Specimens of beech, ash, lime and poplar were thermally modified (T) and treated with an aqueous solution of melamine (M) resin to investigate the mechanical changes after combined (double) modification (TM). Density, solution uptake, weight percent gain, bulking and equilibrium moisture content were recorded to ensure proper treatment. Samples for Brinell hardness and three-point bending were cured at 120°C under dry conditions. The WPGs of the two treatment groups M and TM were similar, but bulking of TM specimens was negative. This might indicate an incomplete penetration into the thermally modified cell wall in combination with a potential leaching of soluble hemicellulose components by the alkaline impregnation solution. The decreased hardness of heat-treated wood was substantially increased by melamine treatment (combined modification). Both modifications and their combination slightly increased the modulus of elasticity. The modulus of rupture was increased after melamine treatment, decreased after thermal modification and combined modification. The work in bending was severely reduced for all treatments. Melamine treatment of thermally modified wood was carried out successfully and some mechanical properties were improved. Double-modified wood with increased modulus of rupture (MOR) and extraordinary surface hardness would be suitable for non-structural outdoor applications such as decking and cladding. Abbreviations: ANOVA: Analysis of variance; EMC: Equilibrium moisture content; EMC_R: Reduced (corrected) equilibrium moisture content; IB: Impact bending strength; M: Melamine treated; MOE: Modulus of elasticity; MOR: Modulus of rupture; MUF: melamine-urea-formaldehyde resin; OD: Oven dry density; R: Untreated references; RH: relative humidity; SC: Solid content; SU: Solution uptake; T: Thermally modified; TM: Thermally modified and melamine treated (double modification); WB: Work in bending; WPG: Weight percent gain

Background and Objectives: In the near future, in Europe a raised availability of hardwoods is expected. One possible sales market is the building sector, where medium dense European hardwoods could be used as load bearing elements. For the hardwood species beech, oak, and sweet chestnut technical building approvals already allow the production of hardwood glulam. For the species maple and ash this is not possible yet. This paper aims to evaluate the economic feasibility of glulam production from low dimension ash and maple timber from thinnings. Therefore, round wood qualities and the resulting lumber qualities are assessed and final as well as intermediate yields are calculated. Materials and Methods: 81 maple logs and 79 ash logs cut from trees from thinning operations in mixed (beech) forest stands were visually graded, cant sawn, and turned into strength-graded glulam lamellas. The volume yield of each production step was calculated. Results: The highest volume yield losses occur during milling of round wood (around 50%) and “presorting and planning” the dried lumber (56%–60%). Strength grading is another key process in the production process. When grading according to DIN 4074-5 (2008), another 40%–50% volume loss is reported, while combined visual and machine grading only produces 7%–15% rejects. Conclusions: Yield raise potentials were identified especially in the production steps milling, presorting and planning and strength grading.

In this study, a specimen geometry for testing finger joints was developed using finite element simulation and proofed by experimental testing. Six different wood species and three adhesives were used for finger-jointing specimens. With the test specimen geometry, the bonding strength of the finger joints was determined without the usual self-locking of the joint. Under load, the test specimen geometry introduces maximum stress at the beginning of the bond line (adhesive zone). However, the test specimen geometry does not generate a symmetric stress state. The main difficulty here is the flank angle of the finger joint geometry. The wood species and adhesives significantly influenced the performance of the finger joints.

The biological durability of wood is an important property for outdoor applications of wood-based products. In temperate climate zones, the most critical biological hazard is wood-destroying fungi, and the European standard EN 350 in combination with EN 113-2 provide guidance on sampling, testing, and classifying wood durability against brown and white rot fungi. However, in their latest revised versions, both standards recommend the use of probability density functions for fitting mass loss data (ML). Subsequently, the durability of wood and its variability should be further characterised. The aim of this study was to statistically analyse the ML data from laboratory agar plate tests with different European-grown wood species and to examine the effect of different statistical treatments on the standardised classification scheme of wood durability. It was concluded that more precise guidance is needed on the sampling procedure since significant differences in durability exist between stem zones. The assignment of dispersion indicators requires a revision to ensure clear, unmistakable, and reproducible durability classification of wood. Deficits in the description of the proposed statistical treatments in both standards became evident. It can be questioned whether the application of probability density functions provides additional information about the variability of wood durability.

Recently, certain European standards have allowed for the classification of the biological durability of chemically modified wood and preservative-treated wood, including treated products, but necessary methods for representative sampling and testing are lacking. Instead of sampling from products that can contain areas of varying durability, this study aimed at testing full-size products. Sections of untreated and preservative-treated terrace decking and palisades were incubated with pure cultures of brown and white rot fungi. Instead of mass loss, the decayed cross-sectional area was determined. The spatial distribution of decay and wood moisture content was investigated. After 16 weeks of incubation, all untreated product specimens showed signs of decay independent of the test fungus. The treated specimens were less affected. The mean and the maximum decayed cross-sectional areas were well correlated, for both the total and the sapwood cross-sections. The wood moisture content after incubation was always favorable for fungal decay, but highest where the specimens were in direct contact with the malt agar. Different infestation pathways became evident: (1) from the sapwood mantle, (2) via radial checks, and (3) from the end-grain. The latter should be prevented in order to better mimic real outdoor exposure conditions.

Sapling-wood products from different wood species such as willow (Salix spp. L.) and Common hazel (Corylus avellana L.) are frequently used for gardening and outdoor decoration purposes. Remaining bark is suggested to provide additional biological durability. Even for temporary outdoor use it seemed questionable that durability of juvenile sapwood can provide acceptably long service lives of horticultural products. Therefore, sapling-wood from seven European-grown wood species was submitted to laboratory and field durability tests. In field tests, specimens with and without bark were tested in comparison and submitted to differently severe exposure situations, i.e., in-ground contact, and above-ground situations with and without water trapping. All materials under test were classified ‘not durable’ independently from any potential protective effect of remaining bark, which contradicted their suitability for outdoor applications if multi-annual use is desired.