and allowed to mix. A cement mixer has been used by some of our clients when using the ROM bentonite.

Vertical holes: Consider using fine powdered bentonite

Horizontal trenches: Consider using coarse ‘as mined’ bentonite

There are various mix formulae but one which we recommend for a cable trench is follows:

7 parts Bentonite

1 part water

2 parts sand

1 part cement

Mechanical Mixing First mix bentonite with water. When mixed then add sand followed by cement.

Manual Mixing First mix the sand and water. When mixed then add bentonite followed by cement

Contact us and tell us what worked for you.



Compactable: Yes

Cost effective: Yes

Does not leach over time: Yes

Inert: Yes

Low Resistivity: Yes

Packaging: Coarse

ROM Fine: Milled

25kg bags: Yes

1-ton bulk bags: Yes

32-ton side-tippers: Yes No

32-ton pneumatic: No Yes


How much bentonite does one require for a specific project

The team at Yellowstar Bentonite can help you calculate the amount of bentonite required if you provide us with some basic information. Give us a call or send us an email.

Alternatively use one of the many trench fill calculators available online to get an estimate.


Where can I find out more?

You can follow some of these links and references in them to find out more about calcium bentonite as an earthing or grounding material.

Evert, C and Gijben, M (2017). Official South African Lightning Ground Flash Density Map 2006 to 2017. Earthing Africa Symposium and Expo 2017, Johannesburg, South Africa, June 5-9, 2017.


Lim, S.C. et al. (2013). Characterizing of Bentonite with Chemical, Physical and Electrical Perspectives for Improvement of Electrical Grounding Systems. Int. J. Electrochem. Sci., 8 (2013) 11429 – 11447


Lima, A.T. et al. (2010). Bentonite electrical conductivity: a model based on series–parallel transport. J Appl Electrochem (2010) 40:1061–1068