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Property: Behind every good shelf there's a plastic plug

Jeff Howell pays homage to the small gadgets which enable DIYers to boast that they haven't got a screw loose

REGULAR readers of this column will know I am not enam-oured of most modern building materials. They can create more problems than they solve and are usually marketed to make a profit for the manufacturers, rather than to improve the quality of the nation's housing stock.

But there is one group of materials that save so much time, and seem to offer such advantages in performance, that it is hard to imagine how we ever got along without them. I am talking about those plastic plugs used for fixing screws in walls.

We have become so accustomed to the convenience of these little gadgets that it is astonishing to think they first appeared as recently as the 1960s.

Before that, most fixings were made by nailing into timber blocks set into the brickwork. Bricklayers used to build these blocks in at intervals around buildings, especially up the sides of door and window openings, for securing the frames. They provided a good fixing for nails, but over time the timber may have dried out and shrunk, allowing the blocks to work loose.

And when builders wanted to nail or screw something to a wall in a place where there were no wood blocks, they had to drill a hole and plug it by hammering in a suitable piece of timber.

The first proprietary fixing systems appeared in the 1950s, consisting of wood pulp or fibre plugs. The plastic plug was not far behind. Plastic plugs belong to a group of fixings called expanding mechanical anchors, which means that as you turn your screw into them, part of the fixing is pushed out sideways to grip the sides of the hole by friction. The big boys of the species have 25mm bolts pushing serrated stainless steel wings out into reinforced concrete - they can hold loads of several tons.

But for putting up a few shelves at home, the small plastic variety are all you need - as long as you understand a couple of basic principles. First, the drilled hole must be exactly the right size for the plug and the screw; the drill size will be marked on the packet or the fixing itself. If the hole is too big, the plug will rotate within it and you will never get the screw to bite. If the hole is too small, there will not be enough room for the screw and you will only get it halfway in before it breaks off, or you give up from exhaustion. Most DIYers have a packet of assorted masonry drill bits, but these are often too short. Buy some good-quality long masonry bits - 120mm or so. The most useful diameters for plastic plugs are 6mm, 6.5mm and 7mm.

Second, when fixing shelves or skirting boards to a wall, don't try to fix to the plaster. The plug needs to tapped through into the brickwork. The way to do this is to put the screw against the mouth of the plug, and tap it into the drilled hole with a hammer until it feels firm. Then, and only then, start turning with a screwdriver.

q Jeff@doctoronthehouse.demon.co.uk

q In a recent Doctor on the House column, it was suggested that a British Wood Preserving and Damp-proofing Association code of practice advised against ceramic tube damp proofing.This reference was inserted in error in the course of editing. The BWPDA code does not mention ceramic tubes.