Wood defects and methods of protection

When building a wooden house, it is necessary to take into account that various defects are inherent in wood, but some of them are marked as permissible in building codes and standards:

1. Rot and surface wormhole on the survey parts – only for category 3 materials;

2. Knots (except rotten and tobacco), while the distance between the whorls should be at least 400 mm, in addition, at a length of 200 mm, the sum of ¼ of all knots on the edge should not exceed ? parts of the corresponding side of the element;

3. Tobacco and rotten knots measuring 20-50 mm, but not more than one per linear meter.

4. Stepsons;

5. The slope of the fibers is within 7-10%;

6. Cracks are not allowed;

7. The core is allowed in bars whose thickness is more than 60 mm.

Some defects can be avoided or reduced to acceptable values by using simple atmospheric drying. Two methods of laying lumber are used: in ordinary and batch stacks. Horizontal ditches are arranged in stacks.

Lumber subject to atmospheric drying in the heat season should be stacked on the first day after sawing, as they are affected by mold and blue in dense packages. The duration of drying depends on the time of year and the size of the cross-section of the material.

It should be borne in mind that the most dangerous biological destroyers of wood are mushrooms: real house mushroom, white house mushroom and filmy house mushroom. All house mushrooms cause destructive rot, characterized by the presence of longitudinal and transverse cracks in the affected areas of wood, resulting from the destruction of cellulose.

A real house mushroom is especially dangerous, as it is able to develop in dry wood, it remains viable for several years in a dried state. Developing when moistened, it forms large cotton-like clusters, gray interweaving of cords and strands, and then an oblong egg-shaped body, which has a brown color and a whitish frame.

The white house mushroom also forms a mycelium, cords and spongy fruit bodies of white color on the surface of the wood. However, it can only exist on wood with high humidity.

The filmy house mushroom has a mycelium, cords and fruit bodies of dark color. It develops only at very high humidity of wood.

Among insects, the more dangerous destroyers of wood are the woodworm beetle or the black house barbel, the furniture grinder, as well as the tree gnawer.

To protect wood from biological destroyers, antiseptic aqueous solutions are used: 3% sodium fluoride, 5% iron sulfate, 15% copper sulfate. Any of these solutions at a temperature of 800C is applied to wood with brushes or sprayers. After drying the surface, the operation is repeated.

Pressure impregnation is used for large elements that are subjected to a stable leaching effect of water, or located in damp soil. Impregnation is carried out in autoclaves with water-soluble or oily antiseptics. The wood needed for impregnation is dried to a humidity of no more than 25%.

Impregnation in hot and cold baths is carried out with both oily and water-soluble antiseptics. Wooden elements are impregnated, which are in conditions of imminent periodic moistening or constant moistening with ground water. For impregnation, the elements are immersed first in a very hot bath from 20 minutes to 2 hours, then for the same period in a bath with a very cold antiseptic. The temperature of hot baths should be 95-100 °, and cold 20-25 ° with water-soluble antiseptics, and 50-60 ° with oily antiseptics.

The duration of impregnation depends on the dimensions of the elements. Full impregnation is suitable for sapwood; for sound wood, impregnation is not suitable.

High-temperature hot-cold baths are used for synchronous impregnation and drying of wooden elements that allow protective treatment with oily antiseptics. Raw wood is dried in a bath with petrolatum. It is a mixture of solid hydrocarbons with highly viscous refined oils. It is obtained in the production of aviation oils, which melt at a temperature of 50 - 60 °.

During the first drying period, the petrolatum is heated to 110 - 120 °, then the temperature rises to 125 - 140 °.

One hour before the end of drying, the bath temperature is raised to 140 - 150 °. When the wood is heated, a gradual increase in the elasticity of the vapor-air mixture occurs, moisture moves from the inner layers of the wood to the surface and disappears in the form of steam, and the petrolatum foams very violently. The end of the entire drying process is cleaning the bath mirror from the foam and stopping the release of some steam bubbles.