This is going to be in a journal style, so bare with me. I'll give you background first.
Of course, like many reefers, I was strapped for cash starting up this hobby. 300 lbs of live rock for my up and coming 125g was just too expensive. So, I did a little research and stumbled on the many versions of DIY Rock. From crushed coral to crushed oyster shell to PVC shavings to noodles. I've pretty much read it all. So, I went with a decision just to try it to see how it worked. I went through several batches.
First Batch
Well, since my first batch was a test run, I decided to just use crushed oyster shell and cement. Crushed Oyster Shell at Atwoods was about $8 for 40 lbs. Portland Cement Type One was $10 for about 90 lbs. I mixed it to a rather thick consistency of about 4 parts Crushed Oyster Shell to 1 part Portland Cement. I then would grab a small clump and toss it on a cookie sheet. I would take a second clump and toss it on the first. I then repeated the process until I found the size and shape I wanted. There were also some that I hand shaped to make little crevices, caves, and indentions. It didn't work out well, but that is why it was a test batch. I then took them and baked them in the oven at 250*F because I didn't want to wait for it to dry for 24 hours. It took a few hours to bake. I then plopped some of them in the back of the toilet and others in buckets and tubs. I let them cure until the pH was a steady 8.2-8.3 and took them out.
Here is my conclusion to the first batch of rocks
Pros: Easy to make. Very cheap. Moderately easy to form. Unique outward appearance. Solid strength
Cons: Thick. Heavy. Very dense. Rough and sharp. Able to cut and scrape.
Here is a Cost breakdown:
40lb bag of Crushed Oyster Shell - $8
90lb Bag of Portland Cement - $10
Total: About $0.21/lb
Here are some pictures of the first batch of rocks.
Free Form Rocks
Two Rocks with Flat Ends Put Together
All the Rocks
Rocks Put Together
....To be continued.....