Boro-conservation For Endangered Historic Structures
January 1997

Take a giant red cedar, carve it with icons and images of your folklore, history, or ancestors, sink it into the forest floor, wash it with 95 inches of rain per year - and you create a perfect environment for fungal decay.

The totems of Alaska and British Columbia, designed to commemorate indigenous Indian heroes and legends, are also designed to welcome and encourage decay fungi and a host of other wood-rotting organisms. Of all the standing totems in the Sitka National Historical Park in Alaska, for example, only one now truly dates back to the 19th century, the others are replicas. A replica totem carved in 1964, no doubt from a tree some 200 years a-growing, became so rotten that it had to be moved indoors in 1978. But that was before the concept of boro-conservation had been extensively researched, let alone adopted as a treatment by the U.S. National Park Service.

Boro-conservation may be defined as the preservation and restoration of wooden structures by means of borates. It is still a developing science in which Borax Technology works as a partner with environmental, academic, archaeological, and national heritage organizations globally.

Borax involvement really began when the Swedish warship Wasa, built then sunk in 1628, was recovered from the Baltic seabed in 1961. Her waterlogged timbers, so long protected by mud and brine, had to be dried out but at the same time protected from the onset of decay. The technique evolved was continuous spraying with a mixture of polyethylene glycol, boric acid, and borax. Incorporation of borates into the spray solution enabled them gradually to diffuse into the ship's timbers, and provide lasting protection against wood-rotting organisms. Spraying lasted from 1962 until 1979.

Similar problems were posed when the Mary Rose, flagship of King Henry VIII which sank near Portsmouth in 1542, was brought to the surface in 1982. Her wooden artifacts were also successfully treated with borate and polyethylene glycol, but the hull itself was initially sprayed with recycled, refrigerated water. When biological deterioration was discovered, PolyborŪ disodium octaborate tetrahydrate was added to the spray along with a quaternary ammonium compound. Again the waterlogged condition of the timbers provided diffusion pathways for the borate.

Wooden vessels which remain afloat present a different set of challenges. Parts of the ship's hull and exterior can partially be protected by seawater, but the decks and interior timbers are highly vulnerable to scourges such as Basidiomycete decay, problems which are exacerbated over the years by the penetration of rainwater. The schooner Wapama, which plied the west coast of America for some 80 years, became riddled with rot. Her remedial treatment with Tim-borŪ wood preservative won a National Historic Preservation award in 1988.

In Dundee, Scotland the almost indestructible ship built for Scott of the Antarctic in 1901, is now being treated for very extensive wet rot by a new development in boro-conservation technology. The oak and greenheart timbers of the Royal Research Ship Discovery were first raised by steam treatment to the temperature at which all decay fungi are killed - 70°C/158°F. Then they were treated with Tim-bor to prevent any rot returning. This technique was pioneered for Britain's Maritime Trust and Dundee Heritage by the timber research department of Imperial College, London in association with Borax Technology. The Discovery program also involves removal of irredeemably damaged wood and replacement by new timber which has been Tim-bor treated.

From sea to land, though not exactly dry land; the slipway from which I.K. Brunel's pioneering Great Eastern was launched in 1850 has recently been discovered in London's dockland, after being buried in mud for 130 years. The timber, probably Baltic redwood, had survived well, still yielding the sweet resinous odor and 50 percent moisture content of freshly felled pine. Removal of the mud, however, was bound to create a decay hazard for the heartwood. In this case, the slipway itself and its piles required different forms of protection. The piles were treated with borates, including a solution of 40 percent disodium octaborate tetrahydrate.

Historic houses

While parts of Europe retain many pre-18th century buildings whose wood has proved relatively immune to biodeterioration, America's 19th century timber-framed houses appear more at risk. Decay fungi and wood-boring beetles play their part, but the main culprit is the termite. Termites are keen to share in the American way of life, from log cabins to millionaires' mansions.

With Tim-bor Insecticide, Borax believes it has developed one of the most effective termiticides. Ron Sheetz of the National Park Service's conservation division says: "Borate preservatives appear to be the safest and most effective protection treatment available today, when applied properly.

"Borates are odorless, do not vaporize, and do not discolor wood. Structural properties of the wood are not affected, and metal fasteners, such as nails, screws, and braces, with the exception of aluminum, are not corroded. When high enough concentrations are used, the treated wood is also fire resistant. Paints and water-repellents can be applied over borate-treated wood. Borates can be applied by brush, with a garden sprayer, by injection, or by dipping." [National Park Service 'Conserve O Gram' No. 7/3]

Historic American buildings recently or currently being Tim-bor protected from termites, beetles, and rot include the 1842 Russian Bishop's House in Sitka, Alaska; Pinkerton Rouse Place, an 1843 mansion in Lexington, Kentucky; the 1850s Pontalba Building in New Orleans; the 1890s Belleview Mido Hotel, Belleair, Florida; and Jefferson County Museum in Texas, to say nothing of Hollywood's very own YMCA dating from 1921.

But what of those totem poles in their rainy corner of the American Northwest? Borates are water soluble, and can leach out of wood, particularly when in ground contact. Treatment of pole bases and support posts is therefore more of a problem than treatment of the carved portions of the pole.

There are two or three options. Currently the National Park Service treats the carved poles with Tim-bor or other sodium borate solutions so that borate diffuses throughout the cross-section. Then it brushes a water and mildew repellent over the treated wood. For the lower sections and support posts, it uses a paste of borax and copper naphthenate held in place by a polyethylene 'bandage'. For the mortise and tenon joinery employed in replacing items such as raven beaks, the fused borate rods originally developed to protect railway ties (sleepers) and telephone poles are being used increasingly. The fused rods release their borate as and when it is required, in response to moisture, over a ten year period, and can be replaced by fresh rods as required.

Across the world there are innumerable wooden structures of cultural, religious, or historical significance that are continuously at risk from wood-destroying organisms. In most cases, the developing science of boro-conservation could effectively protect them.

Acknowledgements to Ron Sheetz, formerly Furniture Conservator, National Park Service, Harpers Ferry, West Virginia; and Dr. David Dickinson, Senior University Lecturer, Imperial College of Science, Technology and Medicine, London.