Glazing

Introduction

The use of glass in the building industry has increased greatly over the last few decades. The versatility of flat glass - the genetic term used to describe unbowed glass used in the glazing of windows and doors -has enabled it to be used in many ways, which ultimately enhance the quality of life. Glass has been adapted to reduce both heat loss and noise with double and triple glazed units. Laminated and toughened glass offers greater safety than ordinal), sheet and float glass; laminated glass gives the added advantage of increased security protection. Wired glass prevents the spread of flames, while solar control glasses (specially coated and tinted) help reduce the effects of radiant heat from the sun. Patterned and obscured glass afford a greater degree of privacy together with a decorative quality. 

There are also numerous materials for the fixing of glass to frames, from traditional linseed oil and whiting putty, timber beads screwed or nailed to frames, to modem sealants, non-setting compounds, mastic tapes and so on. We shall, however, be concentrating on the basic methods by which glazing is fixed to frames. 

Estimating for glazing 

In order to estimate the costs of a particular item of work accurately, it is necessary to have details of the following: 

• Glass type, quality, thickness and normal maximum sizes of sheets
• Type of surround to which glass is to be fixed, e.g. wood, aluminium, uPVC 
• Glazing compounds, beads, etc. and their suitability for work in connection with a particular surround. 

Wastage varies dependent on whether glass is bought pre-cut to the required size, or in large sheets, which are cut to size on site, or in the contractor's yard. Typical wastage figures are as follows: 

Pre-cut glass 5% 

Uncut glass 10% 

Glazing compounds and sundries 10% 

Under the rules laid down in SMM7 for glazig, standard plain glass is grouped into two main categories of pane area: less than 0.15 m2, and from 0.15 to 4 m2. Non-standard plain glass, that is any glass (other than special glass) which is drilled, brilliant cut or bent, or is 10 mm thick or more, or is in panes greater than 4m2, gives rise to another category of pane area: more than 4 m2. 

The variance in pane sizes within the category 0.15 to 4 in can be great. Therefore the estimator will assess the average pane size and allow outputs accordingly. Although the estimator may choose to determine his own categories and relate the relevant outputs, etc. to those categories, it is convenient in our case to adopt the categories used in SMM6. Table 1 shows typical requirements for glazing compound. Table 2 shows outputs for a tradesman for cutting and glazing. 

Types of glass

Clear sheet glass 

Sheet glass, because of the nature of its manufacture, never has two surfaces perfectly parallel or flat, it thus distorts transmitted and reflected light. This glass is manufactured in thicknesses of 2, 3, 4, 5 and 6 mm (the 2 mm thickness is not recommended for general glazing). Clear sheet glass has generally been superseded by float glass. 

The quality of the glass used depends on the class of work desired. BS 952 recommends three qualities: 

Ordinary glazing quality OQ 

Selected glazing quality SQ 

Special selected quality SSQ 

Float glass

This is a truly flat glass, giving undistorted vision. It is formed by floating a continuous ribbon of molten glass onto liquid metal at a controlled rate and temperature. This glass is manufactured in general glazing quality and selected quality in thicknesses of 3, 4, 5, 6, 10 and 12 mm.

Polished plate glass

Polished plate glass has both surfaces ground and polished and in parallel, giving undistorted vision. It has generally been superseded by float glass, which has the same qualities at reduced cost. This glass is manufactured in thicknesses of 5, 6, 10 and 12 mm, although it can be manufactured up to 38 mm thick. 

Patterned glass 

Patterned glass is a rolled glass. During manufacture a pattern is formed on one face of the glass while the other face is left flat. The pattern makes the glass partially or totally obscure. This glass is manufactured in thicknesses of 3 and 5 mm. 

Roughcast glass 

Roughcast glass is a translucent glass which has a textured surface introduced by the rollers during manufacture. It is manufactured in thicknesses of 5, 6 and 10 mm. 

Wired glass 

Wired glass has wire mesh incorporated during the rolling process. Wired glass may have a cast finish or be subsequently polished. It is manufactured in thicknesses of 6 mm polished or 7 mm cast. 

Laminated glass 

This glass consists of a sandwich construction of two or more sheets of ordinary glass, between which are bonded interlayer(s) made of resilient plastic material. It is manufactured in thicknesses of 4.4, 5.4, 6.1, 6.4, 6.8 and 8.8 mm. 

Toughened glass 

Toughened glass is formed by heat-treating clear, patterned and other types of glass (wired glass cannot be treated in this manner). It is manufactured in thicknesses of 4, 5, 6 and lOmm. 

Table 01 and 02