(G.) Paint brushes, or other brushes in which the bristles are set in glue, are not suitable for use in hot glue, and those made especially for this purpose should be purchased. For very small brushes, a strip of basswood bark may be soaked and pounded about half an inch from the end; these are satisfactory for small work.
66. How to use glue.—(A.) Glue should be used as hot as possible, and of about the consistency of cream. The pieces to be glued should be heated thoroughly and the gluing done in a warm room.
(B.) In factories, where it is possible, the gluing is done in a specially fitted room which contains all necessary appliances. Vertical and horizontal coils of steam pipes surround the room, both to furnish heat for the room, and for the purpose of heating the material to be glued, which should be so hot that the hand cannot rest upon it for more than a few seconds. In a room of this sort, the temperature is maintained at from 110° to 130° F.
(C.) If the best possible results are wanted, a scratch plane should be used. This is a tool similar to a smoother, only its cutter is nearly vertical, and it has teeth like a fine saw which will scratch the wood, thus giving a better hold for the glue.
(D.) It is important that all clamps, handscrews, and other appliances which are likely to be needed should be set as nearly as possible the desired size, and so arranged as to be reached easily, for when the glue is applied, there should not be the slightest hesitation or delay in getting the work together and the clamps on. The utmost speed and surety of motion is absolutely necessary in using hot glue; therefore everything during the process of the work should be foreseen and provision made for it before the glue is applied, for if the glue is even slightly chilled, the work will not be so well done, and the efficiency of the glue will be greatly diminished. A novice should never attempt more than the simplest work, unless working with a competent man.
(E.) The glue should be spread rapidly and evenly with a brush of suitable size,—a large one for broad surfaces and a small one for small work. Glue should not be thrown about wastefully; enough should be used to cover the surface completely but not thickly.
(F.) In using handscrews, it is of the greatest importance that the jaws be kept parallel as described in Topic 59; care must be used that more strain is not placed upon the handscrews and clamps than is necessary to bring the joint together.
(G.) Cold or liquid glue has supplanted hot glue in furniture repairing, gluing up intricate work, and in places where it is impracticable to use hot glue either on account of its setting too rapidly, or where heat is not available. Liquid glue does not hold as well nor as permanently as hot glue when properly used, but for many kinds of work it is perfectly satisfactory.
(H.) In gluing rosewood, or other woods of a greasy nature, the glue should be thinned with vinegar, which will cut the grease. Another method of making glue hold on wood of this sort is to chalk both members of the joint thoroughly, and let it stand for two or three hours, when it should be wiped off. This absorbs the grease on the surface of the wood, which allows the glue to take hold. In all gluing, do not allow the bare hand to touch the joint any more than necessary, as the grease and perspiration will prevent the best results from being obtained.
67. The testing of sandpaper.—(A.) Sandpaper is made by covering paper with a thin layer of glue, over which is spread evenly a layer of ground flint or glass; over this is spread another coating of glue, which firmly fastens the sand to the paper.