Termites in Mud? Back to Bam
A few months ago in this space I reported on the earthquake in Bam, Iran and commented that when the dust settled the popular view that adobe is a poor and dangerous building material would likely be debunked. Not all of the data, research and ideas are in, but here is an update on the likely causes of damage.
In mid-April the Iranian Cultural Heritage Organization, UNESCO and the International Council on Monuments and Sites organized a meeting of experts in Bam to assess the damage and make recommendations to guide rebuilding. A few of my colleagues have been generous in providing an advance look at the findings. During the short duration of the site visit (four days) a great deal of time was spent in meetings and panel discussions with, I am told, insufficient time allotted to prowling the site itself. One of the participants and long-time friend, Randolph Langenbach, adjusted his schedule to spend a couple of additional days in the rubble. During that less hurried time he made some observations that led to at least one remarkable conclusion. Much of the seismic damage in Bam was predicated on termites.
Termites? In mud? Strange but true and resulting from newer material used in restoration.
When I first reported on the Bam earthquake, which occurred on the heels of my visit to the area in December, I noted that much of the famous and deeply historic Bam citadel had been reconstructed about fifty years ago. Whenever reconstruction takes place with adobe, one of the key technical points is to interlock the new work with the old. This is typically done by selectively removing adobes in either a stepped or "toothed" configuration and fitting new ones as deeply into the existing walls as feasible. This detail is frequently overlooked and the new material becomes a veneer instead of an integral part of the structure. This happened at Bam and according to some present at the workshop, the cleavage between the old and new was clearly visible.
However, much of the reconstruction was massive and would be expected to behave like the older material. This was not the case and Randolph, in an epiphany of sorts, associated the newer materials with portions of the rubble that had been riddled by termites. The insects did not attack the mud, but the straw and organics traditionally used in the mix. They attacked it so thoroughly that virtually no vegetal material remained, and its vacancy left empty space. The earthquake caused the riddled mud to disintegrate, almost to liquefy, into dust.
Why did some of the older walls elude such damage, as indeed they did? I have speculated to Randolph and others that there is the possibility that the vernacular builders of Bam built the remedy into the mud. Borates, derivatives of the mineral Boron, are highly effective insecticides that destroy the digestive enzymes of wood-eating ants and termites. Boron is also commonly found in desert environments such as are found around Bam.
I speculate, and invite response to the idea, that the builders of Bam used experientially derived knowledge of a common local material to make the building termite resistant. As part of the plan for rebuilding Bam, I have suggested that the same ancient, inexpensive and effective solution be used by soaking the straw in water containing borates, and that the same water be used to mix the mud.