Rock Elm (Ulmus thomasii)
Rock Elm (Ulmus thomasii)

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Common Name(s): Rock Elm, Cork Elm

Scientific Name: Ulmus thomasii

Distribution: Midwestern United States

Tree Size: 65-100 ft (20-30 m) tall, 2-4 ft (.6-1.2 m) trunk diameter

Average Dried Weight: 47 lbs/ft3 (755 kg/m3)

Specific Gravity (Basic, 12% MC): .57, .75

Janka Hardness: 1,320 lbf (5,870 N)

Modulus of Rupture: 14,800 lbf/in2 (102.1 MPa)

Elastic Modulus: 1,540,000 lbf/in2 (10.62 GPa)

Crushing Strength: 7,050 lbf/in2 (48.6 MPa)

Shrinkage: Radial: 4.8%, Tangential: 8.1%, Volumetric: 14.9%, T/R Ratio: 1.7

Color/Appearance: Heartwood is light to medium reddish brown. Paler sapwood is usually well defined.

Grain/Texture: Grain is interlocked (making it very resistant to splitting). With a somewhat coarse, uneven texture.

Rot Resistance: Rated as non-durable; susceptible to insect attack. Living trees are susceptible to Dutch elm disease.

Workability: Can be a challenge to work because of interlocked grain, especially on quartersawn surfaces. Planing can cause tearout and/or fuzzy surfaces. Poor dimensional stability. Glues, stains, and finishes well. Responds well to steam bending, and holds nails and screws well.

Odor: Elm usually has a strong, unpleasant smell when green; though once dried has very little odor.

Allergies/Toxicity: Although severe reactions are quite uncommon, Elm in the Ulmus genus has been reported as a sensitizer. Usually most common reactions simply include eye and skin irritation. See the articles Wood Allergies and Toxicity and Wood Dust Safety for more information.

Pricing/Availability: Should be moderately priced, though availability from mature trees has been greatly diminished by Dutch elm disease.

Sustainability: This wood species is not listed in the CITES Appendices or on the IUCN Red List of Threatened Species.

Common Uses: Boxes, baskets, furniture, hockey sticks, veneer, wood pulp, and papermaking.

Comments: Elm trees are commonly infected with Dutch elm disease, a fungal disease spread by elm bark beetles. D.E.D. has wiped out millions of Elm trees worldwide.

Related Species:

Related Articles:

Scans/Pictures:

Rock Elm (Ulmus thomasii)
Rock Elm (sanded)

Rock Elm (sealed)
Rock Elm (sealed)

Rock Elm (endgrain)
Rock Elm (endgrain)

Rock Elm (endgrain 10x)
Rock Elm (endgrain 10x)

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Randy Hauck
Randy Hauck

I have found specimens of some tree standing but dead, even free of bark, long dead, but completely free on rot, even when found on the ground. Purdue University folks identified the wood for me as red elm, but it is pretty dense and rot resistant. Would that likely be rock elm?