THE GLUING OF WOOD 
41 
preheating the wood usually results in weak joints, especially if the 
glue is of low grade. In commercial practice starved joints (pi. 
10, B) resulting from overheating are more common than chilled 
joints (pi. 10, C) resulting from a lack of heating. Practically all 
types of commercial gluing can be satisfactorily and conveniently 
done if the temperature of the wood is within the range of 70° to 
90° F. (See Tables 7 and 8 for recommended gluing schedules.) 
THE QUANTITY OF GLUE SPREAD 
An excessive glue spread wastes glue, adds more water to the wood 
than necessary, and may cause the wood to slip out of position while 
being pressed. The general relation of quantity of glue spread to 
500 
\400 
I 
<0 
-» — ■ 
„*^ 
1 
1 
\ioo 
1 
« ZO 40 6o ao /OO /20 /4-Q 
Quantity of Q/i/e 5~pre>crc/ — Pounc/s (mixed aiue) 
per /poo Square Feet of G/ue Line Area 
Figure 11. — Effect of quantity of glue spread on joint strength of vegetable glue. 
Tests were made on three-ply cross-banded panels with all plies of ^-inch birch. 
Values are averages of 25 to 230 specimens 
joint strength is illustrated in Figure 11, which is based upon labora- 
tory tests upon plywood glued with vegetable glue. With casein 
and vegetable glues, spreads of 65 pounds of wet glue per 1,000 
square feet of surface give high strength values when the other 
gluing conditions are favorable. This is equivalent to a glue spread 
of 45 square feet of single glue line per pound of dry glue, where 
a mixture of 2 parts of water to 1 part by weight of glue is used, 
or it is equivalent to 48 square feet for a mixture of 2% parts of 
water to 1 part by weight of glue. For the best results under a wide 
range of conditions, a glue spread of 75 pounds per 1,000 square feet 
is recommended. This is equivalent to 37 square feet per pound of 
dry glue mixed 2 to 1, or 40 square feet per pound of dry glue mixed 
2y 8 to 1. Thicker spreads than 80 pounds of wet glue per 1,000 
square feet are unnecessary under ordinary gluing conditions. If 
the strength requirements of the glued product are not very high, 
