26. Preservation Of Timber

For ordinary building construction the best means for preserving timber from decay is to have it thoroughly seasoned and well ventilated, and if these conditions are secured there will be little danger of rot.

For the majority of buildings designed by the architect it is practically impossible to obtain thoroughly seasoned lumber, but much can be done to secure ventilation.

* "Notes on Building Construction," Part III.

Large beams and girders are better built up and cased, and posts should be bored longitudinally, as described in Section 15.

When built into masonry walls a space should be left around the timber to provide ventilation.

Wherever beams have to be enclosed air-tight it is desirable that some means of ventilation be provided if possible, particularly if the wood be not thoroughly seasoned or there is any chance of its becoming damp. In all outside woodwork care should be taken to form the joints so as not to afford a lodgment for moisture. All woodwork exposed to the atmosphere is generally protected by paint or oil, but they should not be applied while the wood is wet or damp, nor, if practicable, while it is green. All woodwork in contact with outside masonry should have the back painted.

Posts to be set in the ground should either be dipped in coal tar or else the parts to be buried should be charred. Timber that is to be used in sea water for wharfs, etc., and in places where it will be subject to moisture, but not kept constantly wet, such as piles and sleepers, should be impregnated with creosote under a pressure of from 30 to 40 pounds per square inch. There are several processes for preserving timber, but filling the pores with creosote is admitted to be equal to any, and for protecting wood against the teredo or ship worm it is at present admitted to be the most valuable process.