Two to four liters of white glue are diluted and then mixed with each bag of sealant (22 kilograms ±). About three bags are required for a sixty cubic meter tank. Two bags should be sufficient for a second inside layer. This project is possible without the glue but occasional bonding problems may occur.
A white or colored first layer inside a water tank makes it easier to see a second grey layer but is not necessary for a good seal. The inside seal of colored open reservoirs or swimming pools starts with a first coat of grey, then a second color layer. Do not work too hard on colors in swimming pools as they will change over time.
The following paragraphs describe a multi-colored, single outer layer, to visually blend a water tank with the environment, for example. The same procedure is used to apply a second layer, which is timed for as soon as the first layer is sufficiently durable to be unaffected by broom bristles or other application tools (16 to 20 hours).
Mix the main batch of grey base in a paddle wheel plaster mixer. Separate approximately 1/4 into various buckets (for multiple colors). Lighter colors without red are mixed with a wand propeller on a drill motor in these buckets. (White base Thoroseal isn't quite right for rock colors but will make pastels, if desired).
The main color is then mixed in with the material still in the plaster mixer. (Finger paint on a hot muffler or something else hot to see a quick dry approximation of cured colors).
When the base color looks right, pour 1/4 to 1/3 of it into buckets. Now mix blacks, dark browns, and other dark colors with the electric drill motor and mixer attachment. (A stick will work but some colors resist mixing and turn into lumps, a few unmixed lumps burst under the broom or brush bristles and add interesting streak effects).
The color pallet now contains buckets of non-reds, a mixer loaded with base color, and additional buckets of darker colors, which were mixed on top of the base color.
Use kitchen measuring cups and other measuring containers. Take notes, write all colors and measurements on paper. File the notes in a safe place. Use standard colors if possible.
Schedule the work to begin application during late afternoon, approaching evening. A foggy or cloudy day is ideal. Pour some base color into a wheel barrow and begin working on the shady side of the tank or other structure. Dip the stiff bristle push broom in base color and begin the fun. Work both ways around structure toward the sunny side, hold off working on the roof until the sun is very low.
Use a mixing tray and a second push broom if there is a second base layer color. The mixing tray is placed near the wall and brooms are used in the same way to seal the inside. The large push broom quickly moves material up and out of the mixing tray and onto the wall. Use smaller hand brushes for other small volume colors and to work the material into rough spots.. (An occasional green or brown (etc) pure pigment in glue or dry should be experimented with here and there).
Return to the starting point and mist with water to keep the thin layer moist. Avoid rivulets of excess moisture which will wash away the newly applied material.
Pigments are best from barrels. These colors have names like "raw umber", "sienna" or other familiar artist's paint names.
Maintain moisture until the night becomes too dark to see. Return early in the morning and apply moisture until evening. Now the waterproof layer is permanent (at least for 30 ± years).
The finished water tank may show some minor leaking even after application of water seal layers on the inside and outside. Tank builders often refer to this as, "sweating." Do not worry about minor leaks. The water is moving so slowly that evaporation leaves minerals behind which gradually solidify into cement like material which eventually stops all moisture from escape and makes the tank totally water tight.
Note that the natural seal of evaporating water does not occur on outside rooftops. Rainwater rinses microscopic cracks clean rather than plugging them up with deposited minerals. A completely waterproof ferrocement roof can be accomplished during construction by fog misting the top and continuously using a stiff bristle broom on any shrink cracks until the plaster becomes too hard to effect with mist and broom.
A simple method of spraying the water seal and color layers is available for those who make a business of building ferrocement structures. Eighty Liter ± agricultural chemical mixing tanks are available. Tanks of this type have a wide mouth hatch for pouring in material and can be pressurized with compressed air, which pushes the thin sealing material through a garden hose. One person sprays the material on walls and ceiling while others spread it with push brooms and smaller brushes.
Expanded metal is a sufficiently fine screen for separating out lumps which might plug the sprayer. Pour mixed material through expanded metal to remove lumps before attempting to pressurize and send liquid through a 15 to 25 meter garden hose. A two centimeter diameter garden hose is sufficient if the plumbing bend out of the bottom of the pressure tank is 2.5 centimeters in diameter. Garden hose with a 2.5 centimeter diameter is available but not necessary. Run water through spray apparatus to clean tank and hose.
Spray material onto structure surfaces using the thumb on the end of the hose, just like spraying water on a garden. Wear a thin dish washing type glove to avoid abrasive wear on skin.
There are several commercial products to accomplish this job, many have official stamps of approval. The web caretaker knows of individuals who have used ferrocement tanks waterproofed as described since the 1960's, with no apparent problem.
continue to Chapter 11