Properties of softwood

Spruce or pine? What is the difference and which tree species is best for what? We’ve put together facts about the unique properties of these tree species and potential areas of use.

Spruce or pine – what’s the difference?

Spruce and pine are both common coniferous trees in Sweden. The trees look different and their wood is suitable for slightly different purposes. Older spruce trees often have branches all the way down the stem, while older pine trees are characterised by a long section of stem with no branches. The appearance of the wood is different too. Pine tends to have stronger growth rings and a more reddish colour than spruce. When the timber is planed, spruce tends to have slight tear-out around the knots. Pine is easier to plane without getting this tear-out.

Pine: facts and characteristics

Pine (Pinus sylvestris in Latin) grows across the whole of Sweden. Swedish has several different words for pine. Tallen is the young tree. Furan is the mature tree where the diameter of the heartwood is bigger than half the diameter of the trunk. And then the sawn wood is called furu.

Strength: Medium-hard.

Common uses: Wood interiors and furniture, windows, flooring, veneers, construction timber and boat timber.

Treating pine: Pine goes darker over time. To retain the light colour, pine should be treated with lye. Knots may start to show through a few years after treatment. These should then be specially treated.

Spruce: facts and characteristics

Spruce (Picea abies in Latin) is one of Scandinavia's most common trees. The wood is often softer and lighter than pine. Spruce is found in both sawn wood products and pulpwood.

Strength: Medium hard and elastic.

Common uses: Construction timber, string instruments, flooring, packaging.

Treating spruce: Accumulations of resin are more common in spruce than pine. When dyeing, the impression of the resin can be perceived as stronger because the pigments do not penetrate the wood where there is resin

The strength of wood

Wood is an anisotropic material, which means that the properties differ in different directions. The basic rule is that wood is stronger with the grain, i.e. following the length of the fibres along the stem. Its strength is considerably lower at right angles, i.e. across the grain. This is the case whether the load is caused by compression or stresses in the wood.

The strength is also affected by the density of the wood and its moisture content, its temperature and the period under which it is stressed. Some rules of thumb:

Drier wood is stronger than wood with more moisture.
Colder wood is stronger than warmer wood.
The longer wood is placed under stress, the more its strength reduces.

Wood has good insulation properties

Wood is a material with good thermal properties. This means wood insulates heat well. Thermal conductivity is greatest in the direction of the fibres, and increases with the moisture level and density.

Burning properties of wood

Fire safety is important in all structures. Wooden structures have good fire safety properties, as wood chars slowly. Below the charred surface is normal wood, which retains its original properties. The charring rate is around 0.5–1.0 mm per minute. Larger dimensions and protection of the wood’s surface can enhance a wooden structure’s fire resistance.

The burning properties of wood are affected by several factors. Mainly moisture content, dimensions, density and fibre direction.

Source: Swedish Wood