Choosing glass

Glass is made in a variety of thicknesses. The choice depends on the size of sheet and the degree of exposure to wind and consequent suction loads on the surface. Most domestic glazing uses glass 4mm thick.

Glass is now sold by thickness; it was formerly sold by weight. The main basic thicknesses are: 2mm, 3mm, 4mm, 5mm, 55mm and 6mm. Special glass is required for greenhouses, the 3mm grade being most suitable.


There are two basic types of clear glass – sheet and float.

Sheet Glass

Sheet glass is made in three grades:

OQ-ordinary quality;

SQ-selected quality;

SSQ-special selected quality.

For general glazing purposes, the OQ grade is suitable. Sheet glass used for normal glazing work is a clear drawn glass. Since the opposite sides of a pane are never perfectly flat and parallel, some degree of distortion is inevitable. Sheet glass is commonly used for domestic glazing and is available in thicknesses from 3mm to 6mm.

Float Glass

Float glass is made by floating the liquid glass over a surface of molten tin. This produces a glass similar to plate glass, which it has replaced. Float glasses are made in thicknesses from 5mm to 25mm. As this glass is free from distortion and is strong, it has many applications, including those of glazing large picture windows and for such things as glass table tops.

Float glass is also produced in plain or tinted decorative forms by using various processes, including acid etching, electro-floating and sandblasting. Additional dec- orative effects are obtained by the introduction of certain materials into the molten glass mix, to alter its light and heat-transmission characteristics.

Patterned Glass

Patterned glass includes glasses with several different decorative finishes and is frequently used for ‘modesty’ glazing in bathrooms and toilets.

A typical example is rough-cast glass, which is smooth on one side and obscured on the other. These glasses are usually produced by passing molten liquid glass through rollers, to produce patterns in plain and tinted versions. Thicknesses are generally between 3mm and 5mm. The degree of transparency and light diffusion depends largely on the type of pattern used.

Wired Glass

Wired glass has a metal mesh embedded in it. This mesh helps to hold the glass together and reduces the risk of injury from falling glass.

It is also accepted as a fire-retardent material. The mesh may be square (Georgian) or diamond pattern. Such glass is often used in porches and garage roofs, but as it is difficult to cut if re-used it is best bought ready cut to size. It is made in 6mm thicknesses only.

Toughened glass

Float, sheet and even some patterned glasses can be toughened by a special process which can increase the strength of the glass by four or five times. It is suitable for doors and similar areas where there is a danger of impact, since it shatters into granules instead of sharp splinters if broken.

Another type of glass is a strong, translucent glass used mainly outdoors for carports and the like, though it can be used indoors.

Solar Control Glass

Solar-control glass reduces the transmission of heat, light and glare from sunlight. It is available in a range of colours in float, laminated, rough-cast and patterned form.

Mirrors are also made from float glass of SQ grade. This is moisture-proofed, silvered and edged in a variety of ways, by machine and by hand grinding.


When you order figured glass, always give the height first and the width next. This is critical, for instance, in the case of ribbed glass, since the pattern should run from top to bottom. If you give the width first, the pane would end up with the ribs running from side to side.

In measuring up irregular openings, such as arched window frames, it is always safer to make up a template in hardboard or plywood. If the opening is to be glazed with figured glass, mark the side which is going to be towards the outside of the house ‘face’. If this is not done, the ‘wrong’ side of the cut pane may become a dirt trap and be difficult to clean.


Glass should be stored vertically at an angle of 25° in a dry place. Lean the panes on two wooden slats propped against the wall and place rag or newspaper pads under the top edge of the panes to stop them from coming into direct contact with the wall. The surface of glass is easily spoiled by dust and moisture, before or after glass is fitted, so protection or regular cleaning is desirable if glass is to remain in the best condition.

10. November 2011 by admin
Categories: Featured, Handyman Tips | Tags: , , , , , , , , , | Comments Off on Choosing glass


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