Laminated-wood construction components can be manufactured with various surface qualities. As there is no standard for the surface qualities of laminated wood, the Studiengemeinschaft Holzleimbau e.V. has defined various qualities in its laminated-wood bulletin.
The desired composition is to be agreed contractually, i.e. stated in the specification.
Surface qualities – laminated wood
| ||Criteria1) ||Industrial quality8) ||Visible quality9) ||Selection quality8) |
|1 ||Firmly grown knots2) 3) ||Permitted ||Permitted ||Permitted |
|2 ||Fallen and loose knots2) 3) ||Permitted ||Up to < 20mm4) permitted |
from > 20mm4) to be replaced in the works
|To be replaced in the works |
|3 ||Resin gall3) 5) ||Permitted ||Resin galls are permitted up to 5mm ||Resin galls are permitted up to 3mm |
|4 ||Knots and faulty points improved by means of knot hole plugs or "ships"3) ||Not necessary ||Permitted ||Permitted |
|5 ||Knots and resin galls improved by means of filler compound3) ||Not necessary ||Permitted6) ||Permitted6) |
|6 ||Insect attack3) ||Permitted are burrows up to 2mm ||Permitted are holes up to 2mm ||Not permitted |
|7 ||Pith ||Permitted ||Permitted ||Pith visibly on the outer lamellas is not permitted |
|8 ||Cracks caused by shrinking3) 5) 7) ||No limit ||Up to 4mm ||Up to 3mm |
|9 ||Discolorations as a result of blue stain, red and brown stripes5) ||No limit ||Up to 10% of the visible surface of the whole construction component ||Not permitted |
|10 ||Mould5) ||Not permitted ||Not permitted ||Not permitted |
|11 ||Contamination of the surface5) ||Permitted ||Not permitted ||Not permitted |
|12 ||Distance between fingerjoints ||No limit ||No limit ||On visible remaining outer lamellas, the distance between one another has to be at least 1m |
|13 ||Surface ||Levelled out ||Planed and chamfered chatter permitted up to a depth of 1mm ||Planed and chamfered chatter permitted up to a depth of 0.5mm |
1)Deviations from the limit values defined in the following in lines 2, 3, 6-9, 12, 13 are to be tolerated to the following extent: maximum of three deviations/m2 visible surface for the quality of vision, maximum of one deviation/m2 visible surface for selection quality.
2)Permissible knot size according to DIN 4074
3)Without limitation of the number
4)Measurement of the diameter of the knots analogue to the measurement of the diameter of individual knots for scantlings according to DIN 4074-1: 2003-06, 220.127.116.11.
6)Filler compound which can be painted over is to be demanded explicitly.
7)The depth of the crack may, independent of the quality of the surface for construction components, be, for members not being subject to tensile-stresses perpendicular to the grain up to 1/6 of the width of the construction component, for members being subject to tensile-stresses perpendicular to the grain, up to 1/8 of the width of the component from each side.
8)According to VOB ATV DIN 18334 to be agreed separately.
9)Corresponds to the requirements according to VOB ATV DIN 18334. If no surface quality is agreed, "Visible Quality" will be delivered
Deviating or further-reaching requirements are to be agreed separately. The edges are normally slightly (3-5 mm) chamfered. Broader chamfers are to be advertised specially. Sharp-edged girder cross-sections are not to be recommended as, in our experience, their edges break out easily when lifted.
Glued laminated timber is, compared with solid wood, mainly a crack-resistant wooden material. Cracks caused by shrinking as a result of fluctuations in the climate are to be put down to the material. They are not a defect and are therefore to be permitted. In the case of colour treatment of the surface, cracks are easier to detect through the high contrast.
Information on the prevention of cracks on the surface can be found in the ”BS-Holz-Merkblatt” (see download area).
Source: Studiengemeinschaft Holzleimbau