If diatomaceous earth is 85% sodium silicate, could it be added to plaster of Paris, with water, to form a hard surface, with the benefit of the diatomaceous earth to act as an anti mold agent, for instance if making one's own coaster?

  • $\begingroup$ Yes. In fact, you can mix it with pure gypsum and water to create a hardened diatom surface. People make them into coasters all the time. I think the ration is 2:1 (de to gypsum) but I’d have to confirm that. I’ve been experimenting with making a custom drain board. I have a pretty absorbent hardened cement made from a slurry of Portland cement and Food grade de with bentonite clay. The silica is amorphous in the food grade vs calcined, but that combined with the already absorbent rapid cement (the ingredients are proprietary but I’m pretty sure they use DE in that mixture too) makes for a ver $\endgroup$
    – Tina
    Sep 27, 2022 at 4:13
  • $\begingroup$ From personal experience - the hardness of the plaster is markedly increased. Much more force required to drill a hole in it, or scratch it. No measurements, just using it around the house for general repairs. $\endgroup$
    – Mike
    Nov 20, 2022 at 14:11

1 Answer 1


Diatomaceous earth is 80-90% silica (SiO2), not sodium silicate Na2SiO3 (or polymers).

Diatomaceous earth could provide strength gain for portland cement concrete (if it doesn't increase the water content), but is an inert filler for plaster. It might improve the properties you want in the final product, but I am unaware of its use for improving specific characteristics.

There are better fillers for plaster and concrete.


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