YES - However, fungicidal and insecticidal protection must be applied to ensure the wood is durable enough for use in long-lasting structures. This is because the youngest areas of the wood, known as the sapwood (a pale yellow wood), are susceptible to mould fungi and even rot, depending on their exposure to extreme weather conditions.

The duramen of the pine (a red wood) has its own natural durability, but this part of the tree rarely makes up 100% of a piece of pine timber.

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Depending on how a piece of timber is used - in other words, where and how it is placed within the structure - it is assigned a use class which denotes its risk of attack by wood-destroying fungi and therefore has the required level of durability (either natural durability or increased durability after treatment).

There are 6 use class, each according to the presumed atmospheric and balanced humidity of the wood. PINE may be suitable for any use class.

For a quick summary, here is a decision-support table:

For a more detailed look at the process of assigning a piece of timber to the right use class, see the DTU reference documents (for traditional construction work including cladding and terraces) and the FD P 20-651documentation "Durability of Timber".

Here are a few definitions with extracts from the NF EN 335 and FD P 20-651 standards:

• Use class 1

A situation where the timber is indoors, completely protected from bad weather conditions and not exposed to humidity. Under these circumstances the wood generally has an average balanced humidity of around 6 to 12%.
Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location ⁽¹⁾.
Attacks from discolouring and wood-destroying fungi are minor and always accidental.

• Use class 2

A situation where the wood is indoors or under a shelter, protected from bad weather conditions, with an occasionally higher surrounding humidity with the potential to cause non-persistent humidification (condensation). The wood dries very quickly. Under these circumstances the wood generally has an average balanced humidity of around 12 to 20 %.
Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depends mostly on geographical location ⁽¹⁾.
In this use class, condensation may begin to form around the surface of timber and timber-based products. Attacks by discolouring and wood-destroying fungi may occur.

• Use class 3.1

A situation where the wood is placed outdoors in contact with the ground, and is subject to frequent humidity over short periods of time (several days). The wood becomes completely dry before a new humidity period begins.
The wood is directly exposed to bad weather conditions and the building is designed to quickly evacuate water.

NOTE: certain draining designs that are partly protected from bad weather conditions, with occasional humidity from rain, are assigned use class 2.

Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depends mostly on geographical location ⁽¹⁾.

Attacks by discolouring and wood-destroying fungi may occur.

NOTE: the risk of the wood being affected by fungi depends on the weather conditions and the conditions of use (temperature, relative humidity, driving rain, structural conditions, design details and maintenance provisions).

• Use class 3.2

A situation where the wood is placed outdoors, not in contact with the ground, and is subject to very frequent humidity over long periods of time (several weeks). The wood becomes completely dry before a new humidity period begins.
The wood is directly exposed to bad weather conditions and the building is not designed to quickly evacuate water.
Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location ⁽¹⁾.
Attacks by discolouring and wood-destroying fungi may occur.

NOTE: the risk of the wood being affected by fungi depends on the weather conditions and the conditions of use (temperature, relative humidity, driving rain, structural conditions, design details and maintenance provisions).

• Use class 4

A situation where the wood is:

- either in contact with the ground or a surface subjected to recurring humidity (capillary rise, waterlogged surfaces...) ;
- or in contact with, and partially immersed in, soft water (lake, river, pond) ;
- or exposed to bad weather conditions or other forms of regular humidity, with a design conducive to significant water retention (e.g. horizontal upper surface, non-draining structure...) ;
- or exposed to very significant induced humidity, either due to the overall unique design of the building  (e.g. saturated air humidity causing condensation), or due to an accident (burst pipes).

Attacks from wood-eating insects including termites are possible, but the frequency and scale of these attacks depend mostly on geographical location ⁽¹⁾.

Attacks by discolouring and wood-destroying fungi may occur.

NOTE: timber and timber-based products permanently submerged and saturated in water are not susceptible to fungi attacks, but they are vulnerable to attacks from bacteria.

• Use class 5

A situation where the wood is submerged or partially submerged in salted water (marine environment and natural brackish water).

The main problem is attacks by small marine invertebrates, particularly in hot water, where organisms such as Limnoria spp., Teredo spp. and pholadidae can cause significant damage.

Attacks by wood-destroying fungi, and the development of surface mould and blue stain fungi are also possible.

