Cultured Stone on Wiki (I am a link; you can click me)
I’m not a rock guy by any measure of the idea… so, am I working with ‘cultured stone’ here? This is a common “Hill Country Limestone” product you’re seeing on my chimney photos.
[quote]Today, cast stone is a Portland cement-based architectural precast concrete product manufactured using high quality fine and coarse aggregate as its primary constituents. Simulated stone, or look-alike products made with alternative ingredients such as gypsum, lightweight products, glass fiber, calcium silicate, stucco and other materials are less durable and not nearly as well time-tested. The use of a high percentage of fine aggregate creates a very smooth, consistent texture for the building elements being cast, resembling natural cut stone. Other ingredients such as chemical admixtures, pozzolans, and pigments also may be added.
Cast stone frequently is produced with a low water-to-cement ratio mixture with a “dry” (or “earth moist”) consistency. The mixture is consolidated into a mould using an air-driven tamping device or vibration under pressure, which is much like the formation of natural sedimentary rock. Products manufactured in this manner are referred to as vibrant-dry-tamped (VDT) cast stone. For cast stone mixtures produced with a slumpable consistency mixture, the concrete typically is consolidated using internal or external vibration applied to the production mould.
Over the last decade, new types of admixtures have been developed for VDT concrete products. These new admixtures do not normally work with “wet cast” concrete. These new plasticizers are more efficient than using air-entraining agents to increase compaction in VDT concrete. Some plasticizers have chemical properties that react with the cement to increase ultimate strengths of semi-dry concrete. Another important type of admixture for VDT concrete is integral waterproofing formulas. Tests have shown that some of these integral waterproofing admixtures have improved strength by as much as 20% while reducing the absorption by 40%. The increased strength and reduced absorption results in improved freeze/thaw durability.[/quote]