1. That the dead shores should not stand over cellars or such places. It is better to continue the needle to such a length that solid ground is reached, and the needle can then be strutted from the dead shore.
2. That extra needles should be placed under chimney breasts, should there be any in the wall which is to be supported. The same applies where corbels, piers, &c. occur.
3. Sleepers and shores should be so placed that they do not interfere with the proper construction of the new foundations or portions of the building.
4. The inside shores should be carried freely through the floors until a solid foundation is reached.
5. The removal of the shores after the alterations have been made is one requiring great care. It should be remembered, that while the work is new it cannot offer its greatest resistance to its intended load. Time should therefore be given for the work to well set, and then the timbers, eased gradually by the wedges being loosened, should be finally taken out.
6. The raking shores, if used in conjunction with underpinning, should be left to the last.
CHAPTER IV
TIMBER
Classification and Structure.—A short study of the classification and structure of wood will be useful, as it will enable the scaffolder to use material free from the inherent defects of its growth.
The trees used by the scaffolder are known as the exogens or outward-growing trees.
The cross section of an exogenous tree shows, upon examination, that the wood can be divided into several parts. Near the centre will be seen the pith or medulla, from which radiate what are known as the medullary rays. These in the pine woods are often found full of resinous matter.