Surface repair

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)
Firmly grown knots2) 3) Permitted Permitted Permitted
Fallen and loose knots2) 3) Permitted Up to < 20mm4) permitted
from > 20mm4) to be replaced in the works
To be replaced in the works
Resin gall3) 5) Permitted Resin galls are permitted up to 5mm Resin galls are permitted up to 3mm
Knots and faulty points improved by means of knot hole plugs or "ships"3) Not necessary Permitted Permitted
Knots and resin galls improved by means of filler compound3) Not necessary Permitted6) Permitted6)
Insect attack3) Permitted are burrows up to 2mm Permitted are holes up to 2mm Not permitted
Pith Permitted Permitted Pith visibly on the outer lamellas is not permitted
Cracks caused by shrinking3) 5) 7) No limit Up to 4mm Up to 3mm
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
Mould5) Not permitted Not permitted Not permitted
Contamination of the surface5) Permitted Not permitted Not permitted
Distance between fingerjoints No limit No limit On visible remaining outer lamellas, the distance between one another has to be at least 1m
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


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