For regular readers, customers and visitors to my website, I am posting GOST regulations (%) for moisture content of planed dry products. I specially systematized and combined into one table where and in what kind of construction and carpentry work these products are used. see table below.
Humidity standards for planed dry products. Use in construction and carpentry work.
| Planed dry product | Purpose | Usage | GOST | Humidity, % |
| board, block | interior work | production of floors, plinths, platbands, window sills | GOST 8242 |
12 ± 3 |
| board, block | interior work | roof truss system, lathing, counter lathing, furniture | 12 ± 3 | |
| beam, board, block | external works | roof truss system, frame manufacturing wooden structure and its lining. | 15 ± 3 | |
| board, block | other external works | production of fences, cladding of small wooden buildings | 12 ± 3 | |
| solid wood | external and internal works | load-bearing structures - floor beams, floor joists, frames (casing) of windows and doors, etc. load-bearing elements | GOST 4981 | up to 20 |
Simply it looks like this:
It is simply necessary for the customer to check these regulations, because In my opinion:
To check by eye the characteristics declared by the supplier, and accordingly trust the supplier with your money, an action, in my opinion, borders on real madness!
How I carry out a full check of the declared characteristics on the website before delivery to my customers, I invite the reader to visit the entire section of my articles dedicated to each section separately. In which the details and conditions are discussed in more detail: - how the customer should check his supplier of planed dry products.
Study of the characteristics of sections of planed dry lumber, carried out by me before delivery to customers of the TorgLes Moscow website-
The photo shows the customer checking the site's moisture content of the finished planed dry product at the TorgLes Moscow retail space before delivery. The test is carried out with a German needle moisture meter, because... a needle moisture meter gives a minimum error in the measurements taken, i.e. allows you to determine how well the GOST regulations for chamber drying are implemented.
Let's look at why this GOST is needed using an example.
For clarity, I am publishing a photo of the material that I've never been in a drying chamber. Those. The entire technological production cycle was disrupted.
Namely, the board of natural moisture was planed on a machine, disrupting an important technological cycle -chamber drying!
In the photo below, in front of the reader batten section 140x35x6000mm. natural humidity. I marked with red circles the defects due to which this material after processing on the machine, it cannot be used for its intended purpose - laying a finished floor in the house.
Some fragments of this profiled board show significant defects:
| Defects | Cause |
|
Bullying and difficult material. |
the machine blades cannot properly process the surface of the material due to its high, non-uniform humidity |
| - tears of individual fragments of wood on the front part of the board | the machine blades cannot properly process the surface of the material due to its high, non-uniform humidity; |
| - the “comb” from the operation of an unevenly operating machine is very noticeable | the machine cannot properly process the surface of the material due to its high, non-uniform humidity |
| - the tongue is curved and “walks” in size, sometimes larger, sometimes smaller. it is simply not possible to connect the floorboards into a shim groove in the future | This is where you can clearly see that the board was not in the drying chamber, because... the machine cannot properly process thin elements of a profiled board |
| - the rapid process of warping in wood has begun | indicates that the board was not in the chamber at all, because the board began to bend like a "Z" |
In our opinion, the most controversial issue on the Internet. Let's answer this question in detail, based on GOST. Also, based on experience and practical examples, let’s try to figure it out and give logical answers to all the above questions.
Wood moisture content - This is the ratio of the mass of moisture contained in the volume of wood to the mass of absolutely dry wood.
A tree is a living material that grows, sleeps, breathes. Because of this, most indicators in wood change from year to year. And such an indicator as moisture content in wood, as well as the moisture content of dry lumber, changes EVEN throughout the year. This indicator depends on the time of year, the region, and the place of growth.
The moisture content of wood is also affected by the region and place of growth.
When the wood arrives less wet, it dries faster, and the drying process is softer and tears it less.
Transport humidity and furniture humidity obtained by drying.
Sometimes a client comes and says: “I want the moisture content of the timber to be 8%.”
You ask: “For what?”
Answer: “They told me (I read) it would be better.”
Based on GOST 8486-86 and experience, transport humidity is the most optimal humidity for construction. Because at a humidity of 18 +/-2%, lumber does not warp, does not twist, does not turn blue, and is not susceptible to fungal infection. Lumber transport moisture completely justifies its physical and mechanical characteristics in construction.
