Types of Wall Fixing
Though largely superseded by more modern methods, the traditional hand-shaped wood plug can be useful where nail fixings have to be made. If the plugs are left proud of the brickwork they can be cut to any desired length where the brickwork is being lined or clad. Plugs should be cut with a gentle taper so that they have a tendency to twist and grip. Sharp tapers do not fill the recess and, as wood tends to shrink, become loose. Plugs should be a tight fit in the hole.
Plugs into external walls or in situations where dampness is likely should be treated with a preservative before being driven in.
Iffixings are to be made, hard-wood plugs should be used and, once inserted, a pilot hole, of slightly smaller diameter than the , should be drilled. Brass or bronze should be greased with wax or tallow before being driven home.
These are made in various materials, ranging from fibre, soft metal and synthetic resin. They require only a neat, round hole, matched to the size of the plug and a little larger than the screw to be used.
It is important that hole, plug and screws should match in size. The holding power of the plug depends upon the frictional grip obtained when the screw expands the plug.
If a small screw is used in too large a plug, the expansion will be insufficient to obtain a reliable fixing. A large screw in a small plug will be difficult to turn and may jam.
The composition of fibre and soft metal grips the hole and provides a firm fixing. Nylon plugs have teeth or ridges which grip the surrounding surface and stop the plug from turning.
Fibre plug sizes for any screw should be of the same length or slightly longer than the length of the thread, excluding the screw shank, which should never enter the plug. Fibre plug sizes’ are numbered to correspond with the size of screw and the drill or hole-making device used.
Sometimes, particularly in mortar or soft brickwork, a hole may become larger than desired-or a previous hole may be too large for the screw to be used. Plastic compounds, based on fibre and cement, provide an effective and reliable fixing. However, avoid making any extra-large holes; reposition the fixing in that case. The compound is wetted with clean water, formed into a plug of the required size, and rammed into the hole; usually a tool is provided for this.
If the sides are parallel, the fixing should be secure. If the hole is wider at the face than at the back, the plug may draw out. It is then better to enlarge the hole at the back to produce a ‘dovetail’ shape. The tool supplied with plastic compounds is pointed at one end to form a pilot hole in the soft compound to start the screw.
The screw should be tightened into the moist, but where a large mass of com-pound is used, the final tightening should be left until the plug has hardened. These compounds should not be used in conditions where dampness exists.
Toggles are used for fixing in hollow walls.
Gravity toggles: These have atoggle which drops vertically when inserted through a pre-made hole in a hollow wall; used with bolts for heavier fixing.
Spring toggles: These have two spring-loaded gripping arms which expand after the toggle is pushed through a hole; used with bolts for heavier fixing.
Nylon toggles: Fasteners with a slotted collar which slips over a nylon strip attached to the toggle; used for screw fixing.
Collapsible anchors: These remain in place if the screw is removed. Insertion of the screw draws metal gripping shoulders against the inner wall of the fitting.
Rubber-sleeved anchors: Used for fixing plastic or metal sheet. These can be used in solid walls. The bolt compresses a rubber sleeve against the surface of the wall.
Nylon or plastic anchors: The action of tightening the screw draws the anchor to the wall.
Nuts and bolts
Machine bolts are used for certain fixing jobs, such as wooden framing for workbenches or light construction. These usually have square or hexagon-shaped heads.
Coach bolts are used for a variety of light or heavy applications. These have rounded heads with square collar locks to prevent the nut from turning while being tightened.
Machine screws are used for small wood-working projects or metalwork. These have countersunk round, pan or cheese heads.
Rag bolts or foundation bolts are used for general construction where framework is built on to concrete foundations. The ragged ends hold firmly in concrete, leaving the shank and thread exposed.
Masonry or anchor bolts are used for fixing to breeze or aggregate blocks, brickwork or concrete. With these a plastic anchor expands to grip the sides of holes in solid walls.
These are used for jobs such as fixing shelving, battens, picture rails, skirting boards and studs for wall panelling. They are tempered to avoid bending and can be nailed straight in with a heavy hammer.
Masonry nails are in two types-one with a straight and the other a twisted shank. The latter improves penetration into hard materials.
These nails grip by compacting finely crushed material around themselves as they penetrate. This builds up a strong friction which exerts a tight grip on the nail.
The nails are made in three grades-standard, a medium and a heavy-duty pin. Standard pins are from 28mm to 70mm and will fix battens, shelving brackets and peg-board to ordinary brick or low-density concrete, aggregate or similar walls. Medium pins range in size from 22mm to 86mm and are used for fixing into harder surfaces. Heavy-duty pins are sized from 38mm to 89mm and have spirally twisted shanks.
10. November 2011 by admin
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