A place near New Orleans, La called Coral Connection makes their own Live Rock using the following. White Portland Cement, crush coral, and acrylic shavings. They sell it for $2.50 per pound. So, do the math if you needed 100lbs.
I couldn't find the white so I tried the gray. After making some rock about a month goes by and fresh water changes everyday, PH is still at or above 8.8 (PH strips on went that high). Frustrated, I wanted to try white Portland.
With that said, I went out to my local building supply store to buy my white Portland cement. It took for ever to find this but at 16 bucks for 92lbs, I'm not complaining. So, I made me three large pieces, using 2 parts crushed oyster shell, 1 part WHITE Portland cement, and 1 part salt rock. I rinsed the rocks with fresh water until the salt rock melted. Formed it and let it stand for about 24hrs.
During my water change in my tank, I put the old salt-water in a large plastic tote bin, with some of my sand from the tank, a small piece of seeded rock from my tank, a 10k 30" PC
light and a power head. The rock has been in the water for about a week and I tested the PH with test strips, which according to the color chart the PH is between 7.8-8.4. (color is in between)
Coraline is seeding on this rock that I made and the white looks more appealing than the gray. I don't know why the cure time was short; maybe to do something with the white cement? Just wanted to share my experience.