In part three, we took an in-depth look at the fourth class of wood preservative treatments: water soluble boron compounds. We saw how, despite some manufacturers' claims, sodium silicate applied disodium octaborate tetrahydrate, a low-toxicity preservative treatment for lumber and plywood, proved to be unsuitable for use in exterior/exposed applications. Water-soluble sodium silicate will leach out of wood and, when it interacts with air, an unsightly white crystalline dust forms on the surface of the treated wood-particularly aggravated by hammer blows.
Additionally, like the new breed of copper-based wood preservative treatments, it proved to be highly corrosive to metals. This month, in part five, we'll conclude this series all about wood preservative treatments with a technology and product that many hope will be the "silver bullet" the construction industry has been searching for since chromated copper arsenic was banned at the end of 2003.