Also, the belief that timber can be dried to 8% is absolutely false, and no one has ever seen such timber.It is impossible to dry the timber to less than 20%, and no one argues that the top layers can be dried to a moisture content of less than 20%, but what about the core? The moisture content of the timber in the core reaches 20%, which corresponds to GOST and DIN. At this humidity, the timber and boards do not warp, do not twist, do not turn blue, and are not susceptible to fungal infection.
There is also interesting data that is included in the table below.
Based on the data in the table, the equilibrium moisture content of wood is 17-18.5%, based on average statistical data (air humidity 80-85% and temperature +10 C). It is logical that to build a house from timber, a humidity level of less than 20% is simply not needed. Building object nothing will “gain” from this.
You can, of course, hear the argument about laminated veneer lumber; it is dried to a moisture content of 8%.
In principle, this is where laminated timber came from Bad quality. They dried it poorly, because it’s not easy to dry a board, not to mention timber, to a moisture content of 8 +/-2%, they didn’t dry it completely, they cheated, and over time the timber can dry out and the lamellas fall off.
Clients also come who say that we demolished my grandmother’s house, and we were never able to disassemble it. The roof “moved off”, but the frame remained rooted in place.
And the client sums it up with an exclamation: “They built it!”
Of course, before no one was chasing to build as quickly and cheaply as possible, no one was chasing “new technologies”. And they cut down the tree, debarked it, gave the log time to mature, and then just collected it.
How is it working out now? Everything is done exactly the opposite. The client wants faster and cheaper, the manufacturer gives what the client is willing to pay for. Here is the overall result.
The desire to obviously save money spoils the opinion about the best natural construction material. Wood, we repeat, is a living material; it “survives” only in the hands of professionals.
The moisture content of wood is great importance to understand further behavior wooden products during operation. Wood is a living material consisting of cells, and cells, as we know, cannot live without water. There are such concepts as free moisture , which is contained in the pores and capillaries of wood and bound moisture , which is contained mediocrely in tree cells. On the border of these concepts is fiber saturation point - this is the wood moisture content at which all free moisture has been removed from the wood, i.e. There is no water in the cavities of the wood, but all the bound moisture remains, i.e. cells are saturated with water. The moisture content of wood at the saturation point ranges from 22 to 35% depending on the type of wood and for practical calculations is taken equal to 28%.
It is important to know: wood changes its physical dimensions at humidity from 0% to the saturation point. Further moistening does not lead to a significant increase in size. The moisture content at the fiber saturation point is higher than equilibrium humidity. Equilibrium moisture content is established in the wood naturally during operation, depending on temperature and relative humidity, so the wood dries out.
For Minsk, the relative average annual air humidity is 78% , in autumn-winter 80-90%, in spring-summer 65-75%. Thus, when drying wood naturally, its humidity is set at 12-15% in summer and 18-20% in winter. It follows from this that when wood products are used outdoors, they change their geometric dimensions throughout the year depending on temperature and humidity. Getting wet from rain can increase the wood's moisture content well above its saturation point. It is also worth noting that when humidity is above the saturation point and warm weather Ideal conditions are created in the wood for the development of tree-destroying fungi. The limit of biostability of wood is considered to be a moisture content of 22% . Therefore, when operating on the street in the conditions of the Republic of Belarus.
The main rule for using wood: Before installation, the wood must have the moisture content in which it will be used in the future. . This rule also applies to other materials - WPC, laminate, plywood, etc. Thus, before installation, the wood should be left for some time in the conditions of the environment in which it will be used.
The main types of wood used in construction in Belarus are pine and spruce. The volumetric shrinkage of these rocks from freshly cut to dry is up to 15%, the change in size across the grain is up to 10%. Knowing this rule is very important when installing lining, imitation timber, block house, floorboard, especially when using raw or very dry materials.
