How to measure the moisture content of wood. How to determine whether a planed board is dry or not without having a moisture meter at hand. There are several types of wood moisture

Direct - according to the method, indirect - with the help of electrical ones. The first way is accurate, the second way is fast.

Determination of wood moisture according to GOST 17231-78 (GOST 16483.7-71)

Method one - direct (standard, old-fashioned, time-tested)

On the this moment, on the territory of Russia there are two standards, both regulating the same method for determining the moisture content of wood:

GOST 17231-78 Chipped and round timber.
Moisture determination methods
Download (Downloads: 1226)
GOST 16483.7-71 Wood.
Moisture determination methods
Download (Downloads: 914)

Analogs of these standards can be easily found in the metrology of any post-Soviet country. Both documents (GOST 17231-78 and GOST 16483.7-71) regulate the sampling procedure, test and analysis methods for objectively determining the moisture content of timber, timber and firewood (everything from which a sample can be cut or sawed off for research). The method for determining moisture content in accordance with GOST 17231-78 and GOST 16483.7-71 is extremely simple and consists in the systematic selection and subsequent drying of samples of the test material. In this case, the sample under study is in drying cabinet until it dries completely. After that, weighing and comparison of the weight of the examined wood is made before and after drying.

Approx. According to GOST 17231-78 and GOST 16483.7-71, a sample is considered dry if its mass has not changed by more than 1% after being kept in a drying cabinet for 24 hours at a temperature of 101 ... 103 ° С.

Pros and cons

GOST methods for determining the moisture content of wood are very objective, but they have one big disadvantage- they are cumbersome and slow. The analysis of wood for moisture can take up to 3 days while the samples are dry. In addition, moisture analysis requires cutting a sample from the mass of the test material, which is absolutely unacceptable for determining the moisture content of wood in finished products

Determination of wood moisture with a moisture meter

Method two - indirect (fast and modern)

In order not to bother with the tedious selection and drying of samples, it is much easier and more convenient to "poke" into the wood with a moisture meter. Moisture meter is a special electrical appliance to determine the moisture content of wood. The action of the moisture meter is based on the principle of changing the electrical resistivity of wood depending on its moisture content. The moisture meter has special needles-electrodes that need to be brought into contact with the examined wood and just press the button. The measurement result will immediately be displayed on the screen (or it will be indicated by the deviation of the arrow by the required value, if the instrument has a lever-type scale).

Pros and cons

Determination of wood moisture with a moisture meter is incredibly fast and convenient, refers to non-destructive method control and therefore - ideal for finished products. Alas, electric moisture meters give a large error

Measurement errors in determining the moisture content of wood

The error in measuring the moisture content of wood is

According to the method, no more than 1%
When using electric, within 2 ... 10%

Why is there such a big error when using moisture meters:

Needle electrodes penetrate locally, only to a depth of 5 ... 15 mm. Because of this, a superficial and local study is obtained. wood material... As a result, there is a large percentage of error in comparison with standard GOST methods, where samples are dried throughout the entire volume.

Using the principle of changing the electrical resistivity of wood depending on its moisture content gives an additional error... Because the value of the electrical resistivity of wood depends not only on its moisture content, but also on its density and resin content (for conifers). And since wood is a very changeable value, the probability of an error increases when measuring wood of different tree species in terms of density.
Therefore, each wood species has its own moisture scale... Electric moisture meters are adjusted to the density of one species of wood, usually pine. For other types of wood, manufacturers of moisture meters attach tables or build in calculators for recalculating moisture.
But, even such tricks do not allow to reduce the measurement error less than 2 ... 3%, since the specific electrical resistance of wood directly depends on the density of wood, which can vary greatly even within the same wood species
cm.

