Why Do We Treat Lumber?
1. Biological Decay – marine borers, fungi, insects, bacteria
a. By impregnating fibers with a preservative, wood is eliminated as a food, therefore we can prevent biological decay.
2. Physical and Chemical Decay – fire, wear, chemicals
b. These are natural occurrences that can not be prevented.
1. Southern Yellow Pine
2. Ponderosa Pine
3. Red Pine These three species allow a penetration depth, which is important to provide a barrier thick enough so that any checking or splitting will not expose any untreated wood to decay or insect attack.
4. Others: Most other species do not readily accept chemical preservatives. This does not mean you can not treat other species. The AWPA requires incising to aid both chemical penetration and uniform retention.
1. Chromate – affixes the C and A chemically to the wood. The chromate reacts to make it safe for people, pets, and plants to come into contact with the wood.
2. Copper – prevents decay from various fungi.
3. Arsenate – stops decay plus it eliminates damage from insect and termite attacks.
1. Initial Vacuum – air is taken out of the lumber. This affects the amount of CCA left in the wood at the end. The amount of time in the initial vacuum is determined by the species and its dimensions.
2. Flooding the vessel – completely flooding with preservative while maintaining the vacuum.
3. Pressure period – once full the pressurization begins. The preservative solution is pumped into the tube while the pressure is raised to approximately 150 psi. The pressure is held long enough to reach penetration and uptake.
4. Initial drain – The pressure is released and the preservatives are drained back into their tanks for reuse.
5. Final vacuum – There is some preservative left between the units after the initial drain, therefore in order to dry the surfaces and not waste the preservative a final vacuum is applied.
6. Conditioning building – The lumber is placed in a conditioning bailing. This serves as a controlled environment, protecting the pressure treated material from the weather. While in the bailing the highly resistant bonds are founded to make it safe for people, plants, etc.
Handling Pressure Treated Lumber
Use the same care that is recommended when working with any wood.
1. Always wear safety glasses, dust mask and gloves.
2. Only one precaution, do not burn pressure treated wood. Dispose of scraps and sawdust with
landfill trash. Burning of treated wood releases the CCA bond with the cells.