For centuries, builders have sought the perfect wall finish. While traditional lime plaster holds historical significance, modern gypsum plaster has become the preferred choice for achieving exceptionally smooth surfaces. The fundamental reason lies in their distinct chemical compositions and physical behaviors during application and curing.

Gypsum plaster, primarily composed of calcium sulfate dihydrate, undergoes a controlled setting process. When mixed with water, it rehydrates and forms a dense matrix of interlocking crystals. This crystalline structure is inherently fine-grained, allowing it to fill minor imperfections seamlessly. The setting time is predictable and relatively fast, typically within a few hours. This allows finishers to work the material during a known "window of workability," polishing the surface to a high sheen with a steel trowel before it fully hardens. The minimal shrinkage of gypsum during drying further prevents the formation of fine cracks or a grainy texture, preserving the smoothness achieved during troweling.

In contrast, lime plaster, made from calcium hydroxide (slaked lime), sets through a completely different process: carbonation. It requires absorbing carbon dioxide from the air to slowly convert back to calcium carbonate. This process is notoriously slow, taking weeks or even months to fully cure. During this extended period, the surface remains vulnerable. It cannot be over-troweled or polished aggressively as it remains chemically active and soft. Attempting to do so can tear the surface. Furthermore, lime plaster shrinks considerably as it dries and carbonates, often necessitating the use of fibrous materials like hair in the mix to control cracking. This inherent shrinkage and the slower crystal formation often result in a final texture that, while beautiful and breathable, possesses a subtle, characteristic "tooth" or unevenness compared to the glass-like finish possible with gypsum.

The practical implications are clear. Gypsum plaster's rapid, predictable set and low shrinkage enable applicators to achieve a flawlessly level and smooth plane in a single coat, often ready for painting within days. Lime plaster, while excellent for historic restoration and moisture-buffering, typically requires multiple coats and extensive curing time, with a final texture that is more matte and irregular. For contemporary interiors where perfectly smooth walls are the standard, gypsum plaster's physical properties make it the superior technical choice for efficiency and finish quality.