Sections of certain parts of a structure situated above the water - wood stakes used in ports, for example - may be exposed to wood-eating insects.

GENERAL NOTE: in certain cases, parts of wooden structures may be affected by specific humidity conditions despite being sheltered from direct bad weather. This could require the wood to be reassigned from use class 3.1 to use class 4.

^{(1) If the national standards do not specify the risk of attacks from insects, it is worth consulting local or national experts for advice on the insect attack risks.}

After vacuum autoclave treatment, pine has a durability of 10 to 15 years, even when used in highly exposed conditions (in contact with the ground). Some pine timber structures are now more than 30 years old.

Other preservation processes can also make pine very durable, but only if it is well maintained. Examples include processes that combine preservation with finishing. These processes rely on the quality of the finish to provide a good preservation - and therefore durability - of the wood.

More recently developed processes also exist. These are considered to be innovative but their impact on the durability of French pine is still being assessed. They include most notably the different thermal modification treatments.

This question is not specific enough because it depends on the desired durability.

In fact, it is certainly possible to use non-treated pine in contact with the ground (use class 4), but this will almost definitely be affected by a rot fungus after 1 or 2 years.

The table below shows the correspondence between the main preservation processes and the relevant wood use class, as commonly agreed by the market.

(*) It is important to remember that obtaining pine wood pieces stripped of sapwood is possible in theory, but considered difficult and even impossible for producing common products on an industrial scale.

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YES - However, fungicidal and insecticidal protection must be applied. This is because the youngest areas of the wood, known as the sapwood (a pale yellow wood), are susceptible to mould fungi and even rot, depending on their exposure to extreme weather conditions.

If this protection is applied through brushing, spraying or soaking, it is essential to use a finish to prevent washing of the preservation product by rain. There are several dual-purpose products available which provide both fungicidal protection and finishing.

This finish must of course be maintained to guarantee ongoing protection of the wood. There are also more permanent and long-lasting treatment processes which make finishing unnecessary, including autoclave treatment and thermal modification treatment.

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Autoclaved pine is an interesting solution because it allows for an "unlimited" use of the wood, and safely answers any doubts as to the durability of the word, which can hamper project designs, solutions and implementation processes.

Autoclave impregnated pine cladding (use class 4) can...

• Cover any type of wall, regardless of its direction and gradient, and irrespective of the structure location, climate or immediate environment.
• Have any shape (reminder: impregnation must take place after shaping)
• Be placed using any method (clerestory, overlay, overlapping, interlocking) and in any desired direction (horizontal, vertical, diagonal).
• Withstand termite infested areas

You no longer need to ask yourself "which use class is my cladding?". Less is more. Use class 4 covers all situations where cladding can be used.

It is however important to avoid waterlogged areas as much as possible for facades.

An autoclave is a closed, watertight container in which the content is subjected to several bars of pressure. This 17^th-century invention was used by Nicolas APPERT, a steriliser who invented food preservation.

Autoclaves are also used in medicine to sterilise instruments using superheated steam and in chemistry for certain reactions requiring pressurisation.

In the timber industry, autoclaves are used to impregnate wood by exerting pressure on a liquid. The autoclave can be used for different purposes, including preservation, densification, fireproofing and dyeing.

A Cylindrical autoclave (circular chamber) is called an "autoclave vacuum" and generally uses the BETHELL system or "alternating vacuum and pressure".

A rectangular autoclave (square chamber) is not designed for pressurising the contents and uses the VAC-VAC or "double-vacuum" system. Rectangular autoclaves do not produce as deep an impregnation as the vacuum and pressure system.

Contrary to popular belief, autoclave treatment of wood is done at room temperature. It therefore uses very little energy.

NO - This expression is often used to describe autoclave pressure treatment because the product penetrates deep into the heart of the pine wood. But it is impossible to make the liquid penetrate INTO the very heart of the pine (the duramen) because this is not impregnable.

When a piece of pine wood is cut into sections, therefore, it is normal to find a red (the colour of the duramen), nontreated area.

To keep the treatment protected and ensure the wood remains use class 4, it is essential not to process the timber once it has come out of the autoclave. Any other processing should be carried out before the wood is impregnated.

