Defects, damages, durability

The following defects require greater attention in black locust: uneven annual ring width, eccentric growth, false growth rings, in-grown bark and, last but not least, knots.
Due to its special tissue structure and chemical composition, black locust withstands attacks of biological agents well. The single most important fungus, harming living trees, is Fomes fraxineus Cooke, causing butt rot. Powder post beetle (Lyctus linearis) damage is frequent in the sapwood of stored or built-in wood.
According to our observations, excessive taper (above 1.5 cm/m) occurs in 20-24% of black locust sawlogs.
About 15-20% of the logs processed in the sawmills are bent in one direction. The butt taper in black locust is not very extensive, usually less than 50 cm. Since buttresses and pith-rot are often present, this log part shall preferably be removed.
The sawdust of black locust may cause allergic reactions upon skin contact.
According to the international standard EN 350-2, black locust is the only European species that can be put into the durability class 1-2. Because it does not require chemical treatment for outdoor applications, black locust can be considered a very environment-friendly material.
During a series of focussed investigations, the fungus-resistance of black locust was verified. We selected basidiomycetes fungi that have been also observed in naturally decaying black locust. Steamed and unsteamed black locust heartwood was exposed to such cultures for 12 weeks. Natural wood proved to be completely resistant: the weight loss was 0.1-0.6%. Conversely, steamed black locust has lost some of its resistance in contact with Grifola sulphurea and Irpex lactea (the weight losses were 2.1 and 4.4%, respectively). Accordingly, the steamed, and thus brown-coloured, black locust sawnwood is not recommended for outdoor use or where it is exposed to possible fungal infection.
According to Hungarian and foreign experience, the service life of black locust is estimated to be:

outdoors, in soil contact 25-40 years
outdoors, without soil contact 80-100 years
in dry conditions and under water more than 500 years