for glazing aluminum and steel sash either inside or outside. It should be applied as recommended by the manufacturer.  Metal-sash  putty  should  be  painted within  2  weeks  after  application,  but  should  be thoroughly  set  and  hard  before  painting  begins. There  are  two  grades  of  metal-sash  putty:  one  for interior  and  one  for  exterior  glazing.  Both  wood-sash putty and metal-sash putty are known as oleoresinous caulking compounds. The advantage of these materials is  their  low  cost;  their  disadvantages  include  high shrinkage,  little  adhesion,  and  an  exposed  life expectancy of less than 5 years. Elastic  Compounds Elastic  glazing  compounds  are  specially  formulated from  selected  processed  oils  and  pigments,  which remain plastic and resilient over a longer period than the common  hard  putties.  Butyl  and  acrylic  compounds  are the most common elastics. Butyl compounds tend to stain  masonry  and  have  a  high  shrinkage  factor. Acrylic-based  materials  require  heating  to  110°F  before application.  Some  shrinkage  occurs  during  curing.  At high temperatures, these materials sag considerably in vertical  joints.  At  low  temperatures,  acrylic-based materials become hard and brittle. The y are available in a wide range of colors and have good adhesion qualities. Polybutane Tape Polybutane tape is a nondrying mastic, which is available  in  extruded  ribbon  shapes.  It  has  good adhesion qualities, but should not be used as a substitute or replacement for spacers. It can be used as a con- tinuous bed material in conjunction with a polysulfide sealer compound. This tape must be pressure applied for proper  adhesion. Polysulfide  Compounds Polysulfide-base products are two-part synthetic rubber compounds based on a polysulfide polymer. The consistency of these compounds after mixing is similar to that of a caulking compound. The activator must be thoroughly  mixed  with  the  base  compound  at  the  job. The mixed compound is applied with either a caulking gun  or  spatula.  The  sealing  surfaces  must  be  extremely clean.  Surrounding  areas  of  glass  should  be  protected before glazing. Excess and spilled material must be removed  and  the  surfaces  cleaned  promptly.  Once polysulfide  elastomer  glazing  compound  has  cured,  it  is very difficult to remove. Any excess material left on the surfaces after glazing should be cleaned during the working time of the material (2 to 3 hours). Toluene and xylene are good solvents for this purpose. Rubber  Materials Rubber  compression  materials  are  molded  in various shapes. They are used as continuous gaskets and as  intermittent  spacer  shims.  A  weathertight  joint requires that the gasket be compressed at least 15 percent.  Preformed  materials  reduce  costs  because careful cleaning of the glass is not necessary, and there is no waste of material. MEASURING AND CUTTING GLASS Always measure the length and width of the opening in which the glass is to fit at more than one place. Windows are often not absolutely square. If there is a difference between two measurements, use the smaller and then deduct 1/8 inch from the width and length to allow for expansion and contraction. Otherwise, the glass may crack with changes of temperature. This is especially  true  with  steel  casement  windows. Cutting   glass   is   a   matter   of   confidence-and experience. You can gain both by practicing on scrap glass  before  trying  to  cut  window  glass  to  size. Equipment required for glass cutting consists of a glass cutter, a flat, solid table, a tape measure, and a wood or metal T-square or straightedge. Look at figure 4-28. You should lightly oil the cutting wheel (view A) with a thin machine oil or lubricating fluid. Hold the cutter by resting your index finger on the flat part of the handle, as shown in view B. To cut a piece of glass, lay a straightedge along the proposed cut, as shown in view C. Hold it down firmly with one hand and with the glass cutter in the other, make one continuous smooth stroke along the surface of the glass with the side of the cutter pressed against the straightedge (view D). The objective is to score the glass, not cut through it. You should be able to hear the cutter bite into the glass as it moves along. Make sure the cut is continuous and that you have not skipped any section. Going over a cut is a poor practice as the glass is sure to break away at that point. Snap the glass immediately after cutting by placing a pencil or long dowel under the score line and pressing with your hands on each side of the cut (view E). Frosted or patterned glass  should  be  cut  on  the  smooth  side.  Wire-reinforced glass can be cut the same as ordinary glass, except that you will have to separate the wires by flexing the two pieces up and down until the wire breaks or by cutting the  wires  with  side-cutting  pliers. 4-22