Ring-porous hardwoods I: oak, ash and elm

What "ring-porous" means

In ring-porous woods the earlywood pores are clearly larger than the latewood pores and form a visible ring on the end grain. Oak, ash and elm are the classic European examples, and robinia and sweet chestnut (next lesson) share the pattern. Their rough-sawn faces look alike.

Oak (Quercus robur and Q. petraea)

Pedunculate (robur) and sessile (petraea) oak are treated as one commercial product; separating them in sawn wood is not practical. Heartwood is light to medium brown, the wood has 2-4 rows of large earlywood pores and rays visible on all three surfaces.

LWF Bayern also cites field trials giving class 5 in the ground and class 4 above ground, so "durable" is optimistic. Exclude or protect sapwood outdoors.

• Sawing: quality is set by the log. Shake and heart defects only show when the board is cut, so inspect log ends.
• Iron and tannin: wet oak reacts with iron to give blue-grey to black stains. Avoid steel contact on wet boards.
• Drying: extremely gentle and slow, with checks, collapse and discolouration as risks. A Romanian review quotes up to 35 days for 25 mm lumber in a conventional kiln (probably North American data); its optimised schedule holds 30-40 C until 27 % MC, then rises to 60 C.

European ash (Fraxinus excelsior)

Ash is ring-porous like oak but has latewood vessels almost invisible to the naked eye and rays visible only on the radial surface (Timber Atlas). A brown or olive heart can form in old trees; it does not reduce strength but is often rejected for fitting-out wood.

The two datasets disagree most on tangential shrinkage (8.0 against 9.6 %), so quote a range in contracts. Ash is hard and tough for its density. The Merkblatt says it dries without problems; saw promptly, preferably before summer, through-and-through to avoid side cracks. Impregnation is hardly possible, so it is an interior timber. Ash dieback brings rot and stain in butt logs.

Elm (Ulmus)

All native elms are sold together in the trade, because species cannot be reliably separated in sawn wood. Elm has obligatory heartwood with large earlywood pores in 1-3 rows and latewood vessels in wavy light bands on the end grain, plus a distinct jagged figure on tangential faces.

• Density 0.65 g/cm3 mean air-dry (0.48-0.86), Germany (LWF, elm in general); wych elm 605 kg/m3 (Wood Database).
• Shrinkage conflict: LWF gives tangential 6.9-8.3 %, the Wood Database 12.4 % for wych elm; stability is uncertain.
• Heartwood class 4 (EN 350-2, stated for European white elm): interior use.
• Interlocked grain makes planing difficult. No drying schedule could be read: dry gently and trial it.
• Dutch elm disease has cut supply. Keep American elm data separate from European elm.

Checklist: oak, ash or elm?

• Rays visible on end grain and tangential face: oak.
• Latewood vessels nearly invisible: ash.
• Wavy light latewood bands and jagged tangential figure: elm.
• Colour alone is a weak cue.

Key points

• Oak: about 0.71 g/cm3 (Germany), shake and iron stain are the main handling issues; dry slowly.
• Heartwood "durable" for oak rests on an older class and field trials give lower results; exclude sapwood outdoors.
• Ash: oak-like density (0.69) but class 5; no large rays.
• Elm: one commercial product, class 4, conflicting shrinkage data; supply hit by disease.