A plain, flat concrete surface provides nothing more than a dull, untextured gray appearance that does anything but excite the senses. To spice up the walls of your concrete building, add texture with an application of stucco. Stuccoing a building involves spreading a thin layer of new concrete over the surface that you can then rough up to create a textured, personalized finish. You can make the final stucco surface as rough as you like, as long as you correctly apply the stucco.
Clean the concrete wall with a power washer to blast away dirt, mud, old paint and all surface contaminants. The concrete must be completely clean before it can accept a new stucco finish, or the imperfections will show through the stucco.
Inspect the wall surface to make sure it is completely firm and structurally sound. Do not apply new stucco if you are not sure the wall can handle the added weight. If you find any holes or cracks larger than 1/8-inch across, fill them in with concrete patch or epoxy. Allow all repair work to dry before continuing.
Cut 3/8-inch-thick wooden pieces to fit across the wall horizontally. Attach one of these pieces to the very top of the wall and one to the very bottom, using masonry nails or screws. These pieces will help ensure you get a flat, level application of stucco. If your wall is taller than 8 to 10 feet, install a wooden piece across the center as well to keep better track of your level.
Mist the surface of the wall with a hose to dampen, but not soak, the wall. The concrete should be damp but not dripping for optimal stucco application.
Put on construction gloves and goggles, as well as long sleeves, to protect yourself from the caustic cement. Pour 1 cubic foot of sand, one-third of a bag of cement and one-third of a bag of lime into a wheelbarrow. Add water and mix the contents until the cement mixture is the consistency of pudding. Add the water gradually so you can stop before the mixture becomes too runny.
Load your cement mixture onto a mason's hawk. Cut some of the mixture off, using a mason's trowel. Working from the bottom of the wall up, hold the trowel at a 45-degree angle to the wall and spread the stucco mixture onto the wall. Spread it in quick, sweeping motions until the area is filled to the top of the wooden screeds you installed early; this will give you a 3/8-inch-thick base layer of stucco. Try not to fuss with the stucco once it's on the wall; you will level it later. Continue to trowel until you have filled in the entire area between the wooden pieces.
Set a long, flat, straight piece of wood or metal vertically against the wall at one end. Walk across the area, dragging the straightedge across the wooden screed pieces to flatten any bumps in the stucco base coat. Walk back to your starting point as well to create a fully level surface.
Inspect the stucco. Use the trowel to fill in any gaps you created with the level and then repeat the process until the base coat is completely flat. When everything is flat, detach the wooden pieces from the wall. Use the trowel to fill in the gaps left by the wooden pieces, scraping with the side of the trowel to keep the new stucco flat with the old. Once the entire base coat is applied, allow the stucco to dry until the shine on the surface is gone but the stucco is still relatively malleable; the time this takes varies by climate.
Gently run a wooden or foam mason's float across the stucco surface in small circles or swirls. Working the stucco again after it has started to dry will reduce cracks and shrinking as the base coat of stucco cures. Allow the base coat to dry overnight before you continue.
Mix up another batch of stucco. You do not have to worry about screeds this time, as the final coat is only 1/8- to ¼-inch thick. Trowel the material onto the surface, using the same methods as before, working in a thin, even layer, until the base coat is completely covered by the top coat.
Roughen up the top coat of stucco with a stiff-bristle paintbrush. Work in swirls, lines or circles as you choose to create a rough finish to the stucco that matches your desired texture. Once you have the desired roughness, allow the material to dry undisturbed overnight.