If glue is in flakes or strips, break up into small pieces. Soak the pieces from 10 to 12 hours in cold water. Soak ground glue 1 to 4 hours in cold water. Naturally the thinner the glue the less time required for thorough soaking. The glue should be soaked through thoroughly and not merely moistened on the outside. You can determine whether the soaking has been completed by breaking a piece in two and noting conditions at the centre. If pieces are permitted to stick out beyond the level of the water, the natural result is that such pieces will be only partially softened. As the melting proceeds, these will slip to the bottom of the kettle, and in order to melt them long heating and high temperature are required. This means damaging the strength and adhesiveness of the glue.
In soaking ground glue it is a good plan to keep stirring as the glue is added to the water in the soaking vessel, as this helps to keep the fine particles of glue immersed in the water, instead of floating on the top. This is true also of thin-cut, high test glues.
USE ONLY PURE, COLD WATER
In soaking and thinning glue, use only pure, cold water. Unless heater is provided with pure water attachment or pure water chamber, avoid using water from the glue-heater. Do not use water from boilers, for such water contains pipe-rust, acids from boiler compounds, sediment, and other matter extremely harmful to glue. See to it that all soaking vessels are scrupulously clean.
TESTING GLUE BY WATER ABSORPTION
The soaking of glue in cold water before using is employed in some factories as a basis for comparative test of working quality. The amount of water absorbed may vary as much as 10 ounces in half a pound. Other things being equal, the glue that absorbs the most water is of course the cheapest to use. As a comparative test, melt up say 10 pounds of glue and see how much work it will do compared with the glue you are now using.
A SIMPLE GLUE-TESTER FOR DETERMINING WATER ABSORPTION
Apparatus for Testing Glue in Solution