<a href=showthread.php?s=&postid=9692953#post9692953 target=_blank>Originally posted</a> by Yinepu
I will be making some rocks this weekend.. so I'll be sure to post my recipe and what all I do as well as any results!
I already have the Portland cement type I/II
play sand
crushed oyster shell
crushed coral
still need to get some salt...
Yinepu,
I've built rock several different ways now since joining up with this group.
My favorite recipe uses a mortar mix instead of pure Portland cement. A mortar mix has a pre-measured volume of sand already blended in (for the needed aggregate function). Menards sells a mortar mix that is rather light in color (more so than most of them, IMO).
In a clean 5 gallon poly bucket, I measure out a volume of this mortar mix, then get it wet enough with clean tap water to work with (about like dry cottage cheese). Once I get these two ingredients thoroughly blended, I add an equal volume of rock salt (Mortons in the blue bag) and thoroughly incorporate it into the mix. Then I pour my aggregate into moulds that I create in plastic bus tubs (like the bus boys use in restaurants) that I've half-filled with damp crushed calcium poultry feed additive (looks like fine medium gray sand).
Once I get everything cast and the tools cleaned up, I cut open a poly garbage bag and drape it over the bus tub and secure the bag to the tub with a length of electrical or duct tape just under the lip of the tub. Then I let is set
undisturbed for seven full days!
(this is a very important step that many folks try to rush. If you try to rush this step, you will probably end up with broken rock)
Wrapping the tubs with poly garbage bags allows the cement to hydrate properly (in a moist environment) until it is strong enough to handle. After waiting 7 full days, I remove them from the moulds, brush them off, and gently set them in a Stearite poly tote container filled with fresh tap water.
For the first few days, I change the water daily. There will be a lot of different leachants on and around the rocks. I just swish them around in the water before dumping the water out and refilling with fresh water. After the first week in the water, I only change the water every week.
This water cure is when most of the pock marks and crevices develop in the rock as the water leaches out the rock salt the longer it sets in the water.
Once you think they may be getting down to a manageable pH range, remove them from the tote, thoroughly rinse out the tote, scrub and rinse the rock again, return them to the tote and fill it with fresh clean water. Let them set for a few days. Some drop a powerhead in there, but I don't since I do this all outside. After a few days swish the water around real good for a few minutes, then take a sample to test.
Once you get the pH in line, you're good to go. HTH!
Guy