Last month, in part two, we took an in-depth look at the third class of wood preservatives: water-soluble salts. We examined the problems encountered whereby arsenic is the active ingredient in preservatives, such as chromated copper arsenic and the corrosion problems associated with the new breed of copper-based, water-soluble salt preservatives, such as ammonial copper quaternary, which use ammonia compounds as their active ingredient. This month, we'll discuss the fourth and last class of wood preservative treatments: water-soluble boron compounds.

Sodium borate-also known as SBX-preservative treatment uses boron compounds, such as borax or boric acid, as the active ingredient or "carrier." Toxic to termites, carpenter ants, mold and decay organisms, boron compounds have been used as a less toxic alternative insecticide for decades. Boron treatment provides more than a surface coating while remaining no more toxic to humans than borax (but don't ingest it). Spread in concealed spaces where cockroaches hide, boric acid gets on their many legs and they then track it back to the nest. There, it is spread to the rest of the colony acting as a very effective, low toxicity insecticide.

CCA's other Achilles' heel

As we saw last time, CCA never fully penetrated to the "heart of the wood"-boron-based treatments do without releasing any volatile organic compound. Typically, boron-based wood preservative treatments are not approved for exterior/outdoor applications, such as decks, playground equipment, picnic tables, etc., since they are water-soluble. Some manufacturers, such as EnviroSafe, use the borate compound disodium octaborate tetrahydrate as a low-toxicity preservative treatment for lumber and plywood. The DOT is "set" or embedded in the wood structure with a sodium-silicate application.

The manufacturer claims their product EnviroSafe Plus to be effective against the dreaded formosan subterranean termite, as well as other pests, such as beetles, carpenter ants, fleas, silverfish and cockroaches. As well, it is said to have anti-fungal characteristics. After treatment, the wood retains its natural color characteristics and will not off-gas any VOCs into the interior environment. Most typically, it is used for interior, unexposed applications, such as studs, sill plates, joists, rafters, moldings and trim.

Caveat emptor

With the ban on CCA at the end of 2003 and subsequent phase-out of existing inventory through 2004, many lumber suppliers across the country turned to ACQ and copper azole as the heir-apparent successor to CCA. They quickly learned of the corrosive nature of these preservatives and sought out alternatives. Boron-based treatments seemed to be the logical solution to this vexing problem but only for a while.

Manufacturers who claimed that their sodium-silicate applied boron-based preservative treatments could be used for exterior, exposed applications had to eat some humble pie. DOT treated wood, when hit with a hammer, disperses a white powder.

Along with ACQ, sodium-silicate borate proved to be twice as corrosive as CCA and as mentioned in part two, steel fastener and connector companies, such as Simpson Strong-Tie, issued warnings concerning ACQ and EnviroSafe Plus as being highly corrosive to metal connectors and fasteners. EnviroSafe Plus backs-up its product with a 40-year transferable warranty and like all boron-based wood preservative treatments, they are suitable only for unexposed, interior applications, such as those aforementioned.

There are many manufacturers of water-soluble boron compound wood preservative treatments:

• Tim-Bor: Originally manufactured by U.S. Borax Inc., Tim-Bor is now made by Nisus Corp. It is a DOT boron-based wood treatment that is applied by spraying, dipping or soaking. It is sold in powder form and is mixed with water for application.

• NiBor-D: Also manufactured by Nisus Corp., it is very similar to Tim-Bor (DOT boron-based treatment) in that it comes in powder form and is mixed with water. The presence of moisture allows penetration into the wood and does not off-gas any VOCs that would be intolerable to sensitive people. It is most effective on damp (not dry) wood.

• Bora-Care: Another product from Nisus Corp., this treatment also contains DOT but in a glycol solution. This allows for penetration into dry wood-particularly where there is an active infestation. It will totally penetrate the wood and has a mild odor when wet that may offend some sensitive people. Jecta is a concentrated version of Bora-Care that is useful whereby the wood surface has a water-resistant coating. A 30cc syringe is used to ingest the preservative into small, pre-drilled holes in the wood.

• Termite-Prufe: Again, like Tim-Bor and NiBor-D, Termite-Prufe is a DOT powder mixed with water. It is sold in one-pound cans in hardware stores and manufactured by Copper-Brite Inc. It also, as with all boron-based treatments, will remain water-soluble and should be used only in unexposed locations. It is typically applied when the framing lumber is made weather-tight by the siding and roof.

• SmartGuard: Until SmartGuard, made by Louisiana-Pacific, borate PT lumber was not readily available in the U.S. SmartGuard uses a zinc-borate compound with similar characteristics to the DOT powder used in Tim-Bor for all framing lumber, sheathing and siding. Where there is a problem with the dreaded FST, such as gulf and southeastern states, SmartGuard is widely available.

• Advance Guard: Made by Osmose Inc., Advance Guard uses the same DOT powder as Tim-Bor. In fact, the company supplies Louisiana-Pacific for the SmartGuard preservative treatment.

• Ultra Rods: Once known as "Impel Rods," Ultra Rods are borate-impregnated rods available in a variety of sizes. Often used on historic projects where damp-wood is present (plus 20 percent moisture content), holes are drilled into the wood and the rods inserted. Once in place, the boron compound in the rods migrates into the damp wood protecting it from rot and infestation.

A lifetime away

Distributed by Schroeder Log Home Supply Inc., LifeTime Wood Treatment is often used on log homes. The manufacturer Valhalla Wood Preservatives Ltd. claims the secret formula is non-toxic to plants, people, animals and soil-based microorganisms. It imparts a silver patina when applied to above ground exposed wood surfaces, such as fences-but there is ambiguous data concerning in-ground applications. As such, it acts more as a wood treatment than a preservative. Like DOT, it is a powder mixed with water and works well in dry climates. It has been successfully used in a wide variety of applications in the U.S., Europe and Canadian national parks.

A distributor for several boron-based products is WoodcareSystems Inc. Though boron-based preservative treatments remain water-soluble, it is continued exposure to rain rather than one-time exposure that will cause the boron compounds to leach out. Likewise, wood siding treated with boron PT should not be left exposed since it will leach upon continuous exposure to rainwater. If properly painted, such leaching will not occur.

Some manufacturers of boron-based PT are not yet listed with the International Code Council. Like many other green building products, it is taking advantage of the little known stipulation in almost all building codes that allows building product/system manufacturers to seek independent approval of their product/system by local building code officials.

Next time, in part four, we'll take a tangential look at this caveat, the role of building codes in general and how it plays into the next generation of wood preservative treatments.