When drying wood in air, the time of year, wind direction, temperature regime, material cross-section and other factors. Therefore, the time it takes to reach equilibrium wood moisture content is natural drying can only be predicted. According to these parameters, during the Soviet era, Belarus was classified as the 3rd conditional zone according to GOST 3808.1-80 and the following period for drying lumber naturally was determined: 
According to the table, in Belarus natural drying is possible only from April to September. This is not true, because drying occurs even at 100% relative air humidity and a temperature of 0 degrees. Thus, from October to March, being outside, the wood also dries.
To understand what moisture content wood has after autoclave impregnation, we will present some numbers and calculations.
Thus, after autoclave impregnation, the wood moisture content is approximately 65%. This is the moisture content of freshly sawn wood. Hence natural drying times to operational humidity can be approximately determined from the second table at the top of the page.
Wood moisture content is a value that shows the level of moisture exchange between wood and air. Since the humidity of the environment is variable, it is constantly changing in wood. The level of this indicator affects the quality and use of lumber. Products with high humidity more susceptible to mold and mildew, rotting and deformation. Therefore, dry raw materials are chosen for the construction and manufacture of wooden products.
Humidity can be absolute or relative. The first represents the ratio of the mass of moisture in wood to the mass of absolutely dry wood. A more commonly used, convenient and easy-to-calculate quantity is relative humidity. This is the ratio of the moisture mass of wood to the total mass of wood, which actually reflects the water content in the product. This value is decisive, so it is used in practice.
The initial figure is usually 50-60%. With natural drying, after 1.5-2 years it drops to 20-30%, after which it does not change much and remains at approximately 25%. There are wet wood with a moisture content above 35%, semi-dry wood with a moisture content of 25-35% and dry wood with a moisture content of less than 25%. To reduce the moisture level to room-dry 7-18%, lumber is dried in special drying chambers.
The following types are distinguished:
To build a house or bathhouse, dry lumber with a moisture content of up to 20% is used. Today the safest and effective method, which allows you to achieve such indicators, is condensation drying. When drying, both hot and cold air. This prevents the appearance of defects and defects on the log or timber, reduces the number of cracks and allows you to obtain high-quality, durable and dry lumber. Read more about condensation drying.
In “MariSrub” you can order construction wooden houses only from high-quality and carefully selected dried materials. We independently produce logs and beams for the design of a wooden house, bathhouse, gazebo or garage. Choose custom design or customization already ready-made version which you will see in .
During production we use condensation drying, we comply with GOST requirements, storage and transportation standards. We carry out antiseptic treatment and control every stage of production, which allows us to obtain durable and high-quality lumber. Due to this treatment, the wood retains its original color and natural properties for a long time. It does not rot or darken or become moldy. The materials are resistant to moisture and cold, wind and insects, and temperature changes.
We are building wooden houses from timber and logs from the manufacturer. Own production is a guarantee of quality and low prices for lumber! We offer turnkey construction, which includes the creation of a project and installation of timber or log house, construction of the foundation and roof, finishing inside and outside the house, installation and commissioning utility networks. We guarantee quality construction on time!
Wood is a very hygroscopic material that easily changes its humidity. The moisture content of wood is the percentage of water (moisture) in it. The moisture content of wood does not depend on the type of wood. Wood moisture content is a quantitative indicator of the moisture content in it
Moisture exchange occurs all the time between wood and air. Therefore, the moisture content of wood is a very unstable value, which changes along with the humidity of the environment. If the humidity of the wood is greater than the humidity of the surrounding air, the wood will dry out. If it's the other way around, it's hydration. And if the humidity and temperature of the environment (air) remain constant for a long time, then the humidity of the firewood will also stabilize and will correspond to the humidity of the surrounding air.
The moisture content of wood at which the exchange of moisture between it and environment, called “equilibrium”
In nature, equilibrium moisture content for wood is an extremely unstable state. Because in nature it is impossible to find air with constant temperature and humidity parameters for a long enough time. However, the state of equilibrium humidity is easily achieved for wood located in an artificial microclimate, for example, in a drying chamber or simply in any other room with constant temperature and humidity.
Distinguish between absolute and relative humidity of wood
Absolute humidity is the ratio of the mass of moisture that a wood sample contains to the mass of absolutely dry wood of the same sample. According to , the value of absolute humidity (W) is calculated after examining (drying) the sample, according to the formula:
W = (m - m 0) / m 0 x 100,
where (m) and (m 0) are the mass of the sample before and after drying.
