While the edges are warm they are covered with a coating of glue, and rubbed together, so that the superfluous glue is squeezed out. In intricate corners, and places hard to get at, this may be sponged off at once, but generally it is better to leave it to get cold, as it excludes the air and enables the glue to set more firmly.
Glue is required principally in putting framed work together, and in panels; but the less of it that is used the better, even in fixing.
A considerable surface is often covered with boards so united, as in window backs, dados, etc. In such cases keys are generally grooved in across the back, as shown in Fig. 155. These keep the surfaces of the boards in the same plane, and allow them to shrink and expand with changes in the weather.
For all sorts of curved surfaces small blocks are glued together, and then covered with a veneer.
Sometimes wood is bent to the form required, and then blocks are glued on to the back to keep it so.
In order to avoid using large pieces of timber, which can never be so seasoned throughout as to prevent splitting, columns and similar constructions are built up with thin staves, s s, of dry wood, the required support being afforded by an iron column, P, within; and small blocks, b b b, are glued inside the joints to strengthen them, as in Fig. 159.