1 part portland II cement ,.......4 parts argonite sand,...... 1 part crush coral or oyster shells.... u mix them all in a tub.. (make a perdy dry mix.. for it will be more porous then wet mix... get another tub.. fill it up with about 7'' of argonite sand..,.. shape sand to form a mold.. put " the fake rock mix" into the sand form.. cover .. mix over with more argonite sand.. wait till dry (1 or 2 days) then BAM!!!! u have your rock..... look up GARF and ther argocrete rock for mor info....