What are the special features of oak as a material?

Abbreviation DIN EN 13556: QCXE

Botanical nameQuercus spp.; Family Fagaceae

Dissemination Europe; North America and others

Short description
All woods of the species-rich genus Quercus from the family Fagaceae can be described as oak. Due to the sometimes considerable differences in appearance, structure and technical properties, three assortments are distinguished (white oak, red oak, evergreen oak).

The white oak includes the two common oak (Quercus robur) and sessile oak (Quercus petraea) native to Europe as well as a larger number of species found in North America and East Asia. The red oaks are native to North America. Among the numerous evergreen oaks, mainly found in tropical and subtropical regions of the world, only the cork oak from southwestern Europe is of great economic importance.

Depending on the location, age and species, sapwood is 2-8 cm wide, white to light grey (white oak) or light grey to pale pink (red oak). Heartwood light leather brown, very occasionally also with a reddish tone, in red oaks light reddish grey to reddish brown, rarely also light brown. Annual rings clearly marked by rings of large early wood pores, more or less distinct grain (tangential) or stripes (radial). Wood rays in two different sizes, very narrow and few widths (up to 2 mm) or high (up to several cm), the latter forming very conspicuous mirrors on radial surfaces. White oak and red oak can be distinguished relatively well on the basis of the late wood pore pattern and chemically.

Overall character
Wood clearly structured by ring porosity and large wood rays, whose light to medium brown representatives belong predominantly to the white oaks, the pink-brown ones predominantly to the red oaks.

American white oak may have dark discolorations known as minerals.
Bog oak is a wood which, under certain chemical conditions, turns partially or completely black in wet soils after long-term storage in the absence of oxygen, with only a slight reduction in strength.

Surface treatment
As a rule, oak woods can be stained, matted, glazed and painted by all means without problems. A special feature is the treatment of white oak with ammonia (smoking) to achieve a continuous brown to black-brown colour. However, white oak wood of different origins does not behave uniformly, so that appropriate preliminary tests are necessary.

Medium-heavy woods, red oak with slightly higher strength values; narrowly grown (mild) wood can be worked well with all hand and machine tools; very hard wood with extremely wide annual rings makes working more difficult. White oaks such as red oaks can easily be processed into sliced veneer. Pre-drilling should be done for nails and screws because the wood is easy to split. Gluing is generally good with mildly grown wood, but can be problematic with fast-growing, hard qualities; strongly alkaline glues can lead to staining.

Stability is satisfactory to good in straight grained and mild grades, and impaired in heavy grades by greater swelling and shrinkage. Oak lumber is generally extremely gentle and slow to dry, as the wood tends to crack and warp if dried too hard, and above all to discoloration.

Natural durability (DIN-EN 350-2)
Heartwood of white oak has good resistance to wood-destroying fungi, whereas that of red oak is only moderately durable and unprotected is not suitable for outdoor use.

Areas of application
Due to their similar strength properties, white oak and red oak can be used in the same way in the construction sector (interior finishing) as well as in the furnishing sector (living room, office and kitchen furniture, wall and ceiling coverings, solid wood and finished parquet flooring, wood block paving, stairs). For decorative purposes, the uniformly light-coloured wood of fine-grained white oak is rated highest. White oak is well suited for constructive outdoor applications, red oak less so because of its low fungal resistance. Among the special uses of white oak is the production of liquid containers (tubs, vats, barrels), which are particularly valued in the ageing of high-quality red wines as well as cognac and whisky. Red oak is not suitable for this purpose.
For oak as a whole: Zerreiche (parquet flooring, furniture), evergreen oak (tools), sweet chestnut, berangan (construction wood for medium-duty use (e.g. roofs), interior fittings, furniture parts, panelling, veneer

Contact with ferrous metals causes black-blue discoloration (iron-tanning agent reaction) in wet wood and fasteners can corrode.
Oak – Technical properties
Weight fresh 950-1 100 kg/m³
Bulk density air-dry (12-15% u)0.65-0.76 g/cm³
Compressive strength u12-1542-64 N/mm²
Flexural strength u12-1560-110 N/mm²
Modulus of elasticity (bending) u12-1510 500-14 500 N/mm²
Hardness (JANKA) ⊥, converted5.1-10.7 kN
Hardness (BRINELL) ⊥ to fiber u12-1523-42 N/mm²
Differential shrinkage (radial)0.15-0.22 %
Differential shrinkage (tangential)0.28-0.36 %pH value3.9 (acidic)
Natural durability (DIN-EN 350-2): 2

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