Prickly Pear Background Info

Earthen Plaster and prickly pear cactus juice

The liquid from prickly pear cactus is one of the most common additives [to earthen plaster].[1][2]

According to some sources, it helps the plaster set and increases its stickiness or adhesion. Cactus juice also serves as a stabilizer in that it helps make earthen plasters more water resistant and more durable. It also prevents dusting.

Cactus juice can increase plaster’s workability and its ability to be formed into the desired shape. Workability depends on the water content, the shape and size distribution of its aggregate (aggregate can be rock, sand, natural fiber, etc.), the age of the plaster, and the amount of other natural binder(s) (natural binders are clay, lime, wheatpaste, cactus juice, etc.) Altering the water content, changing the aggregate mix, the age of the plaster, or changing the binders will increase or decrease the plaster’s workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the natural binder and aggregates start to separate), with the resulting plaster having reduced quality. The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low workability, which cannot be readily made more workable by addition of reasonable amounts of water or binder.
Cactus juice works well because it contains pectin, a water soluble long-chain carbohydrate that acts as the binding agent to increase the adhesion of an earthen plaster. Pectin is also responsible for increasing the water resistance of an 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.[3]

  1. ^ Cedar Rose. “Plasters & strawbale”.
  2. ^ Athena and Bill Steen. “The Straw Bale Earthen House”.
  3. ^ Guelberth, Cedar Rose; Dan Chiras (2003). The natural plaster book: earth, lime and gypsum plasters for natural homes. New Society Publishers.