Resistivity table of wood depending on the type of wood (visual aid to explain why tables are needed for recalculating moisture depending on the type of wood when using electric moisture meters)

Wood species	Specific electrical resistance (humidity 0%, 20 ° С, ОМ * cm)
	across the fibers	along the grain
Pine	2,3*10 15	1,8*10 15
Spruce	7,6*10 16	3,8*10 16
Ash	3,3*10 16	3,8*10 15
Hornbeam	8,0*10 15	1,3*10 15
Cedar	2,5*10 16	1,9*10 15
Larch	8,6*10 15	3,3*10 15
Approx. These tables were found on the Web, their reliability is unknown. However, even a superficial glance is enough to understand how much the value of the electrical resistivity of wood, which is the basis of the principle of operation of an electric moisture meter, can vary.

Measurement error depending on the type of wood when determining the moisture content of wood moisture meter decreases with the growth of this very humidity and practically disappears at 100%. This is due to the fact that in wood saturated with water electricity goes "directly" through the water, "ignoring" the resistance

Wood moisture measurement units

No matter how the moisture content of the wood was measured, its value is always expressed as a percentage of the total mass. Wood moisture is a quantitative indicator of the percentage of moisture in it. It goes without saying that the moisture content of the wood does not depend on the wood species.

Free and bound moisture in wood

The main part of moisture (water) is contained in wood in intracellular and pericellular cavities and voids, channels, cracks, etc. But, besides this, water molecules are contained in a chemically bound state directly in the thickness.

Depending on the location of moisture in the wood pulp, it (moisture) is divided into two types - and

Free moisture

Free moisture is moisture that is found in the intracellular and intercellular space, as well as in the cavities and voids of wood. Free moisture is also called "capillary". Free moisture is retained in the wood mass due to simple mechanical bonds and is easily removed from it during conventional drying. Free moisture is water that wood can absorb and then release when it dries.

Bound moisture

Bound moisture is a specific term. Bound moisture is moisture that is inside the material of the walls of the cells of the wood, directly in the very

Determine the moisture content of wood

To determine the moisture content of wood, you can use one of two methods. In everyday life, special devices are used - electric moisture meters. The device works on the principle of changing the electrical conductivity of wood (changes with moisture). The needles of an electric moisture meter, with connected wires, are introduced into the tree and an electric current is passed through it, at this moment on the scale of the device you can see the degree of moisture content of the wood in the place where the measurement is taken.

Some experienced carvers can determine the moisture content of the wood by eye. Also, knowing the density and others physical properties different types wood - you can determine its moisture content by weight, in the presence of cracks along the fibers or at the end - by warping. By the color of the wood, the color of the bark and its size, freshly cut or ripe wood is determined, as well as its moisture content.

If, when processing wood with a r / m plane, the chips are easily compressed by hand - the material is wet, but if the shavings crumble and break during compression, the material is dry enough. You also need to pay attention when cross-cutting with chisels: if a piece of wood crumbles, the material is too dry.

A piece of wood that is very easy to cut is very wet, and a wet mark will be noticeable at the cut site. Note that it is quite difficult to obtain a high-quality wood blank, since warping, cracking and other deformations during drying cannot be avoided.

Drying wood

Dry wood is stronger, more durable, finishes better, sticks easily, does not rot, and does not warp so much. Any wood, regardless of the species, he subtly senses the change in the humidity of its environment. This property is one of the most important disadvantages of timber. In warm and heated rooms, it shrinks and dries up, and with high humidity, it very quickly absorbs water and begins to swell. Optimum humidity wood on the street is 18%, and indoors - up to 10%.

Today there are many different methods drying wood. The most accessible and simple is natural look drying - air (atmospheric). Drying should take place in the shade, in a draft and under a canopy. When dried in the sun, the surface quickly heats up and dries up, but the inside of the workpiece remains moist. As a result, cracks appear (due to the difference in stress).

Beams, boards and other p / m must be stacked on wooden, metal or other supports with a height of 50 cm. Boards must be laid with the inner layers towards the top, in order to avoid warping.

If the boards are placed on the edges during drying, the process will be faster, since there will be better ventilation and, accordingly, the moisture will evaporate faster. However, there is a significant drawback - the boards warp more, especially with high humidity... When harvesting live and freshly cut trees, after laying, it is necessary to compact them with a heavy load in order to avoid severe warping.

