Cross laminated timber predominantly uses spruce lamellae as a raw material. The use of fir, pine, larch and Douglas fir is also common. Other softwoods are also permissible for use in load-bearing board layers in accordance with the relevant approval. Timber types not stated in the approvals can be used as decorative, non-load-bearing outer skins.
The bandwidth of available surfaces ranges from surfaces for non-visible use up to visible permanent surfaces with high requirements on their appearance. Various manufacturers have defined manufacturer-specific grades of surface quality for this purpose.
Permissible joint widths are limited for surfaces for visible use (normally known as industrial quality) and the final outer skin is normally composed of single-layer or triple-layer boards for residential areas. This leads to high quality, joint-free surfaces. Outer skins made of boards also take into account additional grading criteria such as loose dead knots, resin pockets, heart shake and discolouration. Outer surfaces of extremely high quality can be produced through the use of special timber types such as fir or stone pine.
Cross laminated timber is available with planed or sanded surfaces. Surfaces can also be textured (e.g. by brushing). Furthermore, special acoustic profiling is available.
Some approvals allow the use of derived timber boards or parallel laminated veneer boards in the outer skin for special static requirements. If fire protection cladding is necessary, production of elements with outer skins made of fibrous plaster or plasterboard is sometimes permissible. In these cases, deformation must be suitably limited at the limit conditions of usability so that no cracks occur in the cladding.