actually I used aragonite sand. Since aragonite is calcium carbonate, it formed a stronger bond as the glue chemical reacted with the aragonite.I used this on my rockwork for my upcoming tank. I've used a few different products over the last few years and this one was by far the easiest. I was hesitant that maybe I had to use marco rock and ground up rocks I used a fine grade sand for the joints and it worked extremely well.
Edit: gloves are a must!
the rock breaks well before the bond does.