“Hostile whirlwinds are blowing over us” or What will protect the wood from enemies and pests. Drying and protective treatment of wood

By absorbing and releasing water molecules in the molecular structure of wood, it swells when it absorbs moisture and shrinks when it leaves. Due to the anisotropy of wood, the values ​​of shrinkage and swelling are different in three main directions.

Based on empirical data, you can focus on the following values:

Tangential direction (in the direction of annual layers) - about 10%;

Radial direction (in the direction of the medullary rays) - about 5%;

Longitudinal direction (along the fibers) - approximately 0.1%.

In this case, shrinkage and swelling occur in proportion to the change in wood moisture content. Table 1 shows, as an example, the different shrinkage values ​​according to DIN 68100 for some types of wood.

1 Calculation method from tangential and radial values ​​to the annual ring, respectively, to the growth zone.

According to DIN 1052-1, there are calculated values ​​for shrinkage and swelling values ​​(Table 2). For certain tree species, in most cases, a calculation based on tangential and radial values ​​is used, since the actual boundaries of tree rings in a wood section are unpredictable.

Swelling and shrinkage of wood and wood materials have, of course, great importance For paint coating, since the coating must maintain adhesive strength (adhesion) and elasticity (prevent cracking) when the size of the wood changes.

Wood hardness

Other important technological property wood is its hardness. Hardness is defined as “the resistance of a material to the penetration of a foreign solid under the influence of external force" Determination of wood hardness is mainly carried out by the Brinell ball hardness test (BH) with a moisture content u = 12% (DIN EN 1534). Determination of hardness is influenced by bulk density, grain direction, proportion of early and late wood, lignin and resin content, and moisture content. The HB value for spruce, for example, is 1.2 perpendicular to the grain direction and 3.2 along the grain. Hardness, and the choice of wood, plays with it important role especially for paint and varnish coatings on floors and parquet. Brinell hardness undoubtedly indicates possible damage to the floor and paintwork from heels. Thus, according to Emmler's report, deep indentations from heels are found on floors with a Brinell hardness of less than 25 MPa, while on the laminate, on the contrary, no marks remain.

When purchasing wood, we are usually interested in its moisture content. No one wants to buy raw lumber because its use as construction or ornamental material justified only in rare cases (for example, for pouring concrete).

Therefore, logging and wood processing enterprises usually trade in wood that has already undergone the drying process.

What is wood moisture content

In production construction work and for the manufacture of wooden products, wood with a moisture content of no more than 23% is usually used.

• wet – humidity more than 23%;
• atmospheric-dry – humidity 18 – 23%;
• air-dry (after artificial drying) – humidity 12 – 18%;
• room-dry – humidity 8 – 12%.

The lower it is, the less susceptible it is to rotting. In addition, after drying, almost all properties of wood that are important for use are improved:

• its strength increases;
• deformability decreases;
• , sanding, gluing, painting;
• indicators such as electrical conductivity and heat capacity decrease, the calorific value increases;
• The density of wood is directly related to its moisture content; the drier the wood, the lighter it is.

There is also the concept of equilibrium moisture content of wood. This means that at certain values ​​of air humidity and temperature, the moisture content of wood remains unchanged and tends to a certain value.

If these parameters change, the wood will either release moisture into the surrounding atmosphere or absorb it until the humidity reaches a new certain value.

Thus, during the drying process of wood, its moisture content is deliberately reduced to equilibrium values, depending on where and how the lumber will be used.

Wood drying methods

All ways excess moisture can be divided into the following types:

• natural drying;

The first method is known to everyone. It consists of putting the lumber in a stack, where the rows are interspersed with spacers, putting a covering on top to protect it from precipitation, and leaving it to lie in the air. Due to constant ventilation of the stack, the wood loses moisture and dries out.

The second method is to dry the wood in special drying chambers Oh, where you can regulate the air temperature and humidity. But this option is suitable for drying and is used mainly in woodworking enterprises.

What methods of drying wood can you use at home?

Even the ancient craftsmen knew how to perfectly dry wood to the desired condition. Many methods were used for this, some of which are still relevant today.

