Checking For Faults When Buying Timber

Where timber is to be used for furniture or any other function where strength and appearance are important, it is essential the best available material is purchased. A reputable timber merchant will allow you to select wood from stock to suit your own requirements and you should always take advantage of this; never buy timber without inspecting it first — which means you should never order timber by telephone.

Man-made boards

When buying man-made boards such as plywood, blockboard, chipboard, laminboard and hardboard, check both surfaces are free from scratches and dents; pay particular attention to the corners of the board, back and front. With veneered or melamine-coated chipboard, the edges should be checked carefully since these can be easily damaged in transit. Boards which are twisted or warped should be avoided; the one exception to this is 6mm hardboard which can be flattened by soaking it with water and laying it on a flat surface. The boards should be stored on edge or completely flat; they require no special treatment before use and may be used immediately after purchase. Again the exception to this is hardboard, which should be conditioned before use to prevent buckling.

Natural timber

When purchasing softwood and hardwood, much more care is necessary. Before use, the wood must be home-seasoned to enable the moisture content to adjust to that of the surrounding air; Always buy the boards with a generous allowance for wastage on length; this is to allow the required pieces to be cut using the wood to its best advantage.

There are many flaws which can exist in natural timber. Some are completely unacceptable and affected boards should be avoided; others may be cut out, but remember to make allowances for this when calculating the amount of timber you need.

Decay

This is caused by fungal attack and may be detected by soft patches and discolouration, usually due to the board being stored in damp conditions. The only treatment for decay is to cut out the affected portion and burn it.

Checks

This term usually refers to end checks which are splits or cracks in the end of boards: they are caused by the moisture in the end of the board drying out more quickly than that in the centre. End checks may be on the surface or pass through the board; the only treatment is to cut off the faulty end.

Shakes

These are separations or splits between the annual rings of the board: the opening may vary from a hairline to 2mm and may be on the surface or right through the board. There is no effective cure for a shake and you should avoid buying any boards affected in this way.

Splits

Splits are large separations of the fibres and are the signs of physical damage to the board. Affected boards should be avoided at all costs.

Knots

A knot is where a branch left the tree and new wood has grown over. If the branch was alive when it was grown over, the result is a ‘live’ knot which will remain in the board; if the branch was dead, a ‘dead’ knot results and this will drop out in time. Knots can provide an attractive feature and are perfectly acceptable’ as long as the board is used for decorative purposes and not for strength. For example, timber with knots can be used successfully as wall cladding, but should not be used for such things as table legs.

knots-in-timber

The main problem with knots occurs when planing or otherwise working them because they tend to leave a rough or pitted surface. Loose or dead knots with black rings around them should be avoided since they will almost certainly drop out when the timber is fully seasoned. Discard any boards which have half a knot showing on an edge. Thunder shakes These are small shakes across the grain of the board and are caused by wind or storm damage tearing the fibres. Thunder shakes always weaken the board considerably and should be avoided.

Holes

Various pests attack living trees and tunnel through the wood, causing holes of 1-10mm in diameter. The holes appear mainly in hardwoods such as African walnut. The pests have long since left the boards by the time they reach the timber yard and the presence of such holes does not mean the board is infested with woodworm. There is, however, no cure for this condition; the affected area of the board must be cut out and discarded.

Resin streaks

This is a condition which affects mainly softwoods; dark brown streaks run down the annual rings and may ooze sticky resin. The resin will eventually dry up, but the brown streaks will remain. Proper home seasoning will allow any exposed streaks to discharge their resin, but will not stop discharge occurring from new streaks which may appear as the wood is worked. Excess resin clogs glasspaper instantly, rendering it useless, and will stick to the sole of a plane; allow the resin to run away before continuing work.

Bark pockets

This is a fairly rare condition caused by the tree being damaged during its growth; new wood eventually grows over the wound, but the damaged bark remains inside the tree. The faulty piece of wood must be discarded.

Waney edge

When a board has one edge with bark on it or the brown edge beneath the bark, it is called waney-edged. In a few cases this edge may be used as a decorative feature, but normally the faulty edge has to be sawn off.

Cupping

As a slash-sawn board seasons or dries out, the annual rings tend to straighten up; this gives a concave shape to a wide board. It is part of a natural process which is difficult to stop and is the main reason why narrow boards are used in preference to wide ones for making such things as table tops, since the cupping can be placed in opposite directions to cancel itself out. The fault may be cured by ripping the wide board into a series of narrow boards and planing the edges square before gluing them together again. To avoid the defect altogether, quarter sawn boards should be bought, but these are normally available only in hardwood.

Twisting

This is when a board twists in a corkscrew fashion along its length. It is sometimes possible to correct this fault by clamping the board in a position to reverse the twist; but such measures are not usually successful, so avoid affected boards.

Bowing

Caused by incorrect stacking during seasoning, this is where the board is bent or sags along its length. Bowing can be an acceptable condition, depending on the extent of the bow and the length of the board required.

There are faults which are caused by poor workmanship in the timber yard, when the timber is being worked with a rotary plane. Unfortunately these are fairly common and all affect the finished size of timber.

Incomplete planing

This is when the plane has not been adjusted to cut deep enough and saw marks are visible. To remedy this, the board must be planed thinner, normally with a hand plane.

Ripple

A ripple or wavy finish is normally the result of using a blunt or incorrectly adjusted planing machine. The board must be planed thinner with a hand plane to clean off the ripples.

Out of square

The most common timber yard fault, this is when the edges of a board are not planed square to the width. You must plane the edges square or the finished structure will be out of true.

Variable thickness

When you require a quantity of wood of the same section, always check all boards are finished to exactly the same width and thickness; PAR (planed all round) timber is planed only to nominal dimensions and all timber for one job should be obtainable from the same batch.

With radial cutting, the cuts are in-lade from the centre of the timber along the medullary rays. 4B With tangential cutting, the cuts are made across the medullary rays. 5 Stacking timber to allow air to circulate

When buying timber, therefore, have a good look at the timber merchant’s store; this will allow you to make an approximate assessment of the moisture content of the timber you are about to buy.

Storing

When the timber has been cut roughly to size (allowing plenty for wastage). it should be stored where the finished article is to be situated. Stack the planks vertically or horizontally with small pieces of waste wood between them to allow air to circulate. It will take at least two weeks for the timber to reach its equilibrium point. If these simple precautions are not taken, a project which may have taken many hours of work will shrink and distort, causing doors to stick, drawers to jam, joints to open — and many other faults.

Warning

Beware the term ‘seasoned’ timber; it means very little. Even antique furniture will shrink and warp if brought from a cool bedroom to a hot, centrally heated sitting room. Timber never loses its ability to absorb or dissipate moisture to reach equilibrium with the surrounding air.

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