ENDURA HARD is a PATENTED amorphous colloidal silica solution designed to harden, densify and react with concrete better than lithium, sodium or potasium systems. Concrete has many pores. Our Endura Hard actually fills those microscopic pores with colloidal silica and "stacks" on top of itself creating an incredibly robust concrete surface to polish. This stuff is AMAZING! Try it today and see the immediate difference that this product makes in your polishing life.