There is such an unpleasant property of wood as cracking when drying. However, not all types of wood are equally susceptible to cracking:

• alder, linden, birch, poplar and aspen - dry almost without cracks;
• larch, spruce, cedar, fir, pine - crack, but not too much;
• beech, hornbeam, maple, ash, oak are subject to severe cracking.

This is a circumstance for drying each type of wood.

One of the well-known folk drying methods is drying the tree directly on the root. It is carried out as follows:

• At a distance of about half a meter from the ground, the bark is removed in a ring along the entire circumference of the chosen trunk. The width of the ring is approximately 1 - 1.5 m. Reducing the width of the ring leads to an increase in drying time.
• The removed bark stops the flow of moisture into the tree crown, while the foliage quickly consumes the remaining moisture in the trunk, thereby dehydrating it.
• The readiness of the wood is determined by the degree of drying of the foliage.
• When it is completely dry, the trunk can be cut down and used.

Drying the cut trunk:

• The tree is cut down and, leaving a ring of bark on the trunk 0.7 - 1 m wide from the point of cutting, the rest of the trunk is left without bark. The crown is not touched.
• The foliage remaining on the trunk quickly draws moisture from it, effectively drying out the wood.
• After 2 - 3 weeks, the trunk can be sawed and folded under a canopy for final drying.

Drying is carried out in the same way as in enterprises: a flooring is built on a flat, dry area, on which lumber is stacked. The top row is laid with a slope and covered from precipitation.

To protect the ends of the material from rotting, they are covered with lime and treated with a solution table salt or coated with liquid glue.

This method allows you to get rid of 75% of the moisture in the wood, but is very slow:

• coniferous and soft hardwoods dry out within 1 – 1.5 years;
• hardwoods – more than 2 years.

Drying wood in a closed, ventilated area. To do this, you can use a spacious barn or a fairly high attic. Here there is a stack of wood laid on pads than on the street. It is only necessary to ensure constant ventilation of the room.

Drying lumber on a cement floor. This method is sometimes used to dry small volumes of lumber. It is laid out in one row on a cement floor and the boards are turned over from time to time. The method is based on the ability of cement to draw moisture from other materials upon contact.

Drying small wooden blanks and details using newspapers:

• the workpiece is wrapped tightly in dry newspaper and placed in plastic bag which is wrapped tightly.
• The bag with the workpiece is placed in a warm place.
• When the newspaper becomes damp, it is replaced with dry one and the process is repeated until the workpiece reaches the required humidity.

This process usually lasts about 3 – 4 weeks. As the wood dries, newspapers have to be changed less and less often. To speed up the process, the workpiece can be wrapped in a thicker layer of paper, but here too fast drying can lead to cracks.

Drying workpieces using sawdust or straw: the workpieces are covered with a thick layer of sawdust or dry straw and placed under a canopy. Sawdust and straw take moisture from the wood, but there is no need to change them, they quickly dry out on their own.

Drying by steaming and boiling wood.

These are more complex methods, but they can be successfully used at home.
The steaming method is used to replace the moisture contained inside the wood with vegetable oil. To do this, the workpiece is placed in a container with any vegetable oil and heat over low heat for 6-7 hours.

The steaming time depends on the size and thickness of the workpiece. In former times, wood intended for making wooden utensils. And the dishes turned out to be very durable, without cracks.

The digestion method involves keeping the workpiece for a long time in a boiling salt solution (2 tablespoons of salt per 1 liter of water). Salt expels cell sap from wood, replacing it. Myself saline solution is expelled from wood much faster than water and without “severe consequences.”

After boiling for 8 - 10 hours, the workpiece is removed, tied with a rag and placed in a dry place for 2 weeks. When using boiling, you can simultaneously change the color of the wood. To do this, pine sawdust is mixed into the saline solution. If the workpiece has big size, then after drying in air, the digestion is repeated, then the workpiece is dried again. All this time the harness is not removed from her.

If the products were made from damp wood, they can be dried using dry, clean river sand. To do this, the workpiece is placed in a container of suitable size, sprinkled with sand on all sides and placed in the oven.

We looked at the best ways to dry wood at home. They all require time and patience. So if you urgently need a dry blank or several boards, then it would be more advisable to purchase blanks of the required moisture content.

