Civil Engineering Reference
In-Depth Information
Wood fibre boards
The manufacture of wood fibre boards is described in the following chapter. The
porous products, softboards, are used for wind-proofing and have bitumen
added in a proportion of approximately 12 per cent by weight. Hardboards are
used for internal resistance to vapour and as a waterproof membrane under roof-
ing (exterior), the latter usually impregnated with bitumen in a proportion of 5.5
per cent by weight. The normal thickness for softboards is 12 mm, but it is pos-
sible to manufacture thicker and lighter boards. With thicker boards, drying out
is a problem in the wet production process. Hardboards used as climatic prod-
ucts come in thicknesses of 3-5 mm.
These products have a relatively high use of primary energy. As waste, the
products containing bitumen have to be specially disposed of.
Cellulose fibre
Cellulose fibre consists of torn-up recycled paper or pulverized pulp. The fibre is
treated with fire retardants and is used on site as loose fill. The proportion of
chemical additives is as high as 18-25 per cent. These are partly fire retardant,
partly to hinder mould and partly binder. The most commonly used compound
is boric acid and borax. The fibre also contains traces of silica, sulphur and calci-
um from fillers used in the newspaper.
More recently, cellulose fibre mat-
ting has been manufactured using
pure cellulose glue. Cellulose strips
have also been manufactured for
filling the space between window
and door-frames and the building
fabric. Building mats and filling
strips are made from fresh cellulose
fibre, and their production requires
tree felling and a higher use of pri-
mary energy.
Loose fill cellulose fibre has been
used as building insulation since the
1920s, and the material's durability
is good as long as it has been placed
in the walls or roof space in the cor-
rect way. This involves applying a
high pressure when blowing in the
fibre, to avoid settling later on.
Figure 14.15: Cellulose fibre.
