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500Grams of Bentonite Clay is sufficient to make 5Kg of new greensand

(Used to make Green sand for moulding and to recondition old sand)

What is bentonite?        What is the formulae for making greensand?
The ionic (chemical bonding) surface of bentonite has a useful property in making a sticky coating on sand grains. When a small proportion of finely ground bentonite clay is added to hard sand and wetted, the clay binds the sand particles into a moldable aggregate known as greensand  used for making molds in sand casting  Some river deltas naturally deposit just such a blend of such clay silt and sand, creating a natural source of excellent molding sand that was critical to ancient metalworking technology. Examples of this being Mansfield and Bromsgrove greensands. Modern chemical processes to modify the ionic surface of bentonite greatly intensify this stickiness, resulting in remarkably dough-like yet strong casting sand mixes that stand up to molten metal temperatures.
Making greensand
Green sand is not green in colour, but "green" in the sense that is used in a wet state (akin to green wood) There are various formulaes for this which can be found online which are very similar but this is the one I have used. You must ensure a thorough dry mix before adding the water.

  1. 90% Fine Silica sand (dry as it makes the mixing of bentonite easier)
  2. 10% Bentonite
  3. Water  sufficient to make the sand and bentonite workable without being sticky when you squeeze it in your palm it should bond together and break cleanly

If working with cast iron you can add 3 to 5% of coal dust which will help gases escape and produces a smoother casting.
These percentages are not set in stone and you may wish to reduce the bentonite content. Too much bentonite will lead to poor venting of gases.
For large purchases please contact us for for pallet delivery charge.


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