If you are a home craftsman and you have nowhere to rush, traditional methods drying will be just right. After all, they almost 100% guarantee proper drying of the wood, in which the risk of cracks is minimal.

Why are several of them put together in the title of the article? Very simple - how shrinkage, so swelling cause not only changes in size but also warping wood

Already at the stage of harvesting lumber, we obviously receive boards that will warp during drying. This occurs due to the uneven drying of the layers of wood. Layers further away from the core dry faster. Therefore, warping occurs in a “boat” manner, and the middle boards have almost no warping, but towards the edges the boards become noticeably thinner. This defect is eliminated by jointing and drawing parts to the required thickness, as well as by gluing panels from narrow strips of wood. (There are many more various types warping of wood, but the principles for eliminating them are almost the same.)

During drying, the dimensions of the parts change. The average value of these changes is approximately equal to:

• along the grain — 0,1 — 0,3 %
• across the grain (in the tangential direction) — 6 -10%
• across the grain (in the radial direction) — 3 — 7 %

But these values ​​are valid only for shrinkage from the fiber saturation point to absolute value, i.e. for complete drying.

But have you noticed that light stripes appear on your doors along the edges of the panels in the summer, and in the fall they disappear. This suggests that wood, even coated with varnish or paint, still reacts to changes in humidity in environment. The tree "plays". And it will play for the rest of your life.

We will talk about how to avoid the appearance of these stripes when we talk about making doors.

Of course, the carpenter does not need to know exact numbers, by how much does the width of a particular part decrease? But when making furniture from solid wood, you need to understand the meaning of drying out and warping. You need to understand that you shouldn’t rely on modern glues and screws, as many carpenters do. Just as no amount of asphalt will stop the roots of a growing tree, no block tightly screwed to the bottom of the tabletop will save it from bending. After all, a decrease in size in the transverse direction, as we wrote above, in 10-12 times more than in the longitudinal one. So the old masters used the “dovetail” for inserting bars into the tabletops, as well as the “floating” method of attaching them to the table frames.

And frame structures are less susceptible to warping and deformation than large glued panels.

I also saw torn doors and other paneled structures. This was precisely the result of the swelling of the panels. An inept or inexperienced craftsman forgot to give free rein to the panels when assembling the doors, or even, thinking that he would thereby strengthen the structure, gave them stickers.

Freshly cut wood usually has a moisture content of 50-70%, and lumber after sawing logs - 60-75%. Wet wood is easily chopped, chipped, and bent. At the same time, it is heavy and weakly holds metal fastenings; it is difficult to saw, plan, or drill. It cannot be glued or finished; in the absence of good ventilation it quickly rots. Products made from raw wood change size and shape as they dry, tenon joints dry out and weaken.

Drying wood increases its mechanical strength; bonding strength of units and parts; possibility of finishing; stops the vital activity of fungi and eliminates the possibility of their appearance; reduces the weight of products.

During the drying process, moisture evaporates primarily from surfaces in contact with air, a difference (difference) in the humidity of the outer and inner layers occurs, and moisture moves from the inner to the outer layers. First of all, free moisture evaporates and moves from the inside to the surface, then (much more slowly) bound moisture. The rate of evaporation and movement of moisture depends on the type of wood, the size of the material being dried, and the drying conditions.

If wet wood enters a room with dry and warm air and at the same time, the slow-drying species is dried in the form of thick boards or bars, then moisture from the surface layers of wood will evaporate much faster than it will flow from the inner layers to the outer ones.

When the humidity of the outer layers drops below 30%, their drying begins. At the same time, the inner layers with a humidity above 30% retain their volume. As a result, tensile forces arise in the outer layers, and compressive forces occur in the inner layers. If tensile forces more power adhesion between the fibers, breaks appear in the form of external cracks.

In the next stage of drying, when the moisture content of the inner layers becomes less than 30%, their size and volume decrease under the influence of shrinkage.

Due to the fact that in the first stage of drying the outer layers dried relatively quickly and were in an extended state, the amount of their shrinkage will be less than that of the inner layers that dry more slowly and are in a compressed state. As a result, compressive stresses will arise in the outer layers, and tensile stresses will arise in the inner layers. The latter will cause the appearance internal cracks. Shrinkage of the outer layers is called hardening of the outer surface of the wood and is also a serious drying defect.

