On Insects, Rot and the 20 Mule Team
Ed Crocker

Is it spring? It's hard to tell given the topsy-turvy weather patterns we've been experiencing, and I usually wait until I see barley sprouts in our freshly mudded walls before I declare the arrival of the season. Nevertheless, the season formerly known as winter (to cop a phrase from my favorite weatherman) is ebbing away, and we have passed the vernal equinox; it is time to begin thinking about gardens and Easter and closet cleaning -- if those are our interests. My interest (some call it an obsession) with earthen buildings, leads me to look at changes of season as opportunities to investigate the behavior of materials and to solve specific, weather-related problems pertinent to adobe. And if it's spring, it's time for some rain -- and for wood-boring insects to set about their insidious activities.

It is characteristic of earthen structures that they embed wood, such as lintels, vigas and rafters, in soil. This may seem like a sure-fire formula for deterioration, but the old-timers (as usual) knew something that we have forgotten; that wood, like adobe, can get wet with near impunity as long as it can dry out rapidly when the periodic source of moisture relents. Back when earthen buildings were plastered with permeable materials, the structures worked as systems -- the components were made using compatible substances and so expanded and contracted at the same rate and got wet and dry in corresponding cycles. With the advent of Portland and elastomeric plasters, all that has changed and moisture that enters a hard-plastered wall is trapped within. That leads to accumulations of water that destroy earth and wood both.

The wooden elements most susceptible to damage, from both moisture and insects, are those that are partially revealed to the atmosphere (such as window sills, beams and protruding viga tails) and those that are embedded in earth but exposed to water from a leaky roof, bad plumbing or accumulations over years from wet-mopping and vegetable steaming. Insects are amazing opportunists, and will invade via the most unlikely routes. I've seen termite columns (the little tunnels they build to get from place to place in the otherwise open air) that climb block footings to joists or that zero in on a dime-sized parcel of exposed wood. In short order the wood is riddled and has lost its structural qualities. Needless to say, the best solution to insect and moisture problems is the never-overrated "ounce of prevention."

And there is a benign (to people) material that will help you exercise just that. Remember the old soap ads that featured "20 Mule Team Borax"? Though Boraxo seems to have given way to other cleansing products, the basic compound, boron, has found a new and even more useful niche in checking the advance of both rot and insects in wood.

Borate compounds are nutrients for plants, including rot fungi, and are necessary for cell division. But boron in large doses burns the fungi in much the same way as over-fertilizing will kill a lawn.

Wood-boring insects have almost no tolerance for borate. In small doses it kills the microbes that process wood glucose in their systems and they starve to death. Should they bore into a piece of wood that is saturated with a borate compound, a catastrophic chemical imbalance results and quickly kills the offender.

We have been using borates in building conservation projects from northern Minnesota to southern New Mexico for years -- with amazing results. We prefer the material in solid form that is implanted in drilled holes at regular intervals. It works best in green wood with greater than 16% moisture because that moisture helps the dispersal of the boron. We have been very successful, however, in treating old, dry wood that occasionally gets wet. Once the moisture reaches the boron tablet, it dissolves and travels wherever the water takes it.

If you would like more information on borate treatments for wood, give us a call or send an e-mail.