Weathering of Radial and Tangential Wood Surfaces of Pine and Spruce

Abstract

SummaryThe development of cracks and changes in appearance have been investigated on radial and tangential surfaces of pine (Pinus silvestris L) and spruce (Picea abies Karst) which have been exposed outdoors for 33 months. The degradation of the surfaces has also been studied at the micro-level. Untreated samples, samples impregnated with a CCA-agent and samples surface treated with linseed oil have been tested. The annual ring orientation is the most important factor for crack development on weathering. The type of wood, impregnation treatment and surface treatment with linseed oil have only a marginal effect on the crack development. No relation has been found between the density of the samples and the crack development. After 33 months of outdoor exposure, tangential surfaces of pine have 13 times more total crack length per unit area than the corresponding radial surfaces. In spruce, the total crack length on the tangential surfaces is 6 times greater than on the radial surfaces. Tangential surfaces of both pine and spruce have a greater number of cracks per unit area and wider cracks than the corresponding radial surfaces. Tangential and radial surfaces show the same colour change in the surface as a result of weathering. On the micro-level, tangential surfaces have more and deeper cracks than radial surfaces. The cracks on the tangential surfaces occur frequently in both earlywood and latewood. On radial surfaces, cracks occur primarily at the annual ring borders, but to a certain extent also in the earlywood. The radial cell wall of the earlywood has a large number of pits which are degraded at an early stage. Decomposition of the cell wall takes place on both radial and tangential surfaces. Cracks arise which follow the S2 fibril orientation in the cell-wall. Delamination in the middle lamella is especially noticeable in the latewood on tangential surfaces. No differences have been observed regarding linseed oil treatment, impregnation or type of wood.

Thermo-hydro and thermo-hydro-mechanical wood processing: An opportunity for future environmentally friendly wood products

“…Laser treatment, depending on irradiation parameters, is a form of heat treatment which is very concentrated in space and time and exhibits interesting effects such as a molten surface. This type of molten surface was observed by Sandberg (1999) and Johansson and Sandberg (2007) during preparation of weathered samples of pine and spruce with the help of UV-laser ablation (Seltman 1995a,b). Haller et al (2001) have investigated the effect of laser irradiation on wood with respect to changes in structural, chemical and physical properties, and they have identified the laser parameters which guarantee melting of wood without pyrolysis.…”

“…In contrast, Jämsä et al (2000) found that heat-treated pine and spruce surfaces cracked to the same extent as unmodified wood when exposed outdoors. However, Sandberg (1999) and Sandberg and Sö derströ m (2006) have shown that the tendency of wood to crack during weathering is strongly related to the annual ring orientation in the cross section of the wood. To avoid cracks occurring on wood used outdoors, wood should be selected with the annual ring orientation perpendicular to the exposed wood surface.…”

Radially sawn timber?the Primwood Method for improved properties

“…Within the R&D-program Value Activation, an idea was developed to saw timber with rectangular and triangular cross-sections in a pattern which gives a high volume yield (Sandberg 1998). This method, which gives timber with vertical annual rings, is called star-sawing, Figure 1. A number of investigations have been made on the sawing technique (Sandberg 1996a(Sandberg , 1997a(Sandberg , 1998, on the utilization in particular of the timber with a triangular cross section (Sandberg et al 1996, and on properties which are important for the use of the material in different products (Holmberg 2000, Sandberg 1996b, 1997b, 1997c, 1999, 2003. On the basis of this knowledge, a new industrial manufacturing system, the PrimWood Method, has been developed.…”

Structural Evaluation of a Timber Construction Element Originating from the Great Metéoron Monastery in Greece

“…Macroscopic view of the transversal surface of the old wood sample: Wood surface in silver gray (1) and darkish gray (2) color, asymmetrical wood structure (3), splits (4) and checks (5) in the wood structure, and slightly eroded wood fibers in the surface of the wood element (6) All of the changes that appeared in the wood surfaces could be considered the outcome of weathering. The weathering of wood is the result of the actions of cyclic wetting and drying, exposure to ultraviolet (UV) light, and erosion of the wood surface through the wind load (Feist 1990;Sandberg 1999;Anthony 2007;Lebow and Anthony 2012).…”

“…These turned into longer splits due to cyclic wetting and drying of wood or freeze-thaw action. The weathering process changed the general appearance of wood and gradually eroded the wood fibers (Feist 1990;Sandberg 1999;Anthony 2007;Lebow and Anthony 2012).…”