To avoid these defects during drying, it is necessary to create conditions such that the rates of evaporation and movement of moisture inside the material are the same. As the air temperature rises, the movement of moisture in the wood accelerates, and with an increase in air humidity, the rate of moisture evaporation by the surface layers of the material decreases. Thus, it is possible to select combinations of temperature and air humidity at which the appearance of harmful stresses in the material will be excluded.

Different types of wood dry differently. Some are more susceptible to warping and cracking, others less so. Boards and bars of large sections require longer drying times than smaller ones. In this regard, in each specific case, a certain drying mode is established depending on the type of wood, the thickness of the material, as well as its purpose and quality requirements.

There are two main ways to dry wood: drying outdoors(natural or atmospheric) and in special drying chambers or dryers (artificial or chamber drying).

During atmospheric drying, lumber is placed in stacks (7) in rows, between which spacers should be placed. The boards in each row are laid at intervals equal to a quarter or half the width of the board. The stacks are placed on concrete or wooden foundations. The top of the stack is covered with a shed or gable roof. To protect against cracking, the ends of the lumber are coated with a lime or chalk composition, and the boards of each overlying row are placed so that they create a shadow for the ends of the boards of the underlying row. Area

the warehouse must be of sufficient size to accommodate stacks with the required number of aisles and driveways between them; be open and accessible to the prevailing winds in the area, sufficiently high, clean and dry.

Air drying is the simplest, but at the same time very long process. The drying time depends on the type of wood, the thickness of the lumber, the time of year and climatic conditions of this area. On average, for the central regions of the RSFSR, Ukraine and Belarus, the drying time for coniferous boards with a thickness of 35-50 mm can range from 20 to 60 days. The method requires large areas to accommodate the warehouse. But the most significant disadvantage of atmospheric drying is that the moisture content of the wood cannot be less than the humidity equilibrium of the environment, i.e. 15-20% (air-dry state).

These disadvantages are completely eliminated by chamber drying. You can dry wood in the chambers at any time of the year and quite quickly (within 3-8 days). In this case, the wood is rendered harmless, since when high temperatures(60-80°C and above), the spores and mycelium of wood-decaying fungi, as well as insects - wood pests, die. Chamber drying allows you to dry the material to a moisture content of 12-8% and below, which is especially important for carpentry work.

In woodworking workshops that do not have drying chambers and process small quantities wood, lumber is usually laid for some time in the open

air for preliminary drying, bringing their humidity to an air-dry state, and then they are dried (in the form of rough blanks) indoors on specially arranged racks, under which air heaters are installed. A hood is installed above the shelves to remove damp warm air.

Drying wood in ridges, used, for example, for monumental or easel sculpture, is particularly difficult. If the bark is removed from the ridge, the evaporation of moisture will occur with large surface exposed to direct air, and much faster than the movement of moisture from the inner layers to the outer. As a result, there will be a large difference in humidity between the inner and outer layers of wood. As a result of this, as well as greater shrinkage of the wood along the length of the annual layer than in its thickness (while maintaining the size and volume of the wetter wood of the central part of the ridge), tensions arise in the wood of the outer layers, which cause ruptures in the fabric of the outer layers. Since the connection or cohesion of the fibers along the length of the growth rings (along their circumference) is weakened by the presence of pith rays, these breaks occur in the direction from the sapwood to the pith (8, a).

When drying a ridge with bark (8, b), moisture evaporation occurs mainly from the surface of the ends, the wood of which dries out more in the central part than on the periphery, protected by the bark. As a result, the reduction in the length of growth rings in the central part of the ridge will occur more intensely than the reduction of rings located near the crust. This will cause the formation of cracks in the central part of the ridge, located, as in the first case, in the radial direction. In the bark, the core cracks will be thin, and in the middle part along the radius of the end they will be wider.

To avoid these defects, it is necessary to create conditions such that the evaporation of moisture from the end and side surfaces of the ridge occurs at approximately the same speed and as slowly as possible. To do this, you must first close the ends of the ridge - paint them oil paint or putty made of clay and drying oil. It is advisable not to remove the bark, but to make transverse cuts on it with an ax (9, a) to give air access to the wood. If the ridge is short, then the bark is removed in its middle part, leaving rings 20-25 cm wide at the ends (9, b).

