As before noted, the butt ends of standards tend to decay early. A fairly effective method of preventing this is to bore the butt end upwards to a distance of about 2 feet. The bore, which should be about 1⁄2 inch in diameter, should then be filled with pitch and plugged. The pitch will find its way by capillarity into the pores of the wood and tend to keep the dampness out. Coating the outsides of the butts with pitch is also useful, and a combination of the two would no doubt be effectual; this is especially recommended where the standards have to remain in one place for a long time.
Ladders and fittings that are expensive are generally painted.
The Durability of Wood.—In Young’s ‘Annals of Agriculture’ it is stated that experiments were made on some 11⁄2-inch planks of 30 to 45 years’ growth. They were placed in the weather for ten years, and then examined, with the following result:
Larch—heart sound, sapwood decayed.
Spruce fir—sound.
Scotch fir—much decayed.
Birch—quite rotten.
This experiment, while useful to show the natural resistance of the wood to the weather, does not take into account the effect of wear and tear.
It is almost impossible, in fact, to arrive at any data from which the life of scaffolding timbers can be gauged; but, roughly speaking, poles may be expected to last from six to ten years according to the care exercised. Balk timbers, being usually cut up after a time for other purposes, have only a short life on a scaffold, and therefore seldom decay while in use.
Fig. 62
The Use of Scaffolding Timber.—Poles vary up to 40 and 50 feet in length and up to 8 inches in diameter at the butt end. As decay, which usually commences at this end, sets in, the poles can be shortened and made into sound puncheons or splicing pieces for the ledgers. Balks are used up to 50 or 60 feet in length; and their period of service on a scaffold is often an interval during which they become well seasoned and suitable for other requirements. Putlogs are about 6 feet in length and 4 inches square in cross section, tapering sharply to 21⁄2 by 31⁄2 inches at the ends where required for insertion in the wall. Being of square section they are not liable to roll on the ledgers. They should be split, not sawn, in the direction of their length. The fibres are thus uncut and absorb moisture less easily. This procedure it is found increases their durability. When treated in this manner they are also stronger, as the fibres, being continuous, give greater resistance to a load, the strength not depending wholly on the lateral adhesion, but also upon the longitudinal cohesion. When partly decayed they can be shortened and make good struts for timbering excavations.
The boards are usually from 7 in. to 9 in. wide and 11⁄2 in. to 2 in. thick. Their length averages up to 14 feet. The ends are sawn as [fig. 62] and strapped with iron to prevent splitting. When decayed they are a source of danger for which there is only one remedy—smash them up.