Appearance
Green oak is a pale yellow colour with streaks of pink. As the boards dries the oak takes on a golden colouring. Boards will contain regular sound knots and may contain the occasional worm hole.
Weathering
As green oak weathers, the colour will change to a silver-grey. On shaded elevations or in areas of higher pollution the oak may change to a colour closer to black than grey. In semi-shaded areas such as under eaves, the exuding tannin may leave unsightly stains. As the oak dries out the boards will shrink and are likely to distort to some extent, resulting in a rustic appearance.
Desired service life
Occasionally wet 30 yrs. Frequently wet 15 yrs.
Movement class
Large
Resistance to impact
Medium to high
Working properties
Green oak is generally easy to work and takes fixings satisfactorily, but becomes increasingly difficult as it dries.
Density
670 – 760 Kg / m3 (When dry)
Extractives
Oak contains tannic acid, which will corrode ferrous metals. When the two come into contact, a blue sludge is formed that will stain the oak and anything else it meets. All fixings used in conjunction with green oak should be stainless steel. Tannic acid could also leave unsightly brown stains in the surface of the cladding and will stain any porous materials below the cladding. The reactivity of tannin makes oak cladding unsuitable for polluted areas and shaded areas.