LVL Handbook EUROPE

1. LVL AS A CONSTRUCTIONMATERIAL

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

Metsä Wood

resist seismic loads. LVL-Cmembers, in particular, are not sen-

sitive to cracking or brittle failures of connections, so they can

yield and absorb more energy. Full utilization of these proper-

ties 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 be-

come visible due to swelling or shrinkage caused by moisture

variations or sanding. In addition, the scarf-joints of face ve-

neers can sometimes overlap, leaving the joint slightly open.

Due to moisture variations this may also occur later on the sur-

face 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 mela-

mine 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 be-

tween 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 sur-

face 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