With natural drying, cracks will always form at the ends. To avoid cracking of the ends, they must be well painted over with oil paint or soaked with bitumen or hot drying oil, this will protect the pores of the wood. End machining must be carried out immediately after cross-section cuts. For very damp wood, it is necessary to dry the ends blowtorch and then start painting over.

Ridges (trunks) must be cleaned of bark (debarked), only at the ends there should be belts-couplings up to 25 cm wide to avoid cracking. Peeling the bark is necessary to speed up drying and protect against bugs. Wood left with bark in a warm room and with a high level of humidity will very quickly begin to rot and be affected by fungi.

After drying by atmospheric method in warm weather, the moisture content of the wood will be between 12 and 18%.

There are other ways to dry wood.

Evaporation method

Evaporation (steaming) has been used since ancient times. The workpieces were sawn into pieces, taking into account the size of the product, then ordinary cast iron was laid and sawdust from the same wood was added, poured with water and left in a heated and cooling furnace at a temperature of 60-70 degrees. As a result of such actions, the process of "leaching" (wood evaporation) takes place - the workpiece loses all its natural juices, becomes colored and takes on thick chocolate shades, with a rather pronounced natural pattern. Such a workpiece is easier to process, and after drying - will be much less warped and cracked.

Waxing method

The wooden workpiece is dipped into a paraffin solution and left in the oven for several hours at a temperature of 40 degrees. Then the wood is allowed to dry out for several days, as a result of which it has the same properties as after curing: a tinted surface with a clear texture pattern, does not warp, does not crack.

Locking method in linseed oil

Cookware made of wood steamed in linseed oil is water-resistant and practically does not crack even during everyday use. This method is still used today. The workpiece is placed in a container, poured linseed oil and steamed over low heat.

Direct - according to the method, indirect - with the help of electrical ones. The first way is accurate, the second way is fast.

Determination of wood moisture according to GOST 17231-78 (GOST 16483.7-71)

Method one - direct (standard, old-fashioned, time-tested)

At the moment, on the territory of Russia there are two standards, both regulating the same method for determining the moisture content of wood:

GOST 17231-78 Chipped and round timber.
Moisture determination methods
Download (Downloads: 1226)
GOST 16483.7-71 Wood.
Moisture determination methods
Download (Downloads: 914)

Analogs of these standards can be easily found in the metrology of any post-Soviet country. Both documents (GOST 17231-78 and GOST 16483.7-71) regulate the procedure for sampling, test and analysis methods for objectively determining the moisture content of timber, timber and firewood (everything from which you can cut or saw off a sample for research). The method for determining moisture content in accordance with GOST 17231-78 and GOST 16483.7-71 is extremely simple and consists in the systematic selection and subsequent drying of samples of the test material. At the same time, the test sample is kept in a drying oven until it is completely dry. After that, weighing and comparison of the weight of the examined wood is made before and after drying.

Pros and cons

GOST methods for determining the moisture content of wood are very objective, but they have one big drawback - they are cumbersome and slow. The analysis of wood for moisture can take up to 3 days while the samples are dry. In addition, moisture analysis requires cutting a sample from the mass of the test material, which is absolutely unacceptable for determining the moisture content of wood in finished products.

Determination of wood moisture with a moisture meter

Method two - indirect (fast and modern)

In order not to bother with the tedious selection and drying of samples, it is much easier and more convenient to "poke" into the wood with a moisture meter. Moisture meter is a special electrical device for determining the moisture content of wood. The action of the moisture meter is based on the principle of changing the electrical resistivity of wood depending on its moisture content. The moisture meter has special needles-electrodes that need to be brought into contact with the examined wood and just press the button. The measurement result will immediately be displayed on the screen (or will be indicated by the deviation of the arrow by the required value, if the instrument has a lever-type scale).

