August 2023

Two common methods of manufacturing cast stone: Dry tamp method and wet cast process. Both of these methods create a simulated natural cut stone look. The most common finish for a dry tamp cast stone is limestone or sandstone while the wet cast method is capable of providing a wider array of possible finishes. Best way to describe Wet casting is like baking a cake. Where the tin is your mold and the concrete mix is the batter. Important considerations to wet casting: the current concrete mixture is essential and mold must be in perfect condition to prevent any leak in the mold which will cause discoloration and quality deterioration. The mold release is very important to prevent surface defect and to have the best surface finish results. Then cast stone must sit for so many hours to properly cure and strengthen before removing the molds. On the other hand, dry tamp use hand tampered method where the dry concrete mix is hand tampered into the mold. This method gives the cast stone more of a refined and detailed look of limestone/ sandstone finish. Dry casting has faster demold time, and mold can be use several times a day, no treatment is required afterwards to achieved the limestone look, and repairs after demolding is relatively easy. Dry tamp replicate a carved stone while wet cast looks like a molded product where details does now show as well as dry cast. Also, dry cast can only achieve limestone or sandstone texture and cannot create a smooth finish. Wet cast product is better when a structural product is needed and where bigger pieces need to span large opening.

Cast stone falls within that broad definition where some people use cast stone, pre cast, architectural pre cast interchangeably. The biggest difference between architectural precast concrete and cast stone according to W. N. Russell III, executive director of the Cast Stone Institute is that “cast stone isn’t permitted to contain bug holes or air voids and must have a fine-grained texture, which is normally achieved by acid etching.” Cast Stone is best suited as architectural and/or aesthetic uses with structural advantages of concrete since it can be reinforced.  Cast stone is made with highly fine and coarse aggregates such as limestone, marble, calcite, granite, quartz, natural sands, Portland cement and coloring pigments. Then pour into mold to achieve a dense texture, similar to natural cut stone. It is available in any color and can look like limestone, brownstone, bluestone, granite, slate, travertine or marble. It can match terra-cotta or brick and makes a perfect substitute for brick shapes. Cast Stone’s appearance is improved by weather, year after year.  Precast Concrete is best used in none visible areas, where the appearance of air voids and surface irregularities is not an important consideration. Precast concrete is ordinarily made combination of sand, dark color gravel, pebbles, rock, and cement. All of which is poured into a mold where gradation of aggregates is not so important. After several years of weathering, the dark aggregates will begin to show.  Architectural Precast Concrete is best suited for projects where the appearance is not important and is usually used in the form of large curtain wall panel units or large spandrel members. Large aggregates of various colors mixed with a wet slurry of sand and cement is use then poured into the mold. The surface has exposed the aggregates, resulting in a pebbly-with-voids type of finish.  Precast concrete is less costly to manufacture because aggregates cost less and no surface finishing is required. Due to weathering there is a definite advantage in using Cast Stone rather than precast concrete.

There are several factors to consider when choosing stone materials for new construction, remodel, restoration or repair/replacement. Budget, and Aesthetic look, are important factors to consider when choosing between natural stone or cast stone. Natural material is quarried and delivered to the site, while cast stone is a man-made material. Natural stones come with variations in color and grain pattern while cast stone can replicate natural stone it can also be versatile and have color and pattern consistency or customize.  Even though natural stones are relatively strong and durable, Cast stone is stronger, less brittle, and can have PSI versatility. The cast stone strength can be modified depending on the use and method of casting. Another major difference is the cost difference. Natural stone cost can significantly varies depending on market conditions, quarry location, contractor’s markup, and contractor relationship with the stone manufacturer that can make natural stone more expensive. While cast stone is typically more cost effective than natural stone, there are also factors that accounts for cast stone cost such as the number of molds that are required for each project. A new mold must be made each time a different shaped stone is cast. The type of mold use and the different type, thickness, and intricacy of cast stone can also add to the cost. There are also repair cost difference between cast stone and natural stones. For instance, natural stones can be difficult to repair or replace. Also, natural stone cannot be tinted to a desired shade and it is difficult to find another natural stone to match the existing natural stone. Whereas, cast stone repairs or replacement can be performed more easily and can also be easily fabricated with color or stained to the desired color shade. Ultimately the choice between natural and cast stone often comes down to the clients or customers preference and budget.