Textures of Earth: Stucco and Plaster in New Mexico

So one of my most often asked questions about architecture in New Mexico is "Why do the stuccos look so different?" Which if people really knew what to ask, would actually be "What is the difference between earth plasters and stucco?"

Honestly, I had no idea what the difference was until I moved to Taos and started doing historic preservation around New Mexico, because everywhere I had worked previously, we used synthetic stucco. So I had to learn, which I did by participating in the enjarre at Saint Francis Church in Ranchos Plaza and various historic preservation training events around the state.

that's me, working on the southside fence at St. Francis

The first difference, which is a difference pretty much world-wide, between stucco and plaster is that stucco is used outside and plaster inside. They have slightly different ingredients, or similar ingredients in different proportions, for durability and finish reasons. But that's an outside thing.

What makes New Mexico stuccoes and plasters so awesome is that they have more than a thousand year history. Without getting into too much technical detail, the earth plasters we use today are very similar to the ones that the ancient forebearers of the Pueblo people of New Mexico used. They are constructed of a mix, varying depending on location, of clay, sand, straw (an agriculture byproduct), and water. Yes. I'm serious. It's like making mud pies on a grand scale. And they are SUPER fun to apply. One of the old golondrinas at the church taught me one of the myriad of ways to apply earth stucco. It involved making a mud ball, like a snowball, and flinging it with all my might at the wall from about 2 feet away. It was satisfying and cathartic and, once you get the hang if it, application went very quickly.

Earth plasters are EXTREMELY sustainable, as they are:

• locally-obtained, produced, and applied
• use sweat equity
• can be done by anyone
• respond to nature like the earth would, by breathing

Now, these beautiful finishes require one thing that made them very nearly obsolete. As people had less time for maintenance, this became the death-nail for earth plaster:

 These walls require remudding annually.

But, they are gorgeous. They are amazingly cool (temperature-wise) to the touch. Sadly, there are very few examples of these finishes left in Taos. If you'd like to see them, you'll have to go to The Hulse/Warman Gallery on Paseo Norte, the Martinez Hacienda on Ranchitos Road, the Saint Francis Church in Ranchos, or El Meze on Paseo Norte.

Fresh earth plaster at St. Francis

Fine straw in this earth plaster at El Meze

Now, there is a version of white plaster that does not use straw, it only uses clay, sand, lime, and water. That's called lime plaster (oddly enough) and it's the white "paint" you see under the portals in lots of earth-plastered historic buildings throughout New Mexico. The reason these white areas are limited to under portals is actually quite logical - they reflect light better - illuminating the shaded areas more effectively that earth tone colors - and because the coating is really like an interior plaster, it can only really wear well under cover.

moth on a modern stucco wall

The last kind of plaster is really stucco. Its either cement or elastomeric (basically a rubbery kind of plastic) based. The cement kind is way cheaper, and the elastomeric version is very expensive but lasts a really long time. The downside of both these stucco systems is that they basically kill historic adobe.  As a preservationist, I am always devastated to find a historic building has been cement stuccoed. It's brought me to tears on more than one occasion. Because historic adobes weren't made with cement, they are, well... I don't know how to put this except to say it... they are alive. They drink sustenance (humidity) and they breathe - shrinking when the environment is too dry and puffing up when its wet. Once they are "encapsulated" in a non-breathing coating, they start to choke, and then they break down. Moreover, once these stuccoes form a crack, water seeps into the crack and then gets trapped in the wall, and basically turns the wall structure to mud. St. Francis and many other churches across New Mexico have almost been lost when they removed the cement plaster and found piles of sand beneath. On new frame or CMU (cinderblock) structures, these products are fine. For the REAL New Mexico, they are not.

So there you have a small taste of the difference between stuccos and plasters in New Mexico. Hope this helps!