Stucco, also known as Portland cement plaster, is a surface coating made of Portland cement, sand and sometimes a plasticizing agent like lime. Since stucco can be colored with mortar colorants and textured with a variety of tools, it is an ideal medium for dressing up a drab concrete block wall. It can also be applied to a wooden surface provided that building felt and wire mesh are mounted to the substrate beforehand.
There are only a few materials needed for making stucco: a bag of Portland cement and a bag of silica sand, and perhaps some liquid concrete bonding adhesive. You can also buy liquid mortar colorant if you would like a green-, red-, buff-, rose- or cream-colored wall.You'll also need a few basic tools for mixing and applying the stucco. For mixing, get a five-gallon bucket and hand mixer. Mixing stucco is hard work, but you can make it less of a chore if you use a 1/2-inch electric drill and a power mixing attachment. (Do not use a 3/8-inch drill for this chore; the motor may burn out under the heavy load.) You'll need a cement trowel for applying the stucco, a rubber float for smoothing it and a gardener's trowel for scooping it from the mixing bucket.
In general, stucco will adhere well to new concrete walls because the surface has an open texture that quickly draws the stucco into the minute pores of the concrete. Surface preparation consists of dampening, but not saturating, the wall with a fine water spray. You must keep the surface damp while working unless you use a liquid bonding agent.
Older surfaces may need more work, particularly if they are painted. First scrape the wall with a wire brush to remove any loose dirt or paint. Next spray the wall with a fine water mist. If the water is readily absorbed, then it's likely that the stucco will form a good bond with the surface. If droplets form and the water runs down the wall, the surface is probably inadequate for a good bond.
Here it's best to apply a liquid bonding agent before attempting to stucco the wall. In extreme cases, it may be necessary to have the wall sandblasted to expose a more porous surface. Another alternative is to mount waterproof felt and metal lath.
Pick a mild day to work and avoid days with high humidity because the excessive moisture in the air can extend the drying time of the stucco. It's also best to avoid hot, sunny days. The heat will cause the stucco to dry prematurely, shrink and develop hairline cracks. If the cracks do develop, they can be filled by brushing a slurry (essentially a mixture of Portland cement and water) into the cracks.
Mixing stucco is not difficult, but it can be messy, so wear old clothes (including heavy-duty work gloves to protect your hands) and spread a dropcloth on the work area. Pour two quarts of water into the bucket then add equal parts of cement and sand. Mix everything together, gradually adding more stucco and sand until the mixture has the consistency of a heavy paste. The stucco will harden quickly; avoid mixing more than you can apply in an hour.
Use the garden trowel to scoop the stucco from the bucket and deposit it on the cement trowel. Trowel it onto the wall in a 1/4-inch thick layer, then use the rubber float to smooth the entire spread. Work in small areas - about five feet by five feet. This will allow you time to spread and smooth the stucco before it hardens.
You can experiment with textural effects with improvised tools. You can, for example, grain the surface by dragging a piece of corrugated cardboard through the wet stucco. You can also create a pebbled surface by flicking the stucco mix from a stiff, long-bristled brush. If the texture is too rough, smooth the peaks and bumps by drawing the trowel across the surface. These techniques are not hard to master, but it's best to practice them on a piece of scrap board.
Ideally, stucco should not be painted. The color should be added to the mix so that it becomes an integral part of the medium. Then, it will not peel or wear off. Over the years, however, some stucco walls can become shabby, particularly those with numerous patches. In this case it's necessary to either resurface the wall with a new layer of stucco or paint the surface. Of the two choices, painting may be easier, but it may lead to problems in the future. If the paint starts to peel, you'll have to scrape the loose paint off the wall (this may be difficult on a textured surface) before you can repaint.
If you decide to repaint, choose a top-quality acrylic latex paint. Carefully clean the stucco surface to remove all dirt, grease and loose stucco. You can use a pressure washer for this task, but be very careful - if the pressure is too strong it could cause the stucco to disintegrate. Then apply the paint with a long-nap roller or masonry brush.