However, if a cut occurs, the protection will need to be restored using a special "cut treatment" product. The cut timber cannot be used as use class 4.

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"Use class 4" refers to the "use class" of the wood in a structure. The expression "use class 4 pine" is incorrect because a species of wood cannot be assigned a use class; the use class only refers to the location of the timber within the structure.

In general, it is commonly accepted on the market that "use class 4 pine" refers to pine wood that has undergone pressure impregnation in an autoclave using a preservation product that allows it to be used as use class 4.

"Autoclaved pine" is another term used.

This refers to pieces of pine wood that have undergone pressure impregnation in an autoclave.

It is commonly accepted on the market that "autoclaved pine" is the default term for timber that has been impregnated to improve its durability. It is also referred to as preservation treatment. But autoclave impregnation may have other purposes such as fireproofing, densification and dying.

Most products use copper salts as the main active ingredient.

Copper is renowned for being the main element of the famous "Bordeaux mixture" The advantage of copper is its ability to fully attach itself to the cells of the wood, improving its resistance to bad weather conditions.

Furthermore, biodegradable organic compounds help the wood to reach an adequate level of resistance to fungi. These compounds are crop protection products commonly used in agriculture, gardening and industry.

Other preservation products use Bohrium as the main element. But the disadvantage of Bohrium is that it is more easily washable than Copper.

YES - The products used are of course toxic and irritating in their concentrated form, but they are used in a very diluted form in wood treatment.

The CTB B+ quality marking issued by the FCBA attests both to the efficiency and the non-toxicity of the autoclave treated wood in man, animals and the general environment.

NO - However it is almost certainly the most obtainable, widely available and competitive solution.

"Autoclaved pine" will always be more easily obtainable than a hardwood such as oak, chestnut, or an exotic wood such as ipe or padouk, even if it has to go through an impregnation process.

NO - for several reasons - some "green" woods are not treated in a pressure autoclave but instead are dip-dyed in a tank (this is the case for imported products).

Other resinous species - such as fir and spruce - are impregnated with copper salts in an autoclave to improve their durability.

Once treated, these 3 species have the same colour... but not the same durability!

It is not advised to use autoclaved fir/spruce beyond use class 3.1 (timber pieces or vertically positioned timber exposed to bad weather conditions, with no waterlogging risk).

In retail you often see the word "pine" written on autoclaved fir or spruce product labels.

NO - pine and other resinous species can undergo an autoclave treatment adapted for use in use class 3B only.

For example, the Douglas can be pressure impregnated because it also has an impregnable sapwood. However, although the wood takes on a similar colour to that of autoclaved pine, it is not advisable to use Douglas in use class 4 (limited durability). 

NO - Today there are different autoclave treatment solutions for colouring the wood brown or even grey. Ask your supplier.

People like the brown colour because it gives the pine an "exotic wood" appearance, and looks a lot like ipe wood, which is a very popular choice for terraces.

Over time, the colour from the treatment begins to fade and the autoclaved pine gradually turns grey; just like non-treated wood but perhaps a bit slower.

YES - The only way to make certain is to dry the wood.

When the wood is taken out of the autoclave it is drenched in water, so it is important to set time aside for a drying stage before putting it to use. This can be done in the open air or using an artificial dryer.

The NF EN 15228 standard specifies treatment products used to preserve the mechanical properties of wood. The main treatment products are currently available on the market.

LOW - Autoclave impregnation uses very little energy because it only uses electric pumps to fill and vacuum the container, and to pressurise the liquid. The temperature is never raised, which is by definition the most energy-consuming process of all industrial operations.

But all industrial processes have their disadvantages. The disadvantage of autoclave impregnation is that it consumes a lot of water.

Autoclaved French pine has a low grey energy content throughout its life-cycle. This is a locally sourced, low-budget, durable wood, which is used locally and for the most part intended for local markets. Furthermore, this is a process with a 100% yield because each piece of wood that goes through an autoclave can be used, which is not always the case when it comes to other wood upgrading processes.

NO - A product made from autoclave treated pine (treated with copper salts) is considered as nonhazardous industrial waste and does not require any special reprocessing. Use class 4 pine should just be separated from other timber to ensure it is more efficiently recycled.

These treated woods no longer contain heavy metals or arsenic as was once the case. But it is still not advisable to use this type of wood for barbecues or fireplaces.

