Stucco is an ancient, even prehistoric, building material. Many of the most famous ancient civilizations used it: the Greeks, Romans, and Aztecs. The Egyptian pyramids were once stuccoed too! It used to be limited in color to the earthly elements it’s made from (lime or Portland cement, sand, and water), but you can now see it in a variety of shades. Colored stucco is achieved by adding pigment to the final coat as it’s applied, creating a layer of color about 1/8-inch thick. But what about when it comes time to update the color of your exterior or match the old color where repairs were made?
When You’re Applying Fresh Stucco
Unless you’re making a fresco (like The Last Supper), do not paint fresh stucco. In fact, the floor under The Last Supper is covered with flakes of paint and the famous mural has to be regularly restored and repaired.
Stucco is porous and it needs to breathe. Moisture penetrates the surface and then evaporates away. When it’s installed, a waterproof membrane (tar paper, house wrap, Styrofoam, etc.) goes between the stucco and the structure of the house, so the inside stays dry.
The final pigmented coat of stucco goes on as part of the installation process, so when the stucco is done, it’s done. If you were to paint, you’d have to wait for the stucco to dry and cure, which can take weeks. Not only that, but the paint interferes with the breathability of the surface. Moisture can become trapped in the wall between the membrane and the paint. At best, this causes the paint to bubble, peel, and chip as the moisture forces a way to escape.
Worse than that, water can gather at the base of the wall, fostering mold and bacteria and creating rot that will eat through the membrane and into the structural wood.
Properly applied, the color coat of your new stucco can last for decades. Paints will not have comparable durability and you’ll still have to paint again in a few years even if you don’t have any problems, so it’s better to go with the color coat ultimately.
When You’ve Got Old Stucco
What to do with old stucco depends on several factors. What’s the condition of the stucco? What color do you want? What do you want to spend? Is it already painted?
If your stucco is in good shape, your best option is to clean it with a pressure washer (not too harshly) and then cover it with a “fog coat.” This is a very thin coat of Portland cement, water, and pigment (no sand) that covers the surface like paint, adding a layer of color that bonds to the structure of the existing stucco. If the stucco is cracked, chipped, or spalled, it needs to be repaired and then recovered with a whole new color coat.
You can only add so much pigment to stucco, so regardless of whether you’re doing a color coat or a fog coat, it isn’t possible to achieve very dark colors. If you really must have an aubergine house then you need to use an elastomeric coating that preserves the breathability of the surface and is flexible and strong enough to bridge small gaps and cracks in the stucco.
Restuccoing a house is not cheap. In the long run, it can save you money because you will probably never have to do it again, but unless you’re a skilled DIYer this isn’t a do-it-yourself project. A fog coat will cost you less and goes on much easier. Elastomeric coatings run about the same as the fog coat, but you have to be sure to use the right stuff. The cheapest option is always painting, but that comes with the knowledge that you may have to do it again in a few years.
If there’s already paint on your stucco, you cannot stucco over it. The new material will not bond to the paint and will crack and fall away in short order. That includes stuccoing a whole wall, or just patches or repairs here and there. If your stucco has fared well under the paint then you can paint over it. However, if you have any repairs to do then you’ve ended up in the most expensive situation.
You need to sand blast the paint and bad stucco off the house, re-stucco, and apply a color coat. This is why the stucco shouldn’t have been painted in the first place and why it is generally not recommended.