The construction of a wooden sash has been described at page 196, Part I., and it has been there explained that the styles and bars of the sash have rebates formed upon their inner sides to receive the edges of the panes with which they are to be glazed.
The glass is cut with a diamond into panes. The dimensions of these should be a little less both ways than the distances between the sides of the rebates upon which they are to rest, so that the edges of the glass nowhere actually touch the woodwork of the sash, and any jar received by the latter is deadened by the intervening putty before it is felt by the glass.
A layer of putty is spread over the narrow part of the rebates, upon which the glass is firmly bedded. This is called the back putty; as the glass is pressed upon it the superfluous putty is squeezed out round the edges of the panes, and cut off on the inside.
1 Seddon's Builders' Work.
This superfluous putty should not be cut off for four or five days, as its removal may disturb the front putty.
The back putty is sometimes omitted in inferior work. When plate-glass is used it is not required.
The glass is then front-puttied, the rebate is stopped, that is filled in with putty to a triangular section, as shown in Fig. 373. This soon hardens, and keeps the glass secure.
Care must be taken that the putty does not project beyond the front of the rebate, so as to be seen from the inside of the window.
Large panes of plate-glass are not back-puttied, for it would be useless in the case of large and heavy panes to attempt to compress the putty when bedding the pane.
In very large and heavy panes copper brads or sprigs are driven in to secure the glass more firmly before it is front-puttied, or the glass may be secured by beads or mouldings secured to the bars or frames of the sashes, as in Fig. 374.
Large panes of plate-glass in doors are sometimes bedded in wash-leather or vulcanised indiarubber, one piece glued to the inside of the rebate the other placed on the reverse side of the glass (see % i, Fig. 374), so as to deaden the effects of concussion.
Plate-glass is thick, and keeps a room warm, but is expensive, and therefore used only in houses of a superior class.
The glazing is generally done after the plastering is finished and the floors laid, and before the painting, the sashes being primed however before the glass is put in, in order to prevent the wood from absorbing the oil out of the putty. The surfaces of all puttied joints should be painted, to prevent the oil from evaporating.
Iron sashes have bars of similar shape to that of wooden sash-bars, and are glazed in the same way, particular care being taken that the glass does not touch the iron, in order to avoid the risk of its being broken.
As already mentioned (see p. 97), skylights and other inclined sashes have no horizontal sash-bars ; the panes are made to overlap, as shown in Fig. 188. When they are large and heavy, any tendency for them to slip down is prevented by hanging the tail of each on to the head of the pane below by means of a zinc or copper tingle, as shown by the dark line in Fig. 188.
"Considerable overlap is necessary to prevent leakage, for the overlapping surfaces can seldom be brought into direct contact; consequently wet is held and drawn up by capillary attraction, and if the lap is not sufficient it will drip over the heads of the under sheets, and, moreover, get blown up by the wind; therefore it is better, if possible, to keep the overlapping surface far enough apart to prevent any capillary action coming into play. The tails of the panes are frequently cut to a point or rounded to throw the water off better, as well as to turn it away from the sash-bars." l