Diffuse-porous hardwoods II: poplar, alder, linden and hornbeam

Four very different timbers

This group runs from some of the lightest European hardwoods (poplar) to the heaviest common native timber tree (hornbeam). All have low natural durability. Always check which dataset a figure comes from: the profiles keep European and North American species apart.

Poplar and aspen (Populus)

"Poplar" covers two raw materials: native aspen and black poplar, and plantation hybrids. The wood is soft, light and pale.

Basic density, density at 12-15 % and density at 60 % RH are different measures, so values are not interchangeable. Tension wood and high tangential shrinkage cause distortion and woolly surfaces; the Bavarian report says dry slowly. Do not confuse Populus with the American "yellow poplar", a different tree.

Common alder (Alnus glutinosa)

Alder is a soft, light-to-medium hardwood. Heartwood and sapwood do not differ in colour, and freshly cut end grain turns orange-red and fades as it dries. Identification marks are aggregate rays and brown pith flecks.

• Density 0.55 g/cm3 at 12-15 % MC (range 0.49-0.64), Germany.
• Volumetric shrinkage 13.6 % (Germany), but it is stable once dry and easy to dry.
• Main sawmill risk: staining before drying begins, so convert and dry logs quickly and seal end grain.
• Not durable in weather or ground contact, yet very durable permanently under water (LWG, Germany); no numeric EN 350 class was verified.

Linden / lime (Tilia)

Lime is pale, soft and fine-textured. Small-leaved and large-leaved lime cannot be reliably separated in sawn wood, so treat them as one product.

Shrinkage is fairly high, but the small gap between tangential and radial values keeps dried lime in shape. LWF stresses very high susceptibility to furniture beetle, so stored stock needs attention. No kiln schedule was verified, and American basswood figures must not be copied across: it is a different species.

Hornbeam (Carpinus betulus)

Hornbeam is nearly white, with wavy rings and frequent cross-grain. It is a specialist timber for tool parts, piano actions and flooring.

Worked example 1. Using the same Bavarian leaflet, hornbeam is 0.83 / 0.72 = 1.153 times as dense as beech, about 15 % heavier. It also shrinks more, which LWF calls a drawback and the reason it is unsuitable for construction timber or cabinet timber.

Sources differ by up to about 20 % on strength, so state the source. Dry slowly: LWF warns of warping, checking and staining. No European kiln schedule was found.

Checklist: low-durability hardwoods

• Match the data row to the species: hybrid poplar versus aspen, lime versus basswood.
• Convert alder and aspen logs quickly; seal ends.
• Plan slow drying for hornbeam and keep it out of construction sales.
• Sell all four as interior timber unless the use is permanently under water (alder).

Key points

• Poplar: about 0.45-0.49 g/cm3 (Bavaria), 391-446 kg/m3 for Belgian hybrids; check what you are buying.
• Alder is stable and easy to dry once dry, but stains if logs wait.
• Lime: 0.53 g/cm3, class 5, shrinks but stays in shape; beetle risk.
• Hornbeam: 0.83 g/cm3, about 15 % heavier than beech, shrinks even more, class 5.