What are the special features of ash as a material?

Abbreviation DIN EN 13556: FXEX

Botanical name Fraxinus excelsior; Fraxinus spp.; family of the Oleaceae

Dissemination Europe, Middle East, North America

Trade names: frêne (FR), frassino (IT), fresno (ES), ash (EN)

Short description
The commercial assortment of ash comprises numerous species, which are mainly native to North America and Europe. Like beech, ash is a so-called facultative heartwood former, i.e. the colour core can only be formed later (at the earliest at the age of 40) induced by exogenous factors (e.g. injuries). According to the current developments on the market for furnishing woods, ash is one of the most important hardwood suppliers. Especially the light colour and the ring-porous structure characterise the decorative wood image. But also the seldom occurring olive core of the ash currently achieves a high added value. The frequently occurring brown heartwood core of ash usually leads to a reduction in the value of the trunks. In the course of the revaluation of vividly coloured woods (cf. red-heart beech), however, a trend reversal is also becoming apparent here.

The sapwood of ash is white to yellowish and very wide (up to 19 cm). The heartwood retains the light yellow colour of the sapwood. With age an optional colour core can be formed. In American ash this core is usually grey-brown to brown, in European ash grey-brown to olive and often cloudy (so-called brown heartwood). In individual cases, a striped olive-brown colour core can be formed, comparable to olive wood (Olea europaea). The growth zone boundaries are clearly visible through the multi-row, large early wood pores. These form prominent stripes (radial) and flakes (tangential) on the longitudinal surfaces. There is no interlocked twist and rarely latch growth.

Overall character
Ring-porous, very rich in structure, decorative, hard and very elastic wood with colour variability from whitish over olive to brown.

The hard and elastic wood is easy and clean to work. It is easy to bend, knife, peel, turn and glue. Pre-drilling should be done for nails and screws. The surface treatment is unproblematic, pore fillers can be used to lighten the wood optically, e.g. by so-called lime. UV protective varnish is advisable to prevent yellowing.

With gentle drying, cracks and warping can be largely ruled out.

Natural durability (DIN-EN 350-2)
The natural durability of ash, including the colour core, is poor according to the classification in durability class 5 of DIN EN 350, as the core materials are not embedded in the cell walls.

Areas of application
Due to its low natural durability, the wood is mainly used for interior applications. Here it is particularly suitable for decorative veneers, floors, stairs and furniture. Ash wood is also used for dynamically stressed parts such as sports equipment, tool handles, ladders, boat straps and musical instruments (batons). Through thermal modification, the natural durability and dimensional stability of ash wood can be significantly improved, making it suitable for outdoor use.

Metals cause dark discoloration when combined with moisture.

Ash – Technical properties
Weight fresh 600-800-1 140 kg/m³
Bulk density air-dry (12-15% u)0.45-0.69-0.86 g/cm³
Compressive strength u12-1520-44-68 N/mm²
Flexural strength u12-1549-102-178 N/mm²
Modulus of elasticity (bending) u12-154 400-13 400-18 100 N/mm²
Hardness (JANKA) ⊥, converted6.7-10.5 kN
Hardness (BRINELL) ⊥ to fiber u12-1528-40 N/mm²
Differential shrinkage (radial)0.17-0.21 %
Differential shrinkage (tangential)0.27-0.38 %pH-Wert≈ 5.8
Natural durability (DIN-EN 350-2)5

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The U-value window is calculated using the formula W/(m²K), i.e. watts per square metre and Kelvin. This value refers to the entire window and defines the amount of energy per unit of time that flows through an area of one square meter when the air temperature on both sides differs by one Kelvin. The lower this value is, the less energy or heat the window emits.

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