SPRUCE

Physical and mechanical properties of spruce

In a forest, spruce trees usually grow with a single trunk and a small number of brunches at the bottom and are absolutely straight. In these conditions a part of a trunk that is branchless can reach up to 25m with a total height of a tree amounting up to 60m; the diameter runs between 0.4 and 1.2 m and can reach 2m. On open spaces the tree crown becomes more voluminous while the number of branches increases. Spruce wood is light white or yellow-white in colour with a silk sheen, with no colour difference between sapwood and heartwood. Under the effect of light, spruce wood darkens and becomes yellowish-brown. Tree rings are easily distinguishable, so that the colour of lighter early wood smoothly turns into darker late wood; the edges between growth rings are distinct. Like other softwood, spruce wood has noticeable resin canals and pockets that create a light dotted pattern in cross sections. This is one quality that a fir tree does not possess, and it allows to distinguish the two. Another difference includes the position of branches of a tree trunk: fir branches are usually at a straight angle and leave round marks on a truck, while spruce branches are at a narrow or wide angle and leave oval marks on the tree.

Comparing pine and spruce lumber

Spruce wood is very soft and has an average density of 470 kg/m³ with 12-15% moisture content. With an increase in tree ring width (and a subsequent decline of a late wood percentage), the density decreases and mechanical qualities of wood also worsen. Consequently, only softwood with growth rings between 4 and 6mm (DIN 4074-1) is deemed suitable for construction. The mechanical properties of this wood with such a small density are excellent, that is why spruce wood is extensively used as constructional and building material. Nevertheless, raw spruce is short-lived due to varied weather conditions, while it also rots easily in direct contact with the ground. For exterior purposes, this wood duly needs to be chemically treated. At the same time, spruce possesses comparatively low saturation property; wood moisture content of more than 20% and a subsequent fungal infection hinder absorption. It is relatively easy to process and treat spruce wood by means of sawing, chipping, milling and other techniques. Junction with the help of screws and nails and adhesion also do not cause any difficulties, but trunks with exceeding number of branches, resin pockets and inner tension due to growth conditions can change their shape after usage. Painting, coating and staining do not cause any trouble either.

In house construction spruce wood is widely used for ceiling and overlap beams and pole constructions as it easily supports horizontal load.

Trees that will not rot (information from Johanna Paungger and Thomas Poppe’s book)

These trees should be cut down on the last two days of March when the receding moon is in Pisces. Such days do not occur every year. In past these days were particularly venerated and trees were cut on alternative days: January 1, January 7, January 25, 31 January, February 1 and 2. A tree that was cut on one of these days will not rot and will not be infested with worms.

A tree that was cut on January 1, or from January 31 to February 2 will be with age as firm as a stone.

Only such trees could be used for foundations of wonderful floating buildings in Venice. Had the trees been cut on other, less fortunate days, the splendid city would surely have sunk. Restoring the foundation by means of spruce wood would be a perfect idea, because its durability has been proved by the age of wood, of which the modern piles are made. Any other solution, be it steel, concrete and so on will fail to deliver the same effect. This wood is also suitable for gangboards, planked footways and high buildings on piles.

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