The concept of the value “absolute humidity”, according to GOST 17231-78, is interpreted simply as “humidity”. Like everything “absolute”, the value of “absolute humidity” is divorced from the real world and is an extremely indigestible form for thermotechnical calculations. For example, at an absolute humidity of 25%, a kilogram of wood will contain 200 grams of water. This discrepancy in numbers confuses calculations.
The relative humidity value is more convenient and practical
Relative (working) humidity of wood is the ratio of the mass of moisture that a wood sample contains to its total mass. According to GOST 17231-78, the value of relative humidity (W rel.) is calculated from the value of absolute humidity (W) of the sample, according to the formula:
W rel. = 100W / (100+W)
or more simply,
W rel. = m water / m sample x 100
Relative humidity is a very simple and convenient form for taking into account evaporated water in wood-burning heat engineering calculations. The value of relative humidity directly indicates the quantitative water content in wood. For example, one kilogram of wood with a moisture content of 20% will contain 200 grams of water and 800 grams of dry wood matter.
For comparison, let’s put a “live” example into a table. This is a table for the same our sample. Let us determine and compare the values of its absolute and relative humidity:
|
Absolute humidity = 25%, |
Relative humidity = 20%, |
| absolute humidity will be 25%, | - if one kilogram of wood contains 800 grams of dry wood matter and 200 grams of water, then its value relative humidity will be 20%, |
|
Formula for determining W = (m - m 0) / m 0 x 100 W = (1000 - 800) / 800 x 100 = 25% |
Formula for determining W rel. = 100W / (100+W) W rel. = 100 x 25 / (100+25) = 20% |
|
Conclusion Despite the fact that the value of absolute humidity is the primary source for determining the value of relative humidity, it is the value of relative humidity that has a greater practical use. Because it (the relative humidity value) more realistically reflects the water content in the sample and does not confuse the numbers with discrepancies |
|
According to humidity, all wood is divided into three groups: wet (humidity more than 35%), semi-dry (humidity from 25 to 35%) and dry (humidity less than 25%). Initially, the humidity of freshly cut trees is 50-60%. Then, during natural drying under a canopy in the air, the wood loses up to 20-30% of its moisture over the course of one and a half to two years and reaches a state of relative humidity. After this, the moisture content of the wood no longer changes significantly, and its value is ≈25%. Such wood is called air-dry. To reduce the moisture content of wood to a room-dry state (7...18%), it must be dried forcibly in drying chambers, or moved for a long time to an artificial microclimate with specified conditions (for example, moved to a room or other room).
Distinguish the following degrees wood moisture content:
The calorific value of wood is directly dependent on its moisture content. The moisture content of firewood is a determining indicator of its quality. That dry wood burns better than wet wood is known to many, if not everyone. And everyone knows that wet firewood can always be dried, and dry firewood, on the contrary, can be wetted. Accordingly, the quality of the fuel will change - improve or deteriorate. But is this really important for modern heating equipment? For example, wood-burning pyrolysis boilers allow you to burn wood with a humidity of up to 50%, and even up to 70%!
The table shows generalized indicators of the calorific value of wood for each degree of its moisture content.
The table shows that the lower the moisture content of the wood, the higher its calorific value. For example, air-dried wood has a working calorific value almost twice as high as freshly cut wood, not to mention wet wood.
Wood with a humidity of 70% or higher practically does not burn.
Perfect option for wood heating is to use firewood at a room-dry humidity level. Such firewood provides the maximum amount of heat. But, since drying firewood to such a state is associated with additional energy costs, the most the best option For heating, air-dried wood will be used. Bringing firewood to an air-dry state is relatively easy. To do this, it is enough to prepare them for future use and store them in a dry, ventilated area.
Finally, I would like to note that the moisture contained in firewood not only worsens its calorific value. Increased content moisture in the fuel negatively affects the combustion process itself. Excess water vapor serves as the basis for creating an aggressive environment, which causes premature wear of the heating unit and chimneys.
Manufacturers of modern heating equipment recommend using air-dry wood as fuel, with a humidity of no more than 30-35%
