Wood pressure preservation
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Creosoting
Creosoted timber has a low electrical conductivity, which is recognized in the use of creosote-impregnated poles for electrical power transmission and for sleepers (railroad ties).
Vacuum pressure impregnated wood is wood that, through the application of a preservative, is protected for many years against fungi and insects. To achieve this effect, wood is put in a closed horizontal cylinder - the autoclave - and then the air is drawn out of the cylinder and out of the wood cells. Then the preservative is admitted and the content of the treatment cylinder is put under pressure. By doing this, the preservative enters deep into the wood cells. After this, the vacuum is sucked again to make sure that any excess preservative is completely removed. The process is brought to an end by a fixation treatment to ensure that the applied preservative will remain in the wood by entering into a chemical reaction with the wood. To achieve this effect, wood is put in a closed horizontal cylinder Ð the autoclave Ð and then the air is drawn out of the cylinder and out of the wood cells. Then the preservative is admitted and the content of the treatment cylinder is put under pressure. By doing this, the preservative enters deep into the wood cells. After this, the vacuum is sucked again to make sure that any excess preservative is completely removed. The process is brought to an end by a fixation treatment to ensure that the applied preservative will remain in the wood by entering into a chemical reaction with the wood.
CCA treatment
CCA is composed of the oxides of chromium, copper, and arsenic.
The copper in the wood serves as the fungicide whereas the arsenic protects the wood against insects.
The chromium fixes the copper and arsenic to the wood.
CCA can be separated into Type "A", "B", or "C" depending upon the relative proportions of metals. The relative proportions range from 35-65%, 16-45%, 18-20% for chromium, arsenic, and copper, respectively.
| CCA-Type A | CCA-Type B | CCA-Type C | |
| Chromium as CrO3 | 65.5% | 35.3% | 47.5% |
| Copper as CuO | 18.1% | 19.6% | 18.5% |
| Arsenic as As2O5 | 16.4% | 45.1% | 34.0% |
The amount of CCA utilized to treat the wood or retention level depends upon the particular application for the wood product:
| Application | Retention Value (lb/ft3) |
| Above ground: lumber, timbers, and plywood | 0.25 |
| Ground/Freshwater contact: lumber, timbers, plywood | 0.40 |
| Salt water splash, wood foundations: lumber, timbers, and plywood Structural poles |
0.60 |
| Foundation/Freshwater: pilings and columns | 0.80 |
| Salt water immersion: pilings and columns | 2.50 |
