Treated Lumber
Treated lumber is used
to preserve the wood and should be used where the wood touches the
concrete as in the picture above.
Chromated copper arsenate (CCA) is a wood preservative
used for timber treatment, in use since the mid-1930's. It is a mix of
copper, chromium, and arsenic formulated as oxides or salts. It
preserves the wood from decay fungi, wood attacking insects, including
termites, and marine borers.
It also improves the weather-resistance of
treated timber and may assist paint adherence in the long term.
Timber or lumber that is treated with a preservative
generally have it applied through vacuum and/or pressure treatment. The
preservatives used to pressure-treat timber are classified as
pesticides. Treating timber provides long-term resistance to organisms
that cause deterioration. If it is applied correctly, it extends the
productive life of timber by five to ten times. If left untreated, wood
that is exposed to moisture or soil for sustained periods of time will
become weakened by various types of fungi, bacteria or insects.
CCA is known by many trade names, including the world-wide brand
Tanalith. The chromium acts as a chemical fixing agent and has little or
no preserving properties; it helps the other chemicals to fix in the
timber, binding them through chemical complexes to the wood's cellulose
and lignin. The copper acts primarily to protect the wood against decay
fungi and bacteria, while the arsenic is the main insecticidal component
of CCA.