carried in a light solvent such as mineral spirits, making it
compatible with composite wood products that might be
negatively affected by the swelling associated with water-
based pressure treatments. The IPBC/PER formulation is
intended only for use in above-ground applications. The
formulation is listed as a preservative in AWPA standards,
but at the time this chapter was finalized it had not yet been
standardized for treatment of any commodities.
Alkyl Ammonium Compounds
Alkyl ammonium compounds such as didecyldimethylam-
monium chloride (DDAC) or didecyldimethylammonium
carbonate (DDAC)/bicarbonate (DDABC) have some ef-
ficacy against both wood decay fungi and insects. They are
soluble in both organic solvents and water and are stable in
wood as a result of chemical fixation reactions. DDAC and
DDABC are currently being used as a component of alka-
line copper quat (ACQ) (see section on Waterborne Preser-
vatives) for above-ground and ground-contact applications
and as a component of formulations used for sapstain and
mold control.
4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One (DCOI)
4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (DCOI) is a
biocide that is primarily effective against wood decay fungi.
It is soluble in organic solvents but not in water, and it is
stable and leach resistant in wood. The solvent used in the
formulation of the preservative is specified in AWPA P9
Type C. DCOI can be formulated to be carried in a water-
borne system, and it is currently used as a component in
the waterborne preservative EL2. It has also recently been
proposed for use as co-biocide in a copper ethanolamine
formulation referred to as ACD.
Chlorpyrifos
Chlorpyrifos (CPF) is an organophosphate insecticide that
has been widely used for agricultural purposes. It has been
standardized by the AWPA as a preservative but is not cur-
rently used as a component of commercial pressure treat-
ments. Chloropyrifos is not effective in preventing fungal
attack and should be combined with an appropriate fungi-
cidal preservative for most applications.
Treatments for Wood Composites
Many structural composite wood products, such as glued-
laminated beams, plywood, and parallel strand and lami-
nated veneer lumber, can be pressure-treated with wood pre-
servatives in a manner similar to lumber. However, flake- or
fiber-based composites are often protected by adding preser-
vative during manufacture. A commonly used preservative
for these types of composites is zinc borate. Zinc borate is
a white, odorless powder with low water solubility that is
added directly to the furnish or wax during panel manufac-
ture. Zinc borate has greater leach resistance than the more
soluble forms of borate used for pressure treatment and
thus can be used to treat composite siding products that are
exposed outdoors but partially protected from the weather.
Zinc borate is currently listed in AWPA Commodity Stan-
dard J for nonpressure treatment of laminated strand lumber,
oriented strandboard, and engineered wood siding. The stan-
dard requires that these products have an exterior coating or
laminate when used as siding. Another preservative that has
been used to protect composites is ammoniacal copper ac-
etate, which is applied by spraying the preservative onto the
OSB flakes before drying.Water-Repellent and Nonpressure
Treatments
Effective water-repellent preservatives will retard the in-
gress of water when wood is exposed above ground. These
preservatives help reduce dimensional changes in the wood
as a result of moisture changes when the wood is exposed to
rainwater or dampness for short periods. As with any wood
preservative, the effectiveness in protecting wood against
decay and insects depends upon the retention and penetra-
tion obtained in application. These preservatives are most
often applied using nonpressure treatments such as vacuum
impregnation, brushing, soaking, or dipping. Preservative
systems containing water-repellent components are sold un-
der various trade names, principally for the dip or equivalent
treatment of window sash and other millwork. The National
Wood Window and Door Association (NWWDA) standard,
WDMA I.S. 4–07A, Water Repellent Preservative Treatment
for Millwork, lists preservative formulations that have met
certain requirements, including EPA registration and effi-
cacy against decay fungi.
The AWPA Commodity Specification I for nonpressure
treatment of millwork and other wood products provides re-
quirements for these nonpressure preservatives but does not
currently list any formulations. The preservative must also
meet the Guidelines for Evaluating New Wood Preservatives
for Consideration by the AWPA for nonpressure treatment.
Water-repellent preservatives containing oxine copper are
used in nonpressure treatment of wood containers, pallets,
and other products for use in contact with foods. When
combined with volatile solvents, oxine copper is used to
pressure-treat lumber intended for use in decking of trucks
and cars or related uses involving harvesting, storage, and
transportation of foods (AWPA P8).
Nonpressure preservatives sold to consumers for household
and farm use typically contain copper naphthentate, zinc
naphthenate, or oxine copper. Their formulations may also
incorporate water repellents.Selecting Preservatives
The type of preservative applied is often dependent on the
requirements of the specific application. For example, direct
contact with soil or water is considered a severe deteriora-
tion hazard, and preservatives used in these applications
must have a high degree of leach resistance and efficacy
against a broad spectrum of organisms. These sameGeneral Technical Report FPL–GTR– 190