There are basically two processes for creating cast stone. The oldest version is referred to as Wet Casting. This method calls for the construction of a reverse mold of the required unit. This mold is later filled with a wet mix of cement and aggregate and then left to set for a day. Thus, the yield produced by this method is one piece per mold per day.
The second type of casting is called Dry Casting. Dry casting and relies on similar methods as Wet Casting, however, the mix used is made as dry as possible and therefore the mix must be compacted into the mold consistently. The advantage, here, is that the mold can be removed from the casting immediately after the compaction cycle. This allows increased production per day per mold. This process is preferred by cast stone producers because of the increased yield and the limited up front cost of the mold.
Dry casting then requires the newly formed casting to immediately enter a hydration chamber with an ambient temperature in excess of 70 degrees F. This additional step must take place because the dry mix used to start the casting does not contain enough water to facilitate proper hydration of the cement or to start the crystallization/bonding process of the cement to the aggregate.
After the casting has been in the hydration chamber for a day, the units are washed and stacked for storage. The castings must sit undisturbed for a period of at least twenty-eight days to maintain a proper cure cycle and achieve the required 6500 psi compressive strength.
Dry casting produces a unit that cannot include any reinforcing within the casting. This effectively eliminates the ability to use the castings a structural units in the project. It also is a factor in limiting the length of the castings to generally twenty four inches.
Wet casting can include reinforcing. However, the placement of the reinforcing within the casting must be exact and contained well within the unit. Any close proximity to the surface may produce exfoliation of the reinforcing and thus subjecting the casting to failure through internal rupture.