Natural durability is a simple measure of the rate at which wood decays. Although decay is inevitable for wood in the forest, it is not inevitable for wood in use. Some woods are susceptible to fungal decay and may be completely destroyed, but have good natural resistance to wood insect pests. If wood with suitable natural durability is not available, antiseptic methods must be used. Although this method is not a panacea, it is very effective for wood that is permeable enough to reach the required depth of impregnation and can absorb the preservative.
1.The necessity of wood preservation.
Is it worthwhile to increase investment in wood preservation? This is a question that must be debated clearly. In the eyes of environmentalists, preservation is a powerful measure to reduce the demand for wood and thus preserve our forest resources. Economists have various reasons to want to preserve our forest wealth, but the principle remains the same. Countries that import wood want to preserve wood in order to reduce wood imports and save foreign exchange, while countries that export wood also want to preserve wood in order to reduce the domestic demand for wood for repairs and thus keep as much wood as possible for export. Even in the most primitive tropical jungle villages, wood preservation has great economic significance. Because in those environmental conditions, various fungi, termites and other organisms that harm wood also cause considerable damage to wood. People spend unbearable time and energy to repair wooden buildings, such as houses and bridges. Experienced preservation, including choosing more durable preservatives or adopting simple preservation methods, can double the life of buildings. In this way, more time and energy can be spent on improving the lives of villagers and perhaps planting additional crops to sell after harvest. If untreated building wood is damaged by fungi and insects, the waste caused will not only be the cost of the wood to repair it, or this cost plus the labor wages required, but also the maximum economic loss due to the failure of the building. There is also a frequent argument that such building damage can be avoided through regular inspection, but this does not reduce the loss of business caused by the closure of the business due to repair and replacement of wood.
Treated wood must be considered as an entirely new building material, and not as a mere modification of wood, for treated wood can be used in entirely different environments, and certainly in places where exposure is more severe. The obvious advantage of treated wood is that it can be used without consequence where decay is inevitable for untreated wood. It may also be argued that many competing materials enjoy the same reputation in many cases. But in fact, there are many advantages to using wood. Building with wood is extremely simple, and even with advanced production methods, the cost of machine tool installation is lower than that required for other competing materials. Wood is an ideal material for building individual structures for special purposes, whether in small or large quantities. When these processing properties of wood are considered together with other advantages such as high strength-to-weight ratio, good insulation, fire resistance and unique artistry when used as decorative panels, it is difficult to understand why people still often raise the issue of alternative materials! Among all building materials, wood also has its own unique characteristics, that is, it is a renewable resource and can be cultivated artificially, while other competing materials such as stone, brick, metal and plastic are all made from easily exhausted mineral resources.
Due to the above advantages of wood, it is not afraid to compete with competing materials, but the following prerequisites must be met, that is, effective use must be made, and durable materials must be selected or anti-corrosion treatment must be carried out to ensure that it is completely resistant to corrosion during use.
2. Anticorrosion treatment methods
Select the following methods appropriately according to the moisture content of the wood, the difficulty of injection, and the purpose (indoor or outdoor use, the required durability).
(1) Coating: Apply to dry wood more than twice, once every 2-3 years, which has a certain effect.
(2) Spraying: It works quickly but the loss of the agent is large, so pay attention to health issues. When spraying wet logs in mountain lumberyards to prevent bacteria and insects, use a sprayer to spray.
(3)Soaking: Soak in the liquid for a few minutes, suitable for small wood.
(4) Burning: Burn the surface of the wood so that the carbonized layer cannot serve as a source of nutrition for decay fungi, which can prevent fungal damage. However, cracking cannot be prevented, so it should be used together with the liquid immersion method.
(5) Drop injection method (Bucil method): A method of injecting water-soluble liquid into logs with bark after felling from a high place using a drop.
(6) Diffusion method: Adjust the water-soluble agent into a high-concentration liquid and apply it to wood with a high moisture content (surface moisture content of more than 30%), or apply it fully by immersion, stack it tightly, cover it with plastic cloth, and leave it for a certain period of time. During this time, use the osmotic pressure to inject the agent into the wood. This method is suitable for veneers, boards, square timber, and logs (try to remove the bark). The disadvantage is that it takes a certain amount of time (2-4 months for logs with sapwood thickness of 3-5 cm), and the advantage is that it does not require special equipment and machinery.
(7) Slotted warm and cold bath method: Add the agent into the barrel, heat it to soak the dry wood, and then cool it. Oily, oil-soluble, and water-soluble agents can be used.
(8) Decompression oil boiling method: (Bolton method) The wet wood is soaked in 90-100oC creosote oil, decompressed to remove the moisture inside the wood, and then pressurized injection. Below 100oC, it can be dried without losing the wood.
(9) Pressurized injection method: The dry wood is placed in an injection tank (iron horizontal cylinder) and the agent is injected under pressure. This is the most reliable method. Oily, oil-soluble, and water-soluble agents are all applicable. According to the front operation method, it can be divided into the following three methods:
[Cell filling method (white sun road method)] First, exhaust the air for 30 minutes at a pressure of more than 500 mmHg (exhaust first), then fill the liquid medicine, and inject the liquid medicine into the wood at a pressure of 4-15 kg/cm2. After injecting a certain amount of liquid medicine, restore the normal pressure, and after the liquid medicine is discharged, perform the rear exhaust at more than 500 mmHg. The first exhaust is to remove the air in the wood, which makes it easier for the liquid medicine to penetrate. The rear exhaust can recover the excess liquid medicine and make it easier to handle the injected wood. However, when using water-soluble agents, the rear exhaust can be omitted.
【Empty Cell Method (Rubingu Method)】Pre-operation: After air is compressed into the tank (3-5 kg/cm2), it is then pressurized and injected. The process is the same as the filled cell method. The purpose of air compression is to save reagents. This method is mainly applicable to oily and oil-soluble reagents.
【Half-empty Cell Method (Royal Method)】No pre-operation is performed, and the process is the same as the filled cell method. The injection volume is between the first two. (10) Liquid decompression method: First add wood to the tank, then add liquid medicine, and then pressurize. Both decompression and pressurization are performed in the tank filled with liquid medicine, which shortens the time to reach the specified pressure. In addition, one pump can be used for decompression and pressure reduction, and the entire device is relatively simple.
In short, the use of good anti-corrosion treatment methods plays a vital role in ensuring the quality of wood and reducing wood losses. Every timber yard worker must master the anti-corrosion treatment methods and do a good job of anti-corrosion treatment, so as to further preserve the wood.
