Slaked lime — also known as hydrated lime, caustic lime, builders' lime, cal, or pickling lime, refers to the chemical compound calcium hydroxide (Ca(OH)2). It is obtained by mixing water with quicklime (unslaked lime), a process called hydration.

Slaked lime exists in the form of colourless crystals or a white powder. When water is added to quicklime, an exothermic reaction occurs, releasing heat and resulting in the formation of slaked lime. The reaction can be represented by the following equation:

CaO + H2O → Ca(OH)2

The addition of water to quicklime causes the chemical compound to undergo hydration, where calcium oxide (CaO) combines with water molecules to form calcium hydroxide (Ca(OH)2). This process is accompanied by a significant increase in volume, as the calcium oxide absorbs water and transforms into a solid.

Slaked lime is commonly used in the preparation of mortar and plaster. The addition of slaked lime to mixtures provides improved workability, plasticity, and cohesion, enhancing the overall quality and performance of the construction materials.