Bentonite that is mixed too fast stays lumpy, and lumps do not build a filter cake. The bore wall then loses fluid, the pump works harder and the reamer runs dry. The fix is not a different product. It is the order and the time you give it.

Why the mixing order matters

Bentonite needs free water to hydrate. If polymer is already in the tank, it coats the clay particles before they can swell. The result is a thin fluid that looks fine in the tank and fails in the bore. So: water first, polymer second, bentonite last.

How much bentonite

Start at 40 kg per 1,000 litres for sand and 25 kg for clay. Measure the viscosity with a Marsh funnel after hydration, not straight after mixing. A reading of 40 to 45 seconds suits most pilot bores.

Hydration time

Give the mix at least 15 minutes in the tank before you pump it. In water below 10 degrees Celsius, double that. A MudForce 2500 circulates the tank in about three minutes, so 15 minutes means five full passes through the venturi.

Setting up the venturi

  • Keep the hopper half full so the venturi pulls a steady stream of powder
  • Watch the vacuum gauge: a drop means the nozzle is clogging
  • Flush the hopper and the line after every batch, before the bentonite sets

Quick reference

Ground Bentonite per 1,000 l Marsh funnel
Sand 40 kg 45 to 55 s
Clay 25 kg 35 to 40 s
Cobbles 50 kg plus polymer 55 to 70 s

These are starting points. The return flow tells you within an hour whether the mix is right: clear returns mean the cake holds, muddy returns mean it does not.