Pros and cons

Determination of wood moisture with a moisture meter is incredibly quick and convenient, belongs to a non-destructive testing method and, therefore, is ideal for finished products. Alas, electric moisture meters give a large error

Measurement errors in determining the moisture content of wood

The error in measuring the moisture content of wood is

According to the method, no more than 1%
When using electric, within 2 ... 10%

Why is there such a big error when using moisture meters:

Needle electrodes penetrate locally, only to a depth of 5 ... 15 mm. Because of this, a superficial and local study of the woody material is obtained. As a result, there is a large percentage of error in comparison with standard GOST methods, where samples are dried throughout the entire volume.

Using the principle of changing the electrical resistivity of wood depending on its moisture content gives an additional error... Because the value of the electrical resistivity of wood depends not only on its moisture content, but also on its density and resin content (for conifers). And since wood is a very changeable quantity, the probability of an error increases when measuring wood of different tree species in terms of density.
Therefore, each wood species has its own moisture scale... Electric moisture meters are adjusted to the density of one species of wood, usually pine. For other types of wood, manufacturers of moisture meters attach tables or build in calculators for recalculating moisture.
But, even such tricks do not allow to reduce the measurement error less than 2 ... 3%, since the specific electrical resistance of wood directly depends on the density of wood, which can vary greatly even within the same wood species
cm.

Resistivity table of wood depending on the type of wood (visual aid to explain why tables are needed for recalculating moisture depending on the type of wood when using electric moisture meters)

Wood species	Specific electrical resistance (humidity 0%, 20 ° С, ОМ * cm)
	across the fibers	along the grain
Pine	2,3*10 15	1,8*10 15
Spruce	7,6*10 16	3,8*10 16
Ash	3,3*10 16	3,8*10 15
Hornbeam	8,0*10 15	1,3*10 15
Cedar	2,5*10 16	1,9*10 15
Larch	8,6*10 15	3,3*10 15
Approx. These tables were found on the Web, their reliability is unknown. However, even a superficial glance is enough to understand how much the value of the electrical resistivity of wood, which is the basis of the principle of operation of an electric moisture meter, can vary.

Measurement error depending on the type of wood when determining the moisture content of wood moisture meter decreases with the growth of this very humidity and practically disappears at 100%. This is due to the fact that in wood saturated with water, the electric current flows "directly" through the water, while "ignoring" the resistance

Wood moisture measurement units

Free and bound moisture in wood

Depending on the location of moisture in the wood pulp, it (moisture) is divided into two types - and

Free moisture

Bound moisture

Bound moisture is a specific term. Bound moisture is moisture that is inside the material of the walls of the cells of the wood, directly in the very

I will give a couple of tips on how to determine yourself whether a board or timber was in drying chamber or not. How to do this without having a moisture meter at hand.

Planed lumber must always be heat treated according to the it is an integral link in the chain of production of planed dry and, both for internal and exterior decoration... This is done specifically to slow down the warping processes in wood, as follows:

Chamber drying, as technological process, is divided into the following stages:

initial moisture heat treatment;
drying wood;
intermediate moisture heat treatment;
final moisture heat treatment;
drying of wood;
conditioning.

What happens to the material if it has not been exposed to the above technological processes in the drying chamber in this article I will not describe because this is a completely different topic, which of course needs to be touched on in subsequent articles.

There are simple and obvious things that immediately catch the eye on a quick inspection. These methods visual definition(whether the material was heat treated in a drying chamber or not) is known to everyone who works or has worked with this material. They are not known only to the layman or the townspeople who are building for the first time on their own!

Of course, in order to determine exactly what percentage of the moisture content of the planed dry material or how well this technological process is performed, you must have a moisture meter on hand. But what if it's not there?

The first thing to pay attention to when inspecting the material:

Price:

All of the above technological processes should be mirrored in the price of the material - less than 12,500 RUB for 1m3 planed-dry material simply cannot exist on retail space in Moscow. Anything below the specified amount is comparable to the game of "Scam", where the loser is always the one who wants to save!

Other sizes:

Planed - dry material has completely different dimensions that differ significantly from the edged material natural moisture GOST 8486 down. This must be taken into account in construction!

