Wood-working for Beginners: A Manual for Amateurs

by Charles G. Wheeler

Glue loses strength by repeated meltings, so do not dissolve too much at a time, and after heating it over two or three times throw away any that is left in the glue-pot, cleaning the latter thoroughly. On work which you are very particular about mix fresh glue each time.[46]

You can make a good glue-brush of a stick of rattan. Soften the end in hot water and pound it with the hammer until the fibres separate. For corners, cracks, holes, and the like use sticks, which you can whittle to any required shape.

Although apparently too simple an operation to need much explanation, and often ignored in books on wood-work, as if anyone could of course glue two pieces together, the operation, to be really successful, calls for more knowledge of the principles involved than beginners or amateurs usually possess. Do not daub a thick layer of lukewarm glue on the pieces, and then slap them together as you would make a sandwich, after the usual domestic fashion. Done in this way the pieces often stick for a while, but there is nothing certain about it.

We have seen that wood is full of little holes (pores, as they are commonly called), or spaces between the fibres (see Fig. 6). The glue becomes worked into these little pores and that is what gives it such a firm hold on the wood, somewhat as plastering is forced (purposely) into the cracks between the laths.

So you must have the glue thin, that it may fill these little cavities and get a "grip" on the wood; you must have it hot, that it may the more easily penetrate these open spaces before it becomes chilled; you must have the wood warm, that the glue may not be chilled and begin to set before it has a chance to penetrate the interstices of the wood; and you must press the pieces together so hard as to expel the body of glue from between them, forcing it into the pores and squeezing outside what will not go in, to be wiped or scraped off afterward. For what you want is not to have the two pieces held together by a layer of glue between them, lightly sticking to each surface and separating the two in proportion to the thickness of the layer; but to have the two surfaces as close together as possible, held so by the tenacity of the glue reaching from the cavities of one surface to those of the other. The closer the surfaces are forced together the better, as the glue will be less exposed to the atmosphere.

You will see from all this that gluing should be done in a warm room of an even temperature.

While with hot glue it will not do to change the relative positions of the pieces after putting together, you can have considerable time to get them in position if the liquid or cold glue is used. Where several places in the same piece of work have to be glued together at the same time, it is frequently very hard to get around with the hot glue before that first applied has begun to set, unless you have help. In such cases, cold glue is a great convenience. If your shop is not warm or if you cannot have your glue hot, you had better use the liquid glue. It takes much longer to set than the other. In cold weather it should be slightly warmed. It can be thinned with vinegar or acetic acid, or what you wish to use at once may be thinned with water. Do not pour water into the can of glue, as it will not keep so well.

You will also readily see that it is much easier to make good glued joints in soft wood than in hard, for the former is more readily squeezed to a fit by the clamping, while with the latter it is quite essential that the pieces should fit with extreme accuracy before clamping (see note under Clamps).

Before beginning to glue have everything laid out, fit the pieces together, clamp them up just as if you had put on the glue, and see that everything comes together right—i.e., rehearse the gluing process before using the glue itself. This is a very important point, particularly when there are several pieces to be glued, for you will have no time to waste after you have begun to use the glue.

Do not spread the glue on too thick. Take the dirt off both pieces, then, while putting the glue on one, have the other warming slightly at the fire. The moment the glue on the brush leaves the glue-pot it begins to cool. If it fairly begins to set before you get the two pieces together, your joint will not be good. You will have to take it apart, scrape off all the old glue, and begin over again. So you will see there is no time to be lost when once you begin and it will be too late then to correct any mistakes in the fitting of the wood-work. Good workmen always put the work together and take it apart again before gluing.