WOOD - Materials for Civil and Construction Engineers - page 421

used for commercial applications and permanent foundations. Although CCA
was removed from the market, the EPA is not calling for the removal of it
from existing structures.
The most common replacement preservatives are ammoniacal copper
quat, or ACQ, followed by copper azole, and borate. Borate may be used in
home foundation sill plates and other “dry” applications, but borate-treated
wood is not appropriate for outdoor uses (Forintek, 2002).

■ 10.12.3 Application Techniques

Preservatives are applied by superficial treatment or by fluid penetration
processes. Superficial treatment techniques include coatings applied by
painting, spraying, or immersion. Liquid penetration into a porous solid is by
capillary action and is a function of surface tension, angle of contact, time,
temperature, and pressure.
Pressure-treated wood has greater resistance to degradation than surface-
treated wood. The preservative is forced into the entire structure of the wood.
By thoroughly treating the entire cross section of the wood, decay can be elim-
inated for an extended period of time. Some vendors of pressure-treated wood
provide a lifetime warranty for their products when in direct contact with the
ground. The key to ensuring long life is the amount of preservative retained in
the wood. Table 10.5 gives the minimum retention requirements for different
treatments and applications of Southern Pine lumber, timber, and plywood.

kg/m 3

T ABLE 10.5 Minimum Retention Requirements in for Different Treatments
and Applications of Southern Pine Lumber, Timber, and Plywood (Southern Pine
Council 1990)

Soil and Permanent

Above fresh wood Saltwater

ground water use foundation use

Ammoniacal copper
arsenate 4 6 10 41

Waterborne Ammoniacal

preservatives copper zinc arsenate 4 7 10 41

Chromated copper
arsenate 4 7 10 41

Creosote and Creosote 131 163 NR * 408

oil-borne Creosote-petroleum 131 163 NR * NR *

preservatives Creosote solutions 131 163 NR * 408

Pentachlorophenol 7 8 NR * NR *

* NR: Not recommended.

For a complete list of wood products see the American Wood Preservative Association
(AWPA) standards.

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