LARCH

Physical and mechanical properties of larch

Larch belongs to a group heartwood trees. It has a core of reddish-brown colour and an abruptly limited, narrow white and slightly yellow sapwood, very distinct growth rings with a sharp border between early and late wood.

The texture of larch is determined in longitudinal section by the width of tree rings, differences in colouring between early and late wood as well as heartwood and sapwood. The texture is especially rich and beautiful in tangential section. Larch wood does not have branches or branch stubs.

The colour of wood (core) is characterised by this set of parameters:

  • colour hue, nanometre — 583.5;
  • clarity, % — 54.0;
  • lightness, % — 32.5.

Macrostructure statistics

Resin canals are small and scarce. An average number of growth rings in 1 cm of cross section significantly varies depending on the area of tree’s origin.

Larch wood exhibits relatively low overall density as it varies greatly in early and late wood.

Physical properties

Moisture content and connected qualities.

Freshly cut wood exhibits a moisture content of 82%. The maximum moisture content during water absorption is 126%. Like with other types of trees, a growing larch tree shows seasonal and daily fluctuations of moisture content, which occur to a substantially smaller degree while maintaining the general pattern.

Moisture absorption and water uptake of a larch tree are significantly lower than those of a pine tree due to higher density. If the protective coating is used, objects made of larch wood retain virtually the same level of moisture content, which makes larch perfect for parquet floors. Hydraulic conductivity is also substantially lower in larch than pine, spruce or birch trees, which requires a special approach in the drying process of saw-timber.

Larch wood is a type of wood known for strong shrinkage. Tangential shrinkage of an early zone of a growth ring amounts to 7.8%, for late zone — 9.4%. Average value of a wood swelling factor:

  • radial — 0.2;
  • tangential — 0.38;
  • volumetric — 0.60.

An important characteristic of wood is its swelling pressure. For a larch tree (core) under normal conditions, it amounts to:

  • radial — 0.91 MPa.

Much higher in comparison to pine and spruce trees are also inner tensions, which occur during the drying process of larch timber. That is why such sawtimber is prone to crack and corrode more than other softwood while drying.

Density

The average value of larch wood density with a normal moisture content (12%) is 665 kg/m³, absolutely dry wood — 635 kg/m³, average base density — 540 kg/m³.

Density of larch wood depends largely on the type and place of upgrowth.The highest density has been found in larch timber from the Altai region (12=725kg/m³), followed by larch logs from the Urals and near Urals region. European larch possesses the lowest density (12=506 kg/m³).

Permeability to gases and liquids

Air permeability of larch wood (core) is the lowest of all our wood types. The same can be said about water permeability. As a result of this, larch wood is hard to treat with protective substances.

Mechanical properties

In addition to beautiful texture and colour, larch exhibits a high durability index. It is insignificantly surpassed by hardwood trees. Its mechanical properties also significantly depends on the type and place of upgrowth, therefore we shall provide averaged data.

Breaking point

  • static bending — 108 MPa;
  • stretching along the grain — 124 MPa;
  • compression along the grain — 61.5 MPa;
  • shearing along the radial plane — 9.78 MPa;
  • shearing along the tangential plane — 9.11 MPa;
  • elasticity coefficient during stating bending — 14.3 GPa.

Technical and functional properties

impact elasticity — 53.1 kJ/m²;

hardness:

  • face plate — 42 N/mm²;
  • radial — 31.5 N/mm²;
  • tangential — 33.4 N/mm²;

microhardness:

  • early wood — 20.1 MPa;
  • late wood — 134.2 MPa;

impact resistance — 0.9 kJ/cm²;

wear resistance:

  • lateral — 0.07 mm;
  • radial — 0.17 mm;
  • tangential — 0.14 mm.

It is about 80% lower in comparison to pinewood.

During the prolonged endurance of deformation larch wood shows better results than pinewood (15-20%).

Ability of larch/pine wood to maintain fastenings:

  • radial direction — nails 236.8/124.9 N/mm, screws 129.9/93 N/mm;
  • tangential — nails 231/123 N/mm, screws 141/88 N/mm;
  • face plate — nails 121.2/61.5 N/mm, screws 85/55 N/mm.

Bending capability, characterised by the ratio of cross-sectional height h (thickness of a rough production) to the bend radius R is h/R=1:14 (for beechwood −1:2.5; for pinewood 1:11).

Possessing high physico-mechanical properties, larchwood nevertheless requires a specific technological approach in production and treatment. Saw blades get rather oily during sawing. It is difficult to work on larchwood with regular tools, but at the same time it is easily polished and painted on after deresination.

Larchwood that has been procured and prepared in the Altai region, near the Baikal, in the upper course of the Lena and Angara rivers, possesses the best properties.

Larchwood belongs to the group of woods that are resistant to fungal infections and other biological effects. This biological resistance only strengthens in the course of tree or wood’s life; more bio-resistant wood is in the bottom part of a tree trunk. This parameter is estimated in comparison to basswood (with a set value of 1). The core of a larch tree shows the highest estimate among Russian woods — 9.1, followed by oakwood — 5.2.

The continuous influence of water increases hardness of larchwood. During the construction of the city of Venice more than 400 000 larchwood piles were used to strengthen the foundations of various buildings. In 1827, 1000-1400 years later, some of the piles were examined, drawing outstanding conclusions: larchwood piles that stood underwater and supported the city had virtually turned to stone, so hard they were. Wood has become so firm that an axe or a saw can barely affect it.

Tree that does not shrink (information from Johanna Paungger and Thomas Poppe’s book)

When wood is used, in many cases it is vital that the wood does not shrink and its volume and size stay the same. To procure such wood, it is best to fell trees on December 21 between 11am and 12pm. It is the best day for tree felling. Beside this day, it is possible to cut down trees in winter during an early receding moon.

Alternatively, the best times for cutting trees that are not affected by shrinkage are February evenings after sunset during the receding moon, September 27, monthly three days after the new moon. A tree cut during a new moon in Libra is also resistant to shrinking and can be used for manufacturing and construction. As it ages, a tree cut after the sunset in February will become as firm as a stone.

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