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 with low retention of preservative. The Reuping and Lowry are two empty cell processes commonly
employed.
5.3.3.2 Hot and Cold Bath or Open Tank Treatment. The process is most com-
monly used for treatment of poles and fence posts. Wood is first immersed in a hot bath of preserv-
ative, then moved to a cold or cooling bath.
5.3.3.3 Diffusion. Deep penetration of unseasoned wood with water soluble pre-
servatives is achieved when wood is soaked for days or weeks in tanks of preservative chemicals.
5.3.4 Preservative Chemicals. Wood preservatives must be effective against wood-
destroying organisms, yet safe from an environmental and health standpoint for the end use in-
tended.
Commonly used preservatives can be divided into two groups. The first group is the organic pre-
servatives such as creosote, oil borne pentachlorophenol, copper naphthenate and others. The
second group includes the water borne salts.
5.3.4.1 Organic Preservatives. This group contains creosote and coal tars, pen-
tachlorophenol, bis (tri-N-butyltin) oxide, and copper naphthenate.
Coal Tar Creosote and Related Products. The words coal tar
creosote and creosote are used interchangeably. This preservative is commonly used on piles,
poles, heavy timbers and railroad ties. It imparts a dark brown to black color. Creosote is effective
against most biological organisms that attack wood. It is permanent due to low volatility and it is in-
soluble in water. However, freshly creosoted wood may ignite easily. Also, the odor and oily dark
surfaces of the treated wood may be objectionable. Creosoted material cannot be painted. In
November of 1986, it became a restricted use pesticide and is available only to certified applicators.
Pentachlorophenol. Pentachlorophenol has been widely used in both
an oil and water-soluble form for pressure and non-pressure preservative treatment of wood. As of
November 1986, however, it is a restricted-use pesticide and thus available only to certified ap-
plicators.
Solutions of 5 percent pentachlorophenol in light petroleum solvents such as kerosene, mineral
spirits and similar oils are used for treating exterior millwork since they will leave a clean, paintable
surface.
Pentachlorophenol is effective against many terrestrial wood destroying organisms such as molds,
stain, decay fungi, and insects. However, it is not effective against marine borers and should never
be used by itself for protection of wood in salt water. It should not be applied indoors or where
human contact is likely.
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