CHAPTER 5. PRESERVATION OF NEW WOOD PRODUCTS TO PREVENT
DECAY AND INSECT ATTACK
5.1 NEED FOR PRESERVATIVES. In the past "naturally durable" woods, such as green heart,
cypress, redwood and cedar were used where decay fungi, insects or marine borers were a threat.
As discussed in Chapter 2, the availability of these woods is now limited and they are generally
more costly than treated wood products. Consequently, most wood is now treated with preserv-
atives to protect it from degradation by decay fungi, insects and marine borers. Preservatives are ap-
plied to wood by nonpressure processes that provide superficial protection and by pressure
processes that force chemicals into wood.
5.2 SUPERFICIAL TREATMENTS. Preservatives applied by brushing, spraying, dipping or
vacuuming processes do not penetrate deeply into the wood. These treatments are not intended to
protect the wood from sustained exposure to degrading organisms.
No commercial standards govern the use of preservatives applied by brushing or spraying. Dip
treatments of exterior millwork, such as doors and windows, with water-repellent preservatives
(WRP) and non pressure treatments for wood packaging for the DOD are described in either com-
mercial or U.S. government standards.
Water-repellent preservatives contain a wax, resin and other components to cause wood to shed
(repel) water, and a preservative to prevent decay.
5.2.1 Treatment Quality. To meet standards set by the National Wood Window and
Door Association, water-repellent preservative treatments for millwork must reduce the normal
shrinking and swelling of wood by at least 60 percent and must leave the surface of the wood clean,
dry and paintable. Preservatives included in water-repellent formulations must be effective in
5.2.2 Non Pressure Methods Of Application.
18.104.22.168 Brush. Brush treatments should be flooded onto the surface and not
brushed out thin, like paint. Checks and other openings should be saturated to the point of refusal.
The wood should be well dried before treatment or it will not accept preservatives applied in this
22.214.171.124 Spray. A coarse spray should be used to minimize health hazards. Special
precautions should be taken to avoid drift.
126.96.36.199 Dip. Dip treatment involves immersion of wood materials in a tank of pre-
servative until the wood absorbs the appropriate amount of solution. The NWWDA requires a soak-
ing period of 15 seconds when individual parts or units are treated and 3 minutes for batches or