Property: Know your nails, or I'll insist on a tusked tenon

DOCTOR ON THE HOUSE; There's more to joining timber than hammering in a brad here, a spike there and pins everywhere, says Jeff Howell

ANY FOOL can hammer a nail into a bit of wood, which is a shame, because according to Mike the Chingford Chippy, nailing timber - rather than using proper joints - has taken much of the skill out of the noble art of joinery. After all, the title "joiner" originally referred to one who used the traditional joining methods - dovetails, scarf joints, tusked tenons - rather than just bashing in a couple of nails.

These joints are nice to look at and are the best way of building with timber, because they provide tensile strength and allow the two joined pieces to move as one. Medieval timber walls and roofs didn't use nails, and the surviving examples are a testament to the skill of their carpenters.

Another reason why nails were rare was that they were expensive, each one being hand-made by a blacksmith.

Mechanisation has now made nails available in quantities and at prices that would have astonished builders in the early 1800s, and the quality of modern timber work is almost certainly poorer as a result.

Still, if you are going to use nails, then you might at least use the right ones for the job, and every builders' merchant sells a bewildering variety. The longest nails - over 130 mm - are called spikes; the smallest are called pins. In between come brads and tacks. Got all that? I'll be asking questions later.

Cut nails are square in cross-section and are made by being sheared from steel plate. Because they are wedge shaped, these cut nails provide a good firm fixing, which is why they are also called clasp nails in some parts of the country.

There is a specific version of cut nail for fixing floor boards, called a floor brad. The "brad" bit comes from their intermediate length - 60 mm - and the "floor" bit is because their heads only stick out on one side, causing less damage to the surface of the timber. The advantage of floor brads is that when you have to lift the floor - to get at the plumbing, say - the nail comes out clean with the board, and can be hammered back into the same hole afterwards; whereas wire nails will always stick in the joist and the head will rip through the board.

Wire nails come in two types, round and oval. Round wire nails are the cheapest; they have big heads and so are useful for holding things together in structural work, but they can split the wood unless it is pre-drilled. Ovals are more expensive but are better for avoiding splits, especially for fine finishing work like skirting boards and architraves; also, their smaller heads can be easily countersunk and filled over - vital for decorating.

Nailing is a means of fixing one thing to another, and the rule is that the nail should be at least twice as long as the first thing - if you get my drift. (If you don't, think about it this way: if you're nailing a floorboard to a joist, the nail should be twice as deep as the floorboard.)

Another rule is that nails should not be driven closer together than half their length; nor should they be closer to an edge than one-quarter of their length.

Got all that? Come to think of it, it may be easier to tell you how to make a tusked tenon.

q You can contact Jeff Howell at the `Independent on Sunday' or by e-mail at: Jeff@doctoronthehouse. demon.co.uk.