earthen plaster and has been used to augment lime plasters in both Mexico and the southwestern United States for hundreds of years. Cactus juice is extracted by immersing cut leaves in water for as long as two weeks. Effect on indoor climate In principle, all wall coverings have an effect on the room climate: vapour permeable coatings designed to be capillary conductive, allow the wall layers behind them to absorb moisture and release it again. Due to the property of clay plasters to absorb a lot of moisture (up to nine times more than gypsum), a climatic buffer is created on the wall, which absorbs moisture and releases it again when the air humidity is low. These properties distinguish clay plasters from so-called "film-forming" surfaces, such as emulsion and latex paints, which have little or no permeability to moisture in the layers below. The area of the plastered wall has the greatest influence on the ability of the clay plaster to act as a climatic buffer. The thickness of the clay layer is of secondary importance in indoor use, as more than 80% of the moisture is initially bound in the top two millimetres of the clay wall. Just 10 mm is important for the "climate buffer effect" in "normal living conditions" because thick plaster layers (> 20 mm) are too slow to react to the constantly changing room air humidity. Clay stores heat (depending on the amount installed), and due to its high specific heat capacity, clay walls are able to compensate for temperature fluctuations. Thermal conductivity 0.47...0.93 W/(m-K). Interior earthen plaster Pure earthen plaster (plaster without lime, cement, or emulsified asphalt) is applied to interior surfaces more frequently than exteriors. Before the plaster can be applied, it must have a surface to bind to. Many types of wire mesh may be used, such as expanded-metal lath, woven wire lath, or welded wire lath. Reed mats are another option. If the plaster is being applied to a smooth surface such as drywall or plywood, a mixture of sand and wheat paste may be painted on to the surface to create the texture needed for plaster to bond. The plaster is usually applied in three coats. The first layer of plaster is called a "scratch coat". A "comb" is used to scratch the surface horizontally or in a crisscross pattern to provide a key for the second layer. In the