Civil Engineering Reference
In-Depth Information
reinforcement. When they are mounted the joints must be filled. The filling mate-
rial is, almost without exception, based on plastic binders, mainly PVAC glue or
acrylate glue.
Cement-based sheets
Cement-based sheets are relatively new on the market. The first cement fibre
sheets came in Japan in 1970. The sheets are non-flammable and are particularly
strong. They can be used internally or externally without rendering as they will
withstand frost. A binding of cellulose fibres or wood chippings from spruce or
birch give the best results. The amount of wood chippings is usually about 25 per
cent by weight. They are treated with a substance which reacts with lime (see
'Woodwool slabs - production and use', p. 284), and then mixed with Portland
cement and water, after which the sheets are formed in a hydraulic press for
seven to eight hours, then set in a special curing chamber.
Calcium silicate sheets
These are used as both internal and external cladding. They are non-flammable
and strong. The sheeting is produced with up to 92 per cent by weight of quartz
mixed with lime and a little cellulose fibre as reinforcement. Vermiculite can be
used as aggregate.
Plasterboard
Plasterboard was first produced about 100 years ago. The usual sheeting prod-
ucts are used mainly for internal wall cladding, either covered by wallpaper or
thin fibreglass woven sheeting for painting. Gypsum products also have an
important role as climatic products (see chapter on 'Climatic materials'). The
standard products are manufactured from 95 per cent gypsum with fibreglass
reinforcement (about 0.1 per cent by weight). The following substances are also
added to a total of about 1 per cent by weight: calcium lignosulphate, ammoni-
um sulphate and an organic retardant. The sheets are covered with thin card-
board which is glued with potato-flour paste or PVAC glue. Pure gypsum sheet-
ing is not particularly strong, but some sheets contain a large percentage of wood
shavings, which increases strength.
The mineral sheets are based on raw materials with rich reserves. Gypsum as a
by-product of power stations is used a great deal in the production of plaster-
board.
The use of primary energy for calcium silicate products is low, but is much
higher for gypsum and cement products.
Pollution from the production of sheeting is relatively low, calcium silicate
sheeting causing the least. When built in, there are no problems with these
materials, although asbestos may be found in older products. Calcium silicate
