The nopal, much like the maguey, plays a pivotal role in the history of Mexico. Not only used as both food (1) and medicine both plants have a space in the creation legends of Mexico and both have multiple cultural usages.

1. for both humans and livestock

For many generations prior to the arrival of the Spanish the Mexican people made a durable and environmentally friendly limewash (1) using the slime (2) from opuntia cactus. This slime was not only used in limewash but was added to the mortar that held their temples and pyramids together. It also helped paint adhere more strongly to other surfaces. Paint created using the nopal has several unique properties. It is waterproof but has the ability to “breathe”, this helps prevent water build up as it allows the paint to “perspire” in a way that artificial paints do not. The paint is ultra-adherent and helps protect surfaces painted with it from cold, humidity and insect damage. It is also more environmentally friendly that plastic based paints.

1. limewash is made from limestone that’s been crushed, burned, and mixed with water to make a lime putty. The putty is aged and then thinned with water and coloured with natural pigments. Limewash creates surfaces that are mottled and matte with a chalky texture something like suede. It lends a depth and luminosity to flat walls. While limewash paint can be used for both interior and exterior masonry and drywall applications like plaster, brick, cement, and stucco, it’s best not to use it on wood or metal
2. this slime is known as “baba” en espanol. This slime is a mucilage that can also be found when cooking okra or mallow (Malva spp) leaves.

Dr. Lorena Vargas Rodríguez from the University of Guanajuato recommends that the Opuntia Spinulifera nopal is the best cactus for creating this paint.

Ingredients : to prepare 6 to 7 litres

• 1kg quicklime
• 4 litres water
• 4 large and fleshy nopal pads
• 1 cup salt (table salt is fine)
• Colouring Agent*

*the paint will be white in colour due to the quicklime. There are various oxides and pigments for colouring cement that can be added to the mix if you seek a different colour.

Method

1. Peel the thorns from the nopal (much as you would when making nopalitos). You will want to remove the thorns as you may need to get your hands into the mix later. 
2. Chop the nopal into small pieces and cover with 2 litres of the water.
3. Allow the mix to sit for 8-12 hours. This will release the baba (slime) from the nopal.
4. Mash the nopal (whilst still in the liquid) with a stick (like you’re muddling a big ass cocktail).
5. Strain the mixture. Use a strainer with largish holes as a fine mesh strainer will get blocked easily. This is where you may want to get your hands into the mix to help push it through the strainer. Cactus thorns in the mix would be a bad idea.
6. In a bucket place the other 2 litres of water and add the salt and lime. Mix well until the salt and lime are dissolved and incorporated together.
7. Add the strained nopal mix to the lime/water and mix well.
8. If you are colouring the mix then add the pigment now.

Let mix stand for 8-12 hours before use.

To Use.

• Mix well before using (like you would with any other can of house paint)
• Apply mixture to surface using a paint brush. A fine fibre brush may be needed if the surface being painted is highly porous.
• In most cases a single coat will suffice. If you need to apply a second coat wait until after the first has dried completely.

References

• http://institutoculturaldeleon.org.mx/icl/story/741/Pintura-verde-y-barata-con-baba-de-nopal#.X0w8hsgza71
• Medina-Torres, Luis & Brito-de la Fuente, Edmundo & Gomez-Aldapa, Carlos & Aragon-Piña, Antonio & Toro-Vazquez, Jorge. (2006). Structural characteristics of gels formed by mixtures of carrageenan and mucilage gum from Opuntia ficus indica. Carbohydrate Polymers. 299-309. 10.1016/j.carbpol.2005.04.022.
• Rodríguez, Lorena & Figueroa, Gabriela & Mendez, Carlos & Nieto, Antonio & García-Vieyra, M. & Rodríguez, Jesús. (2016). Physical properties of mucilage prickly pear. Acta Universitaria. 26. 8-11. 10.15174/au.2016.839.
• Tomás Jesús Madera-Santana, Lorena Vargas-Rodríguez, Carlos Alberto Núñez-Colín, Gerardo González-García, Vicente Peña-Caballero, José Alberto Núñez-Gastélum, Clemente Gallegos-Vázquez & Jesús Rubén Rodríguez-Núñez (2018) Mucilage from cladodes of Opuntia spinulifera Salm-Dyck: chemical, morphological, structural and thermal characterization, CyTA – Journal of Food, 16:1, 650-657, DOI: 10.1080/19476337.2018.1454988