Civil Engineering Reference
In-Depth Information
Glass and methods of installation
Float glass is normally used in windows, though machine glass is still in pro-
duction in some European factories. Cast glass is used indoors, often as a dec-
orative product which doesn't need to be transparent. There are various types
of energy glass, security glass, sound-insulating glass and fire-proof glass.
Energy glass is often coloured or covered with a metallic oxide. Security glass
is specially hardened or laminated with a foil of polyvinyl butyral between the
sheets of glass. Sound-insulating glass is also laminated in two or more layers.
Fire-proof glass usually consists of several layers laminated with sodium sili-
cate.
The temperature of glass has to be even across its whole surface when it is cut,
otherwise tension can occur within the glass and lead to splitting. Depending
upon the level of insulation required, there will be one, two or more layers of
glass in windows. There are several ways of achieving this. The easiest is to hinge
two timber windows together, which is a traditional way of constructing win-
dows in Scandinavia. The sheets of glass are placed in the frame with putty based
on acryl plastic or linseed oil. Internal glazing can be mounted with special bead-
ing of wood or aluminium. Before using linseed oil putty on a window frame, the
timber must be treated with oil or paint, otherwise the linseed oil will be
absorbed by the window frame and the putty will crack.
Sealed units have become the most common type of glazing in the building
industry. These consist of two or three sheets of glass with a layer of air sealed
between them. The air can be replaced with an inert gas, such as argon, which
improves the thermal and sound insulation of the window because it circulates
more slowly than air. The sheets of glass are connected by plastic or metal sections
and sealed with elastic, plastic-based mastic. Until the late 1980s polychlorinated
biphenyls, PCBs, were widely used, but today silicones are more common. Sheets
of glass can also be welded together. The sealed units are usually fixed into a win-
dow frame with beads of wood or aluminium, together with rubber packing.
More recently, alternatives to glass have appeared on the market. These are
mainly polymethylmetacrylate (plexiglass) and polycarbonate, which are main-
ly used in roof lighting, greenhouses and conservatories. The sheeting products
are mounted in a similar way to the sealed units.
Normal glass is based on raw materials with rich reserves, while the produc-
tion consumes large amounts of energy and produces pollution. Ingredients of
plastic and metal oxides used also cause problems. Transparent plastic products
are based on oil, and they generally consume high levels of primary energy and
produce pollution.
Plastic and glass products probably present no problem in the indoor climate,
even though there may be small emissions from plastic-based putty, mastics and
sealants, depending upon the type of plastic and the mounting technique. Little
