1. LVL AS A CONSTRUCTION MATERIAL Figure 1.65: Appearance of LVL veneer surfaces 1. Unsanded front side, close image 2. Optical sanded front side, close image 3. Unsanded reverse side with dark scarf-joint glue line, close image 4. Optical sanded reverse side with dark scarf-joint glue line, close image 5. Unsanded front side, general view 6. Optical sanded front side, general view 7. Calibration sanding revealing the dark glue line 11. 1 5 2 6 3 7 4 Metsä Wood resist seismic loads. LVL-C members, in particular, are not sensitive to cracking or brittle failures of connections, so they can yield and absorb more energy. Full utilization of these properties and use of LVL in higher dissipative classes for structures in seismic design requires testing in cyclic loading according to EN 12512 for combinations of LVL panels and dowel type connections. 1.12.7 Visual properties of LVL surface Softwood LVL is produced from peeled conifer softwood veneers. An inherent characteristic of conifer wood is that branches are located in star-like clusters along the stem (knot ringlets) and therefore there may be frequent knots in a peeled veneer. LVL is mainly used as a structural load-bearing product for non-visible applications. Therefore, the sorting of veneers in production is based mainly on the strength properties of the veneers, not on their visual properties. During peeling, small peeling cracks are formed in the veneer. These cracks may become visible due to swelling or shrinkage caused by moisture variations or sanding. In addition, the scarf-joints of face veneers can sometimes overlap, leaving the joint slightly open. Due to moisture variations this may also occur later on the surface of sanded products. Other possible surface defects include resin pockets, bark, and splits. Unsanded surfaces may have some stains of adhesive from the production process. Some manufacturers provide higher grade face veneers on special request. On the front side of the product a light-coloured melamine adhesive is used for scarf-jointing the surface veneers. On the reverse side the scarf-joints are glued with the same dark brown phenol resin adhesive used in the glue lines between veneers. The distance between scarf-joints is usually 1.9 m or 2.5 m depending on the production process. When LVL members are used in visible applications, the designer specifies which side of the member is the visible surface. This must also be taken into consideration especially when the LVL is to be cut into special shapes. Standard LVL is delivered unsanded. It can, however, be sanded to improve the visual appearance of the LVL surface by so-called optical sanding which cleans and smoothens the surface by removing any dark glue stains and equalizing any local colour differences of the veneers. Another alternative sanding treatment is calibration sanding, which can be carried out to achieve more precise thickness tolerances for, e.g., LVL door components. Unless some non-transparent coating is used on the surfaces, the calibrated sanding is not recommended for visible applications, because it can sand through the surface veneers revealing the dark glue line especially in the thicker range of the products 11. For more information on sanding specifications, see subsection 1.7.1. LVL Handbook Europe 47
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