| The hundreds of different timber species, which vary | | | | known as conversion and seasoning. Some softwood |
| widely in their appearance and properties, are usually | | | | may be preservative treated. |
| classified into two broad groups hardwoods and | | | | Sawing |
| softwoods. Hardwoods come from broad-leaved | | | | Timber is generally sawn: |
| trees such as ash and oak. Softwoods come from | | | | • through-and-through (sometimes called |
| coniferous trees which mostly have needle-like leaves | | | | plain-sawn or slash-sawn). In this method the log is |
| - Norway spruce, for instance. This is a botanical | | | | cut into planks by simply slicing through the tree. |
| classification and the terms are only a general guide | | | | Most of the growth rings make an angle of less than |
| to the hardness of the woods - balsa, for example, is | | | | 45 degrees with the surface. The moisture content |
| probably the softest wood available yet it is classified | | | | of a tree is greater around the outside than at the |
| as hardwood, whereas yew, a hard wood, is | | | | centre, so when through-and-through sawn wood is |
| classified as a softwood. | | | | dried all the planks, apart from those which are cut |
| Traditionally, softwoods are cheap, easily-worked | | | | directly through the centre of the tree, have a |
| timbers used in house construction for flooring, | | | | tendency to warp. The planks have to be planed flat |
| rafters, joists, windows and doors. They are often | | | | after drying |
| painted. Hardwoods, on the other hand, are generally | | | | • quarter-sawn. Timber has growth rings at an |
| more expensive and considered to be more durable, | | | | angle of 45 degrees or more to the surface of the |
| and more difficult to work. They are used for making | | | | board. It is often more expensive than |
| furniture and sometimes finished with stain and then | | | | through-and-through sawn timber but much less likely |
| polished or varnished to bring out their natural | | | | to warp. |
| decorative features of grain and texture. | | | | Drying |
| In recent years, many of the traditional British and | | | | Timber is dried by either stacking it in the open air or |
| European hardwoods such as ash, elm and lime - | | | | by drying it in a kiln. Drying makes timber stronger, |
| have been replaced by varieties from regions of | | | | more resistant to fungi and better for painting and |
| Africa, the Far East and North and South America. | | | | varnishing. |
| The most commonly available hardwoods are the | | | | Once timber has been dried it can still gain and lose |
| so-called 'red' hardwoods (mainly mahogany) and | | | | moisture - it shrinks as it loses moisture and expands |
| yellow-coloured ramin, but there is a wide range | | | | as it gains moisture. Timber which has been stored in |
| available through timber merchants. | | | | the open will shrink when brought indoors, particularly |
| Because of the high cost of hardwood, it has largely | | | | into a centrally heated room. The effect this has on |
| been supplanted in do-it-yourself work by man-made | | | | the timber depends on how the timber was sawn - |
| boards covered with a thin veneer of hardwood | | | | through-and-through sawn timber tends to warp |
| (teak or mahogany, for example) widely used in | | | | whereas quarter-sawn timber tends to shrink evenly. |
| furniture making and shelving. | | | | Whenever timber is moved between environments |
| There is a good selection of man-made boards | | | | which are likely to have very different humidities, it is |
| available as a substitute for using plain boards of | | | | important to allow time for the timber to come to |
| timber: there is also a wide choice of both hardwood | | | | equilibrium with its new surroundings. This may be as |
| and softwood mouldings for use in the home. The | | | | little as a few days for small sizes but well over a |
| more common sizes of softwood and some types of | | | | week for larger ones. |
| hardwood are available in the large do-it-yourself | | | | Preservative treatment |
| superstores as well as some do-it-yourself shops; for | | | | Some timber is available pre-treated with |
| the full range, go to a timber merchant. | | | | preservative. This has had the preservative pressure |
| Conversion and seasoning | | | | impregnated and will lengthen the life of timber used |
| A tree which has just been felled contains a lot of | | | | outside and also in structural work. Cut ends should |
| moisture. To make it into timber which can be used, | | | | be additionally treated. |
| it has to be sawn and dried. These processes are | | | | |