Steaming has very much the same effect upon timber as boiling, but the timber is said to dry sooner after the former process,1 and it is by some considered that steaming prevents dry rot.
Mr. Britton says, however, "no doubt boiling and steaming partly remove the ferment spores, but may not destroy the vitality of those remaining."
Hot-air Seasoning, or desiccation, is effected by exposing the timber in an oven to a current of hot air, which dries up the sap.
This process takes only a few weeks, more or less, according to the size of the timber.
Great care must be taken to prevent the timber from splitting, the heat must not be too high, and the ends should be clamped.
Desiccation is useful only for small scantling; the expense of applying it to larger timber is very great; morever, "as wood is one of the worst conductors of caloric, if this plan be applied to large logs the interior fibres still retain their original bulk, while those near the surface have a tendency to shrink, the consequence of which would be cracks and splits of more or less depth." 2
Desiccated wood should not be exposed to damp before use.
Mr. Laslett says that during this process ordinary woods lose their strength, and coloured woods become pale and wanting in lustre.
M'iNeile's Process is one that has been some few years in operation.
It consists in exposing the wood to a moderate heat in a moist atmosphere charged with various gases produced by the combustion of fuel.
The wood is placed in a brick chamber, in which there is a large surface of water to produce vapour.
The timber should be stacked in the usual way, with free air-space round every piece; about 1/3 of the whole content of the chamber should be airspace.
Under the chamber is a fireplace.
The fire having been lighted, the products of combustion (among which is carbonic acid gas) circulate freely in a moist state around the pieces of timber to be seasoned.
The time required varies with the nature of the wood.
Oak wainscot planks 2 inches thick take from 5 to 6 weeks.
Deals 3 inches thick something less than a month.
Flooring boards and panelling about 10 days or a fortnight.
"The greener the wood when first put into the stove the better. As a rule, if too great heat be not applied, not a single piece of sound wood is ever split, or warped, or opened in any way. The wood is rendered harder, denser, and tougher, and dry rot is entirely prevented. The wood will not absorb by subsequent exposure to the atmosphere nearly so much moisture as does wood dried by exposure in the ordinary way, hence it is better for all purposes than air-dried wood." 1
The process seemed to have no injurious effects upon the appearance or strength of the timber.
It has been adopted by some of the principal firms in London and elsewhere.
Smoke-drying. - It is said that if timber be smoke-dried over a bonfire of furze, straw, or shavings, it will be rendered harder, more durable, and proof against the attacks of worms. In order to prevent the timber from splitting and to ensure the moisture drying out from the interior, the heat should be applied gradually.
Many woods require a second seasoning after they have been worked.
Floor boards should, if possible, be laid and merely tacked down for several months before they are cramped up and regularly nailed.
Very often a board that seems thoroughly seasoned will commence to warp again if merely a shaving is planed off the surface.