The ridges need to be dried gradually, first outdoors under a canopy, then in an unheated but dry room, and finally in room conditions(for easel sculpture).

Protective treatment of wood is carried out in order to protect it from rotting, insect damage and rapid combustion. To protect against fungal damage, the wood is impregnated or coated with antiseptics - substances that can kill fungi and prevent their development in the future. Treatment with these substances is called antiseptication.

Antiseptics are divided into water-soluble and oily, soluble in organic solvents.

Water-soluble antiseptics are powdery or crystalline substances of mineral origin, used in the form of 3-6% aqueous solutions. The most common of these are sodium fluoride and sodium pentochlorophenolate.

Of the oil- and organic-soluble antiseptics, the main one is pentachlorophenol - crystalline substance yellowish-gray color. It is very toxic to wood-decaying fungi, insects and woodworms, chemically quite inert, non-volatile, and practically insoluble in water, but soluble in many organic solvents of petroleum origin. Solutions of psntachlorophenol in light volatile solvents are used for impregnation of joinery products. At the same time, the wood is well glued, painted, and polished.

Fire protection of wood is carried out by impregnation with chemicals called fire retardants. These substances melt when heated and cover the surface with a fire-retardant film, stopping the access of air oxygen to the wood, or decompose and release large quantity non-flammable gases that displace air. As a result, the wood smolders, but does not burn.

Ammonium salts, phosphoric and boric acids and their mixtures are used as fire retardants. Impregnation of wood is carried out in impregnating cylinders under pressure.

To protect wood from fire, it is painted with fire-retardant paints. Most often used silicate paints based liquid glass. They are applied with a brush in two steps with intermediate drying for at least 12 hours.

Paints are usually white and completely cover the wood texture.

Measures that increase the durability of wood also include finishing finished products: painting, varnishing, polishing, etc.

Wood is stored in the form of sawn timber (boards, bars) or temporarily as whole logs. Before storage, be sure to remove the bark from the logs, under which woodworms multiply or fungus appears, which spoils the entire stack. Logs cut in summer are cleared of bark two weeks after cutting, and logs harvested in winter are removed before the weather warms up.

At the ends of the logs, strips of bark 10 cm wide should be left, due to which the ends are less likely to crack. It is very convenient to peel bark from a log with a shovel cut so that the end is slightly oval. You can use a large army shovel, it is durable and heavier than usual. When logs or lumber dry out, the moisture from them evaporates more through the ends and cracking of the wood begins precisely from them. Therefore, the ends should be covered with bitumen, pitch-resin mixture, grease, or painted over with oil paint, clay with lime or mullein, clay or a thick solution of lime.

Store lumber and logs in stacks, installed on poles, stone or concrete stands - stackers 50-65 cm high. Pieces of roofing felt are placed on them for waterproofing, and then strong crossbars, on which lumber is laid, preferably of the same size in thickness, width and the same species. Boards or bars are laid between the layers of ventilation logs. The top of the stack should be protected from exposure to direct sun rays and roof precipitation. The distance from the top row of timber to the roof is 12-15 cm, so that the air from above does not linger under the roof.

Lumber, if there is little of it, is best stored indoors under the ceiling. To do this, crossbars are attached to the ceiling, and first long and thick boards or bars are placed on them, and then short ones.

Wood for most building structures and furniture making must be dried. When wood dries, its dimensions across the fibers decrease by 5-12%, and along them almost do not change. Therefore, in a product made from damp or under-dried wood, after some time cracks or crevices appear at the joints.

Drying

Drying can be natural - in stacks and artificial - in dryers.

Natural drying always takes quite a long time. Logs dry for a year or two, depending on the diameter, and sawn materials - from 10 days to two months, depending on the thickness of the boards and the time of year.

At natural drying it is forbidden

Get wood with a moisture content of less than 16%, so it is used only for building structures. To make furniture and lay floors, you need wood with a moisture content of no more than 10%. To do this, it is dried in chambers that are heated and well ventilated.

