The correct choice of glass depends on the situation and size of the area to be glazed. Glass must withstand the force of wind and suction load over the surface. Other than in very exposed areas, 4 mm-thick glass should be suitable for glazing.
There are two main types of clear glass — sheet and float.
Sheet glass. In Britain the thinner varieties of glass used to be classified according to weight — you would see phrases such as “use 18 oz (or 24 or 32 oz etc) glass for this job.” The number of ounces referred to the weight of one square foot of the glass. In going over to metric, the manufacturers have, sensibly, decided on the thickness of the glass as being the best way of describing it, and the sizes of most interest to the DIY enthusiast are (with the imperial equivalent in brackets): 2 mm (18 oz), 3 mm (24 oz), 4 mm (32 oz) and 6 mm, which used to be described as ¼ in. glass.
The thinnest of these should be used only for picture framing. The 3 mm glass can be used on windows up to about 1 sq yd (say 1 sq metre), whilst for larger windows you should use 4 mm. This latter size will, in fact, do for all the glazing jobs a DIY enthusiast is likely to tackle, for it can be used for panes up to 28 sq ft (about 2.5 sq m) provided that none of the four sides of the glass is greater than 7ft (2.1 m). Over that size, we are dealing with big picture windows and glazing those is a job most people would want to leave to a professional.
As well as the ordinary clear glass, there are toughened varieties for such high risk situations as glass doors, balcony walls, glass roofs etc. Toughened glass, which is made by heating ordinary glass until it softens then cooling it rapidly, is four to five times stronger than ordinary glass, and breaks into harmless chunks rather than splinters. Car windscreens are commonly made of toughened glass in Britain. Another type of glass — wired — is made by rolling two sheets of glass with wire mesh between them. Wired glass is widely used for roof lights. Your glass merchant will advise you on which type of glass you need for specific situations.
A wide range of patterned glass is also available for decorative glazing, and good glass merchants stock a range from which you can choose.
Although it is perfectly possible for the DIY enthusiast to cut glass, perhaps the wisest course is to ask your glass merchant to do it for you. He will charge comparatively little — nowhere near as much as you risk losing by breaking the glass.
Float glass, which is formed by floating molten glass on a bed of molten tin, is a strong high-quality, distortion-free glass, often used in large window areas. It is made in thicknesses from 5 mm to 25 mm. Float glass is now used where plate-glass was formerly employed. It may be plain, textured or tinted.
Patterned glass can provide attractive décor effects and may also be used in situations where obscured glass is needed to give privacy. The amount and character of the light passing through the glass will depend on the colour and thickness of the glass. Patterned glass is normally between 3 mm and 5 mm.
Polished or rough-cast wired glass.
Where strength and safety considerations are particularly important, wired-glass is recommended. Wire mesh is embedded in the glass. If the glass is broken, the mesh helps to hold the pieces together. Wired glass, which also has fire-retardent properties, is suitable for conservatory or porch roofs. It may also be used in doors and the lower portions of large picture-window areas.
Available in 6 mm thickness only, wired glass can be difficult to cut and is better bought pre-cut to size.
Toughened. Sheet, float and some types of patterned glass may be toughened to increase the strength of the material by up to five times. If there is a breakage, the glass shatters into granules rather than sharp splinters. Toughened glass is 6 mm or 10 mm thick.
Diffuse-reflection glass (often called non-reflective glass) is used to cover framed pictures. The glass, 2 mm thick, is coated on one side, so reducing the amount of light reflection and allowing the picture to be seen clearly.
Profilit glass is a strong glass, normally used on exterior constructions such as carports. But this translucent glass may be used indoors too.