106 GREENHOUSES 



the glass is sealed by a thin film underneath 

 and along the sides of each pane. This 

 method has been developed because experi- 

 ence has shown that on roofs putty soon 

 checks and crumbles away when exposed to 

 the weather as in window glazing. 



When glass is lapped, the following meth- 

 od is used. First, the sash bars should have 

 been so placed that the space left for the glass 

 is about one-eighth of an inch wider than the 

 glass. This provides room for the "side 

 putty." (For method of spacing see page 

 87). Sash bars are usually primed when re- 

 ceived from the factory. They are given an- 

 other coat of paint after they are put in 

 place and are then ready for glazing. 



Glazing is started at the bottom of the run. 

 A line of soft putty is first placed in the rab- 

 bets and a pane of glass forced firmly into it 

 until it is imbedded against the bar. A 

 groove is usually provided in the plate to re- 

 ceive the lower edge of this glass to prevent 

 it from sliding down, but if there is no such 

 groove, three or four brads or glazing points 

 are driven for the lower edge to rest against. 



The excess putty is then removed and the 

 next glass forced firmly into place, so that 

 its lower edge laps over and rests firmly on 



