Prickly pear cactus is used in making a highly effective water-proof paint for homes. The technique originated in Mexican rural areas and is probably pre-Columbian. It was mostly used in the 16th to 18th centuries for painting churches and convents and the smooth paint gave a shiny, silk-like finish if white of eggs were added to the mixture," says Ms. Barney de Cruz. The type of whitewashing is also excellent for henhouses and pig stables, because it acts as a germicide and sealer, which prevents the formation of bacteria and the nesting of insects. Stables, hen and rabbit houses should be whitewashed at least two times a year and also each time there is a change of inhabitants in such places, according to her. The waterproofing substance is made by adding water to chopped paddles of the cactus, lime and salt in the right proportions. About 100 litres of water is added to 20 chopped stems of the prickly pear cactus (with or without the spines). Chopped stems should be soaked in water for 24 to 48 hours. The mixture is then strained to remove the chopped stems, leaving only the slimy water. To this decanted fluid is added a mixture of about 20 kg of lime and 2 kg common salt. A thick white paint will form, and it is then used for painting, according to Ms. Barney de Cruz. "It is recommended that at least two coats of this paint should be applied within a minimal interval of 24 hours. This paint gives an intense white colour to any kind of wall. Painting ferro-cement structures with this special whitewash seals the cracks that may have formed in the setting of the cement. The waterproofing effect is 100 per cent," she points out. The whitewash also results in better lighting, as white reflects light in the inside of the buildings. The paint on the outside results in the reflection of sunlight and thus diminishes heat, according to her. "Waterproofing with this substance is very economical. http://tinyurl.com/2emed9