There are two main types of wood, hardwoods and softwoods. With a few exceptions, hardwoods are expensive, attractive in appearance, more difficult than usual to shape and smooth, wear well and take a lovely polish. Many varieties are not available in long lengths.
Softwoods are often cheaper. They are easy to cut and smooth, and are obtainable in long straight lengths. They may still be attractive in surface finish, and are of course very suitable for work which is to be painted.
All wood contains moisture. A newly felled tree contains a great deal. As the wood is sawn into lengths the water gradually evaporates and the wood shrinks. This process goes on until the wood contains the same percentage of moisture as its surroundings. Obviously, timber left out in the rain will remain damp, whereas timber stored under cover, with freely circulating air, will become dry.
This drying and shrinking is called ‘seasoning’. Ideally, it should be continued till the wood contains about 10% moisture. At this point most of the shrinkage will be completed. The wood is now ‘seasoned’ and can be used for woodwork.
Clearly, if the wood used in furniture were not fully seasoned, and the various parts kept shrinking after assembly, the piece would soon look in a sorry state. It is therefore important to get properly seasoned wood.
Simple inspection cannot tell whether the seasoning is complete or not. Buy from a recognised firm of wood dealers who store their timber in neat stacks under cover, in open-sided racks. Do not buy wood that has been standing outside, even if only for a few days.
Incidentally, age as such has little to do with seasoning. A very old length of wood, quite dark with age, may be totally unseasoned in the real sense, whereas a fresh-cut plank can be force-dried in specially heated kilns and be fully seasoned in a few hours.
However, even fully seasoned wood will continue to shrink, or else may expand again, if it is taken into an atmosphere drier or damper than its storage place at the timber yard. For this reason, always buy your wood a week or more in advance of need, and store it in the room in which it is finally to stand. Here it will lose or absorb moisture, swell or shrink accordingly, and then remain at that size.
Unfortunately for woodworkers, planks of unseasoned timber do not remain flat after sawing. The shrinkage is not regular throughout the wood. The nearer the wood was to the outer bark of the tree, the more it appears to shrink. This means that if a plank is sawn from the side of a tree trunk, the outer part will shrink more than the inner, pulling the plank into a curve. The only pranks which will not curve on seasoning are those cut right across, or towards, the heart of the tree.
The wider the planks, the worse the curve, so one usually avoids having really wide planks—above about seven in. or so. Instead, two planks are glued side by side. If you must have a single broad plank, get a well-seasoned one with a grain at the end.
Before the days of plywood the really large sheets of wood like table tops were all made up of strips of wood glued edge-to-edge. Thin, tough panels such as we now find in wardrobe sides, for example, were impossible to obtain.
Nowadays, though, we can buy really large sheets, 8 ft. long by 4 ft. wide, of plywood or blockboard. Their surfaces look like a continuous sheet of solid timber, but they are really made up of several very thin layers of wood, glued flat together.
In plywood, as many as 32 thicknesses of wood might be glued together, the grain of each sheet running at right angles to the sheet above and below it. Because of this arrangement, and the extreme thinness of each sheet, the shrinkage of one sheet is opposed by the shrinkage of the sheets above and below, so that the plywood as a whole does not warp.
For large flat surfaces, then, plywood may be used. The thinner sorts are not very stiff, so they are usually surrounded by a frame of ordinary timber, to which the ply is glued, or in which slots are cut to hold the ply edges.
Blockboard is a rather thicker material, from in. thick upwards, consisting of lengths of timber laid side by side, and sandwiched between two sheets of plywood. The whole lot is strongly glued and makes a thick, non-warping, stiff board which can, in many cases, be used without framing.
Some popular boards are made up from sawdust or chippings, glued together and rolled out in large sheets, from 4 in. thick upwards. These are hardboard or the thicker and softer chipboard. They are much the cheapest sheet materials and have hundreds of uses in the home. You can buy them already covered with sheet plastic, paint or even metal.
Finally there are many varieties of machined ‘mouldings’ which are strips of wood already shaped to various sections. The most useful of these is the double-channel tracking moulding with which you can make sliding doors for many home items easily and quickly.
To sum up:
1 Always buy fully seasoned timber from a reputable dealer who has proper storage facilities.
2 Plain timber may be hardwood or softwood; start with the softwood and graduate to hardwood later. Avoid wide. Planks if possible.
3 Plywood is made up of many thin layers of wood glued together. It is tough, reliable and easy to work but needs framing for strength and is not cheap.
4 Blockboard is strong, stiff, seldom requires framing, but is expensive.
5 Hardboard and chipboard are much cheaper, very serviceable indoors, easy to work and will last for years if not harshly treated. They usually need framing.
6 Mouldings are decorative and the channelling is very useful, but they are fairly expensive.