Chaco is famous for its masonry, and rightly so. While there are many things that set Chaco apart from other cultural systems in the prehistoric southwest, probably the most obvious to modern visitors is the fineness and elaboration of the stonework used to construct the major great houses in the canyon such as Pueblo Bonito and Chetro Ketl. Masonry style has also been one of the main techniques for dating and interpreting architectural stages ever since Neil Judd’s excavations at Pueblo Bonito in the 1920s. In the minds of many, the fine stonework of the Bonito Phase is the essence of the Chaco style.
Given this attitude, it’s hardly surprising that people are quite often shocked to hear that the Chacoans, like other ancient Puebloans, actually plastered over all of their stonework with a mud plaster, so the fine masonry that we find so aesthetically appealing would not actually have been visible at the time. (As Steve Lekson notes in his study of great-house architecture, not all the walls were actually plastered, but the ones that weren’t were interior rooms, probably for storage. All exterior walls, and the interior walls of living and ceremonial rooms, were plastered.) One of the questions we get very frequently, then, is why they would have done this.
It’s not at all clear why the Chacoans would have put so much effort into masonry only to cover it, but they certainly did. Some interior rooms were whitewashed and painted, which may provide one possible answer. It’s possible that exterior walls may have been painted as well, but the plaster typically doesn’t survive well enough on exterior walls to tell. It’s also possible that a smooth surface on the exterior was considered aesthetically preferable, although again it’s very hard to tell what the exterior walls would have actually looked like.
One rather more practical explanation for the plastering could be that it facilitated maintenance. Modern pueblos are generally plastered all over, whether they are made of stone or adobe, and replastering is generally an annual event in which the whole community participates. The plaster protects the walls from the adverse effects of rain and snow, which, while not extremely common in the southwest, are certainly common enough to make walls made out of adobe or stone with mud mortar deteriorate rapidly if not maintained (as the state of most ancient ruins certainly attests).
Another question we get somewhat less frequently, but which I’ve heard a few times recently, is why we today don’t plaster the walls. It would certainly make preservation work a lot easier to just cover all the walls with mud rather than doing the laborious and tedious repointing of mortar joints that our preservation crew does on a constant basis, and it would actually in some ways be more “authentic” to show how the walls likely looked at the time, even if the actual plaster were modern.
And, indeed, there is one room, the famous “covered room” in Pueblo Bonito with an intact ceiling, where the original plaster was recently covered over with replacement plaster because it was getting so damaged by the high volume of visitation the room gets. This room is the only one in Pueblo Bonito that is accessible to visitors where it is possible to get a reasonable sense of what all the rooms were originally like.
In most places, however, we don’t replaster, despite the potential benefits of replastering for preservation. This seems to be a rare case of interpretive concerns outweighing preservation concerns rather than the other way around. Basically, the very fact that people associate Chaco with its masonry makes it very difficult to justify covering up that masonry, even if it would be both better for preservation and truer to the original state of the buildings. At this point the image of Chaco is at least as important to the visiting public as the truth behind that image, and the stonework is such an integral part of that image that the public outcry if it were covered up would likely be intense.
So we, unlike the Chacoans, leave the stonework exposed to the elements, and work much harder than these notoriously hard-working people ever did to keep it in place. I wonder what they would think if they saw this. I suspect they would laugh.