Tensioning Straining Wire

Mesh on its own has no shape. It is a soft net. The straining wire turns it into a fence: it holds the mesh at the top, in the middle and at the bottom, and passes the weight of the mesh and the force of the wind on to the posts. A typical garden fence around a house usually has three lines of wire. A lower fence often manages with two.

End posts, corner posts and gate posts carry most of the load. The whole tension of the wire pulls on them, so they get struts that brace them against the direction of pull. Intermediate posts only guide the wire and keep it at the right height.

Straining wire is used on mesh fences around gardens and plots, on animal enclosures, on deer fencing around orchards and on temporary fencing. Barbed wire on the angled extension arms of security fences is tensioned in a similar way.

A good tradesperson starts by checking the posts, not the wire. A loose or leaning post will only lean further once the wire is under tension.

1. Check that the posts are in line, the same height and firmly set, and that the concrete has cured enough.
2. Fit struts to the end and corner posts on the side the wire pulls from.
3. Tie the wire to the first end or corner post so the fixing can take the full tension.
4. Run the wire through the clips or holes on the intermediate posts, straight and without kinks.
5. Fit a tensioner at the next end post and tighten the wire with it gradually.
6. While tightening, watch that the wire is not slipping and that the end post is not being pulled over.
7. Tension all lines of wire evenly so the mesh is not pulled unevenly.
8. Cut off the surplus wire and bend the ends back so nobody gets hurt.

On a fence with corners, the wire is tensioned one straight run at a time, from corner to corner. A long wire pulled round several corners is hard to tension and wears through at the bends.

• Galvanised wire suits normal conditions and goes with galvanised mesh
• Plastic-coated wire has a zinc layer under the coating, copes better with damp and matches green or anthracite mesh
• Tensioners let you tighten the wire gradually and re-tighten it later; a good tensioner does not loosen by itself
• A tension bar is threaded through the edge of the mesh at end posts and spreads the pull over the full height
• Struts, brackets and clips should come from the same system as the posts so they fit together
• Tie wire is used to fix the mesh to the straining wires

For tools you need combination pliers, side cutters, the key or handle for the tensioners, and a string line or spirit level to check heights. Wire and fittings should ideally come from the same manufacturer, or at least have the same finish. A plain galvanised clip on plastic-coated wire often starts to rust sooner.

The simplest case is a straight fence on level ground with firmly concreted posts and system struts. Tensioning goes quickly and the result is straight.

The job takes longer and gets harder with:

• A slope or uneven ground, where the wire has to follow the ground and the height must be checked at every post
• Lots of corners, changes of direction and gates, because each run is tensioned separately
• Old posts that first need straightening, extra concrete or added struts
• An overgrown plot or a fence right next to a neighbour's building, with little room to work
• Removing old, rusty wire before the new wire goes up

In practice the most common problem is over-tightening. It feels as if tighter must be better. But wire that is too tight bends the end post, pulls it out of its concrete or snaps in frost when the metal contracts.

• Wire left too slack, so the mesh ripples and sags
• Missing or weak struts on end and corner posts
• Tensioning before the concrete under the posts has cured enough
• Lines of wire at different tensions, so the mesh is straight at the top and bulges at the bottom
• Wire kinked at corners, which then breaks at the bend
• Cheap tensioners that slacken after the first winter

Why do heat and frost matter? Steel stretches slightly in summer and shrinks in winter. Wire pulled as tight as possible on a hot day is overloaded by January. It makes sense to tension in mild weather and leave a little in reserve.

You can tension the wire yourself if the posts are already firmly set and the fence is no taller than a normal garden fence. Wear sturdy gloves and safety glasses, because a tensioned wire can whip back if it snaps.

1. Walk the fence and check every post is firm and upright.
2. Fit struts to the end and corner posts if they are not there yet.
3. Run a string line at the required height and mark the height of each line of wire on the posts.
4. Tie the wire to the first end post with a secure loop.
5. Thread the wire through the clips on the intermediate posts along the whole run.
6. Fit a tensioner at the other end, catch the wire and tighten it a little at a time.
7. Stop tightening when the wire is straight and pushes back firmly when pressed by hand, but does not ring like a guitar string.
8. Tension the other lines of wire in the same way.
9. Cut off the surplus wire and bend the ends back safely.
10. Check the wire again after a few days and tighten gently if needed.

If the end post moves while you are tensioning, stop. Release the tension and strengthen the post first.

• The wire looks straight when you sight along the fence, with no sags or waves
• All lines of wire are at roughly the same tension
• The wire runs at the same height at every post and follows the ground on a slope
• End and corner posts are upright and have struts fitted
• Tensioners are tight, do not slip and still have room for later adjustment
• Fixings on the posts are secure and the wire is not kinked at corners
• Wire ends are cut off and bent back
• The coating on the wire and fittings was not damaged during installation