For example, the size of the board has a cross-section 140x20x6000mm:

In production planed dry board of this section is used standard size natural moisture cross-section, after processing ( heat treatment in a drying chamber and shaving on a machine) the following calibrated size is obtained cleanly (where a deviation in dimensions in width and thickness of 2-3mm is simply not permissible) -.

In construction, a board of this section is used for the construction of fences, roof lathing and is used in internal finishing works... Where clear (calibrated) dimensions are very important i.e. deviations of 2mm are not allowed, because quite often this board is joined together (see the photo below at the end of the article).

Material that has not been in the drying chamber:

If the material not heat-treated(was not in the cell) and was immediately cautious at the machine, then he has rough, fibrous surface since the blade drags along wet fibers over the entire surface that you can immediately notice with an unarmed eye.(see photo)

The material that has been in the drying chamber has a smooth "mirror" surface.

The photo shows a dry planed board with a cross-section. The fibers reflect light like a mirror, which means the material was in the camera. (see photo)

This is how it looks on site:

Blue on many planed boards:

This is not permissible.

the material has not been heat-treated at all;
the material before heat treatment and clipping on the machine was initially blue ( cut natural moisture GOST 8486) or the blue has gone too deep - a violation of the storage rules;

the material was blue "at the root" i.e. even during preparation round wood;
the material has gotten wet during transportation or subsequent storage.
delivery of planed dry material to the customer and to the sales area to the supplier must be carried out strictly in a closed-type machine;

All this is a marriage that should be sold cheaply at all sorts of sales at a very low price.

Woodworking is one of my hobbies, and when working with natural wood its moisture is important.
In this review, I will talk about a digital device for measuring wood moisture.

For most, this thing is useless, but irreplaceable for the carpenter.
In the off-line, such a device is ... the first and most remarkable kind of 1 in 1: -D in my opinion is not very modest! although I actually saw them in stores for 800-1000 rubles.

A bit of theory.
1. DETERMINATION OF WOOD MOISTURE.

There are several ways to determine the moisture content of wood. To determine humidity, you can use a special device - an electric moisture meter. The operation of the device is based on a change in the electrical conductivity of wood depending on its moisture content. The needles of the electric moisture meter with the electric wires connected to them are introduced into the tree and an electric current is passed through them, while the moisture content of the wood in the place where the needles are inserted is immediately noted on the scale of the device. Electric moisture meters EVA-2M, which determine humidity in the range of 7 - 60%, are widely used.
Many experienced carpenters determine the moisture content of wood by eye. Knowing the types of wood, its density and other physical properties, it is possible to determine the moisture content of wood by mass (weighing several identical blanks of the same species one by one), by the presence of cracks at the end or along the wood grain, by warping and other signs.

When processing lumber with a plane, its thin shavings, compressed by hand, are easily crushed - which means that the material is wet. If the chips break and crumble, this indicates that the material is dry enough. When cross-cutting with sharp chisels, attention is also paid to the shavings. If they crumble or the wood itself is chipped off, this means that the material is too dry.

In practice, wood is distinguished: room-dry (with a moisture content of 8-12%), air-dry artificial drying (12-18%), air-dry wood (18-23%) and moist (humidity exceeds 23%).
Wood from a tree that has just been felled or from for a long time in water, it is called wet, its moisture content is up to 200%. There are also operational moisture content, which corresponds to the equilibrium moisture content of wood in specific conditions.

you can read more about drying sawn timber in

Now about the device ...
it looks like it does in the picture, the set includes a 9V "Krona" battery

Instructions

Performance testing was carried out on a recently purchased edged board 40mm x 200mm x 5 meters. At the time of purchase, the forest was damp, a cursory test showed humidity in the region of 30%.

Moisture measurement of two different boards stacks

Measuring the moisture content of one board in different places at a short distance from each other. as you can see the measurement results at the same level.

Finger skin moisture measurement

According to the measurement results, we can say that the device does not lie, although in some places it showed a humidity of 0%% - |

Summary: I am satisfied with the purchase, for good reason it is necessary to carry out a check with a branded device, but in general the level is wet and this is the main thing.