What special features does Robinia wood have as a material?
Abbreviation DIN EN 13556: ROPS
Botanical name: Robinia pseudoacacia, family Fabaceae- Faboideae
Distribution: Eastern North America, cultivated worldwide
Trade names: Robinia, False Acacia, Common Scotchthorn (D), robinia (F), false acacia (GB), black locust, yellow locust (USA), robinia (NL, I), salcam (RO), fehér akác (H)
Originally from North America and traded there under the name Black Locust, the Robinia was first cultivated in Europe as a park and avenue tree. Due to its very good natural durability and high mechanical characteristics, Robinia has also established itself as an important commercial tree species in recent decades. The quality of Robinia wood is largely determined by the trunk shape of the tree, which often has a crooked, eccentric growth, which limits the yield of the assortments. The Robinia wood on the German market currently comes mainly from south-east Europe (Romania and Hungary) and from Brandenburg.
Medium-sized tree of 12 to 25 m (maximum 30 m) in height and 30-60 cm in diameter; knotless lengths usually relatively short, from 2 to 6 m, in closed stands up to 10 m; often crooked, sometimes non-circular and with splayed backs. Planned selection and silvicultural care measures in plantations can positively influence form and dimensions.
Colour and structure
The light, narrow sapwood is clearly separated from the yellow-green to olive-brown core, which darkens to golden brown. The large, highly ethylated early wood pores are arranged in a ring shape and surrounded by light-coloured storage tissue. The late wood pores are also associated with light parenchyma cells and are partly grouped in diagonally running bands. The fibre course is often irregular due to the crooked or eccentric growth form.
Ring-porous, very durable wood with olive to golden brown colour and matt silky sheen.
Frequently irregular grain pattern, caused by curvature and eccentric growth.
Exterior treatment: A treatment with transparent or clear lacquers can be carried out with alkyd or epoxy resin based paints (the latter after priming with DDLack). It is indicated for wooden parts that are not exposed to driving rain or direct sunlight. For protection against strong sunlight, glaze coatings with UV light-absorbing or reflecting pigments have proved to be very effective. We recommend multiple coats with a final thick layer glaze. Top coats or top coats based on alkyd resin or dispersion are possible, but do not allow the attractive grain and colour of robinia wood to show to advantage. Untreated surfaces turn grey when exposed to weathering.
interior treatment: Stains, matting, varnishes or liquid waxes can be used without any problems. Pure DD varnishes are suitable for surfaces subject to heavy wear (e.g. floors), but require a wood moisture content of less than 12%.
Frequent fibre deviations, tensions in the wood and especially the high hardness make the processing of dry wood more difficult and require pre-drilling for nails and screws. Robinia wood is easy to bend, but difficult to split. Carefully processed surfaces (dry, clean, smooth) can be glued together well immediately after planing. The heartwood is difficult to impregnate. Surface treatment is unproblematic with sparingly applied, commercially available agents.
Due to high swelling/shrinkage values and poor permeability (ethylation), Robinia can only be dried slowly and is very prone to boarding. However, good results can be achieved with open air or gentle technical drying and careful conditioning.
Natural durability (DIN-EN 350-2)
Robinia is one of the few cultivated wood species in Europe with durability class 1-2 (according to DIN EN 350). The juvenile heartwood, which comprises the first 7-15 annual rings, reaches, however, according to new scientific research, the highest durability class. According to new scientific findings, it only achieves durability class 4.
Areas of application
Robinia is suitable for outdoor applications with ground contact as well as for decorative applications indoors. Outdoors, the wood is used in gardening and landscaping, in children’s playgrounds and in frame construction (windows, doors, conservatories). Decorative furniture surfaces, stairs and floors can be designed with Robinia indoors. By steaming, the robinia wood can be adapted in colour for indoor use.
The distinctive yellow surface fluorescence of the heartwood is a good distinguishing feature among commercial woods of temperate latitudes. Flavonoid ingredients can cause allergic reactions in sensitive persons during processing. The iron-tannin reaction is pronounced.
Robinia – Technical properties
Weight fresh800-900-950 kg/m³
Bulk density air-dry (12-15% u)0.72-0.79-0.85 g/cm³
Compressive strength u12-1562-73-86 N/mm²
Flexural strength u12-15133-150-167 N/mm²
Modulus of elasticity (bending) u12-1511 600-13 600-17 900 N/mm²
Hardness (JANKA) ⊥, umgerechnet≈ 7,7 kN
Hardness (BRINELL) ⊥ to fiber u12-1531-37-43 N/mm²
Differential shrinkage (radial)0.20-0.26 %
Differential shrinkage (tangential)0.32-0.38 %
Natural durability (DIN-EN 350-2)Class 1-2