This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The best means for preserving timber from decay are to have it thoroughly seasoned and well ventilated. Painting preserves it if the wood is thoroughly seasoned before the paint is applied; otherwise, filling up the outer pores only confines the moisture and causes rot. The same may be said of tarring. Sometimes before the paint is dry it is sprinkled with sand, which is said to make it more durable. For timber that is not exposed to the weather, the utility of paint is somewhat doubtful. Wood used in outdoor work should have those parts painted only where moisture is likely to find a lodgment, and all shakes, cracks, and joints should be filled up with white-lead ground in oil, or oil putty, previous to being painted over. The lower ends of posts put into the ground are generally charred with a view of preventing dry-rot and the attacks of worms. Care should be taken that the timber is thoroughly seasoned, otherwise, by confining the moisture, it will induce decay and do more harm than good. Posts should be put in upside down, with regard to the position in which they originally grew; the sap valves open upwards from the root, and when thus reversed they prevent the ascent of moisture in the wood.
Britton recommends charring the embedded portions of beams and joists, joists of stables, wash-houses, etc, wainscoting of ground-floors, flooring beneath parquet work, joints of tongues and rebates, and railway sleepers. Lapparent applied the method on a large scale by the use of a gas jet passed all over the surface of the timber, but Laslett would only advise its use as a possible means of preventing the generation of moisture or fungus where two unseasoned pieces of wood are placed in juxtaposition.
There are some preserving processes of a special character, not available for application by the carpenter. These are described at length in the Second Series of ' Workshop Receipts,' under the head of Preserving Wood, pp. 456-468. A few simpler methods may be mentioned here. The following will be found a good method of preserving wooden posts, say verandah posts, from decay, and also from the white ant, which is the greatest enemy to carpenters' work in Ceylon. Bore with a 1 1/4-in. auger from the butt-end of the post to a distance that will be 6 in. above the ground-line when the post is set. Then char over a good fire for 15 minutes. This will drive all moisture out of the heart of the butt through the hole bored. Next fill with boiling hot coal-tar, and drive in a well-fitted plug, which will act as a ram, and force the tar into the pores of the wood; the latter thus bocomes thoroughly creosoted, and will last for many years. A post 4 in. x 4 in. may have one hole in its centre; a post 6 in. x 6 in., 2 hole6 side by side; a post 8 in. x 8 in., 3 holes; and one 12 in. x 12 in., 4 holes.
Creosoting timber for sleepers and underground purposes answers very well; also coal-tar is a great means of preserving timber underground from the effects of the white ant, as they will not touch it as long as there is a smell of tar from it. A method used by the natives to protect timber from white ants is - To every gallon of water add 3 oz. croton tiglium seeds, 3 oz. margosa bark, 3 oz. sulphur, 2 oz. blue vitriol; immerse the timber until it ceases to absorb the water, and afterwards take out, and dry in an airy situation.
The following table shows the amount of creosote that will be taken up by some of the harder Indian woods: -
Lb. of Creosote per cub. ft.
Swan River wood (Australia)
Creosote per cub. ft.
Iron wood ...............
It was thought that the forests of Southern India would furnish numerous timbers suitable for sleepers; but these hopes have not been fulfilled, no timber used having been found capable of resisting the combined effects of the heat and moisture of Southern India, and only on the woods of 3 trees is any great reliance now placed, viz. the Erool (Inga xylocarpa), Karra marda (Terminalia glabra), and Vengay (Pterocarpus Marsu-pium). Taking an average of the various native woods used on the Madras railway, the duration of its sleepers has been about 3 1/2 years. Creosoted sleepers of Baltic fir have been found to last nearly 6 1/2 years.
The accepted methods for rendering wood incombustible or reducing its inflammability are described in the Second Series of 'Workshop Receipts,' under the head of Fireproofing Timber, pp. 298-9.