No, not yet. There are currently two other process types for improving wood durability:

• Heating wood to alter its components (thermal modification)
• Chemical impregnation and grafting to alter the molecules of the wood

Neither of these two process types has yet been proven to work for wood in contact with the ground (use class 4 close) in France.

Certain processes are currently being studied by the FCBA but the results have not yet been published.

Once pine has undergone autoclave impregnation (or soaking in a tank), the same process cannot be used again on the wood with another product. In fact, the two products would get mixed up in the container, causing serious complications, and the efficacy of the initial product would be reduced.

However, there is another process which allows the wood to be impregnated first with a preservation solution, then with a coloured oil to change its appearance. This is called the PROLIN process.

Similarly, saturators can be applied via spraying or brushing to impregnate the surface of autoclaved pine, producing excellent results.

Film-forming (lasure, paint, varnish) is also compatible with autoclaved pine, as long as the wood has been thoroughly dried. For opaque finishes, light colours should be avoided because the copper salts injected into the wood in the autoclave may migrate through the finish, particularly around wood knots, resulting in yellowish stains.

YES - This is what makes the process unique and is the reason why it is so popular among professionals. Any quality of pine wood can be impregnated in an autoclave, and will come out with an improved durability. This process does not produce any downgraded wood unsuitable for use.

It cannot be emphasised enough: it is very rare to find an industrial enhancement process with a 100% yield.

This is a process used to upgrade French pine wood to make it stronger and more resistant to fungi attack.

There are different protocols, but the general principle is the same. The wood is placed in a furnace and subjected to controlled heating (between 140 and 280°C, depending on the process) in a neutral atmosphere that prevents the wood from combusting.

This temperature is maintained for a long period of time (at least 7 hours and occasionally more than 2 days, depending on the process), causing one of the wood's main constituents - hemicelluloses - to disappear almost entirely. It is via the hemicelluloses that the water molecules attach themselves to the wood. By getting rid of them, we allow the wood to become less water retaining, less hydrophilic.

The main outcomes of this treatment include:

• A reduction and even complete elimination of dimensional variations.
• A reduction in fungi development risks.
• A reduction of the mechanical properties of the wood (mainly durability).
• A change in colour: pine that undergoes thermal modification treatment only is dark brown in colour.

The durability of thermally modified pine wood has not yet been properly assessed but it is a solution that has been proven to work for cladding, most notably.

Most of the surface of thermally modified wood quickly takes on a grey then black colour.

NO - For any species, thermal treatment of the wood alters its composition, and the basic statistical data for each species is no longer valid.

For all processes, the bending strength and puncture resistance of the wood are significantly affected and it is generally prohibited to use thermally modified wood for structural purposes. There are no mechanical use class for thermally modified wood.

Autoclave impregnated pine is the most suitable material for use in outdoor structures, bridges, pontoons, walkways, covered courtyards, canopies and shelters. It is also widely used for terraces, decking, cladding and all types of outdoor overlay, both vertical and horizontal.

Pine is also frequently used for outdoor furniture and landscape structures.

Communities tend to put their faith in autoclave treated pine for all outdoor structures because it is a competitive material with a vast range of applications that has proven its worth.

As with all wood, when autoclave impregnated pine is exposed to bad weather conditions and UV rays it starts to grey naturally. This is only the sign of surface deterioration and has no effect on its durability.

This natural phenomenon can only be prevented by using a properly maintained finish. However, be aware that once you have begun this maintenance process it must be constantly repeated.

There are several products available to help give a renewed look to a wood that has turned grey, but it very rarely gets its old colour back.

It is better just to accept that the wood will turn grey.

You will also notice that the colour of impregnated pine changes rather slowly and uniformly.

It is also possible to use "pre-greyed" pine. There are currently two processes for this:

• Old wood grey tinted saturators where the wood can be left to age without the need for maintenance because the natural greying of the wood eventually takes over, completing the finishing process.
• Impregnation in a grey tinted autoclave. The only currently known limit of this process is that it is impossible to use these types of products in contact with the ground (use class 4).

Any type of pine wood - even if it has been treated - requires regular cleaning to maintain a healthy and attractive appearance, particularly when it comes to wood terraces.