What special features does redwood have as a material?
Abbreviation DIN EN 13556: SESM
Botanical name: Sequoia sempervirens, family of Taxodiaceae
Distribution: West Coast of the USA (South Oregon, Northwest California)
Trade names: California Redwood, California redwood, Sequoia, Vavona for grained wood
The Californian redwood is widespread in only a small region of the North American west coast, where it once occurred in large quantities. Due to its proximity to the rapidly developing cities on the Pacific coast, the ease of processing and the versatility of the wood, the stands were heavily overused until the beginning of regulated forestry. The timber now available comes from limited and controlled felling, supplemented by continuous replanting. The coniferous species supplying the Californian redwood is related to the protectedigtree or sequoia of the same region, as is the Chinese primeval sequoia cultivated in Europe.
Unusually large and ageing trees with trunks up to 7 m in diameter and 70 m long. The economically used trunks are knotless up to 25 m and around 1 m thick, straight shafted, round and often slightly deforested (conical).
Color and structure
Sapwood 2 to 4 cm wide, white to yellowish grey, heartwood (dry) first reddish with a slight violet tinge, after longer exposure reddish brown and matt shiny, similar to Western Red Cedar, but mostly darker and of more uniform colouring. Pores (vessels) not present. Wood rays very fine, only still visible on radial surfaces as small mirrors less than 1 mm high. Annual growth rings are clearly visible through a narrow, but sharply defined and dark reddish-brown late wood, appearing on longitudinal sections as pronounced flattening (tangential) or as stripes or lines (radial) (see properties).
Due to the very high age of the tree, the width of the annual rings to the edge of the trunk can be less than 1 mm, resulting in a particularly fine-grained wood with a less clearly protruding structure.
Red-brown, mostly fine and evenly structured coniferous wood.
Occasionally occurring burls of redwood are processed into high-quality veneers and are called Vavona.
Redwood belongs to the light coniferous woods whose strength characteristics, similar to the European coniferous woods, can vary according to the width of the annual ring. The best strength values are achieved with 3-4 annual rings per cm. Redwood can be worked cleanly in any direction with all tools with only little effort; only the coarse-grained qualities tend to have woolly surfaces when milling, drilling and turning. Glueings are of good durability. Ferrous metals and alkalis (e.g. alkaline glues) cause deep brown to black reaction discolorations depending on the degree of moisture. For this reason, clean and dry storage or appropriate packaging is recommended.
In addition to the low weight and ease of processing, a good durability, high resistance to fungal attack, the absence of resin and good thermal insulation of the wood are particularly noteworthy. Redwood is not aromatic.
The technical drying process must be controlled carefully, among other things because of the particularly high initial moisture content. Depending on the moisture content and the thickness of the wood, open-air drying for several months prior to the start of artificial drying has proven to be appropriate.
Exterior use: Pigmented impregnation glazes are, according to the current state of the art, particularly economical, easy to use and have proven to be particularly durable.
Interior use: For this application area, colourless glazes and matting are preferred. If special protection of the surface is required, transparent varnishes can also be used with good success. For special effects in interior decoration, high gloss polished surfaces can also be achieved. With both methods, the wood moisture content must not exceed 12%. Untreated and weathered wood tends to leach out at first, later the surface starts to grey; however, experience shows that redwood is best used untreated from coniferous woods.
Areas of application
Redwood is mainly used in surface-forming forms where, in addition to low weight, an attractive natural colouring and structure are important. Here it can be used in interior finishing for acoustic, wall and ceiling cladding, room dividers, mouldings and framing, and because of its good weather resistance, it can also be used in exterior construction for facades, wall, balcony and garage door cladding, wind springs, roof underlays, headboards, shutters, pergolas and in damp rooms such as swimming pools or bathrooms. Because of its good stability, redwood is also suitable for light frame constructions as well as for stud and built-in furniture. A special use is in the production of soundboards and organ pipes. Due to the low compressive strength of redwood, applications with corresponding stresses should be avoided.
In England and partly also in the international timber trade the term redwood is also used for European pine woods, e.g. Baltic redwood
Redwood – Technical properties
Weight fresh850 kg/m³
Weight dry-dry380 kg/m³
Compressive strength u12-1537 N/mm²
Flexural strength u12-1558 N/mm²