At home, you can dry the wood indoors during the winter. You just need to do good ventilation so that moisture is removed from the room after the wood has dried. The amount of wood shrinkage depends mainly on its density. Soft wood dries less hard. Beech, hornbeam, birch, larch, and pear dry out very much. Conifers dry out less than deciduous.

The sapwood (outer layer of the log) dries out more, than the core, so the boards bend towards the sapwood when drying.

When making panels (for doors, etc.), the boards with the sapwood side are returned to different sides so that the product does not bend when drying.

In general, the wood in the product “breathes” - its volume decreases from dry air and increases when moistened. As a result, cracks appear in the products, joints in the tenons are broken, etc. Therefore wooden crafts It is recommended to dry and paint on all sides to protect the wood from moisture.

Trees that grew singly or at the edge, in cross section have annual rings of unequal width - with south side they are wider. Therefore, boards made from the south side of the log warp more when drying than those from the north. That is why it is recommended to place the log on the pit with the wide part of the rings up or down. Then all the boards will have wide and narrow annual rings and dry evenly.

Special processing

Wood is treated to protect it from rot (fungus), wood-eating insects (shashel) to provide it with fire resistance. Protect wood from the fungus, which mainly affects poorly ventilated and damp parts of buildings, using water-soluble or oily antiseptics.

The water-soluble antiseptic has the following composition, parts by weight:
sodium fluoride…… 3.0
dye ………………… 0.05
water…………………………… 97

Sodium fluoride and dye are dissolved in hot water(80°C). Instead of sodium fluoride, you can take sodium fluoride or ammonium fluoride. The dye is needed only to control the uniformity of wood processing. It can be aniline fabric dye or even ink.

It is better to soak the wood in baths for 20-30 minutes. If there is no bath, then the solution is applied to the wood with a large brush 3-4 times after the previous application has dried.

You can also treat with a paste of this composition (antiseptic), mass parts:
sulfite-alcohol stillage…. 1, 2-2

sodium fluoride…. 1-3

peat dust…… 0.2-0.3

water……………………. 1.6-2.2

This paste is used to coat the wood with a brush at the rate of 400-750 g per 1 m2 of surface. Both given water-soluble compounds are used to treat wood that will be exposed to water, otherwise the antiseptic will be washed out.

Oil antiseptic is more resistant to moisture, has the following composition, mass parts:
petroleum bitumen grade 3-4 .. 1.5
green oil (petroleum bitumen solvent) ……………. 0.35
peat dust………….. 1.5

335-350 g of paste is consumed per 1 m2 of wood.

You can protect wood from worms with a solution of chlorophos (10%), a saturated solution of sodium fluoride, a solution of naphthalene in gasoline, a mixture of turpentine and kerosene (3:1), as well as borax and boric acid(1:1) concentration 10-20%. This solution simultaneously makes the wood fire resistant.

Pillars that are buried in the ground are protected from rotting by firing to a depth of 1-1.5 cm and the length is 15-20 cm greater than the burial depth. Coat the well-burnt area with used engine oil or molten bitumen and wrap it in roofing felt or roofing felt, which is secured to the pole with wire.

Should be paid Special attention to that part, which protrudes from the ground. Here the wire is tightened very tightly so that the water along the trunk does not flow behind the insulation, but flows like this.

Liquid solutions are applied to the affected product with a brush. If there are few holes in the wood, then you can inject the solution into them with a syringe.

To make wood fire-resistant, it is also coated with liquid, mass parts:
ammonium sulfate ………… 4
brown…………………………….. 1
water …………………………… 15

Before dissolving the components in it, the water should be heated to 70 ... 80 ° C.

Wood becomes acid-resistant if it is successively treated with the following solutions:
aniline hydrochloride…………………. 160

ammonium chloride (ammonia) .... 24

water……………………………………………. 1000

This solution is applied to the wood hot, and after drying it is covered with another solution, g:

copper sulfate……….. 160
Berthollet's salt……. 80
water………………………. 1000

The wood is allowed to dry and again covered with the first and then the second solution, and so on four times. After the last drying, the surface of the wood is treated with fine sandpaper and covered with drying oil. It turns black.