Strainer posts are used at the beginning and end of the fence. They hold the strain of the fence wires and support any gates. Because of the strain from the wires, a strainer post needs a ‘stay’ to stop it being pulled over. With an angle stay, this acts as a lever and creates a lifting force on the strainer, so a ‘foot’ is then needed to stop the strainer post lifting upwards as well.
First of all, your strainer post needs to be suitable for the type of fence you are building. For this example we will assume a 7-9 wire post and batten fence. The strainer should be as straight as possible and 2.4m long, with 200mm SED (small end diameter).
The fence will be 1200mm high, so your post should be half in the ground. Your hole has to be wide enough so that the foot will fit right down to the bottom and another peg across the back of the post (on top of the foot). Place the strainer at a slight angle backwards - a layback of 20mm is usually sufficient. This is in case it moves when the wires are first strained up.
The foot does two jobs – it stops the post from lifting against the lever action of the stay, and stops the strainer twisting against the force from the wires being tied off on one side.
Foot size can vary depending on ground conditions and type of fence. Generally in softer ground, a larger foot is required. Use one foot each side of the strainer with another block of wood across the back of the post is added for extra support.
A foot needs to be H4-treated (to prevent rotting) or made of a native hardwood such as Totara. The foot should be slightly longer than the width of the hole with one end pointed. Attach a length of wire, which MUST be 4mm (no.8) or 3.15 heavily galvanised stainless steel wire at least 1.8m long. Thinner wires will corrode and snap, making the foot ineffective. (See diagram left)
Sit the strainer post hard against the front face of the hole. Slide a foot down the side of the hole, pointed end first. Using one staple, attach the wire to the post on the opposite side of foot just above ground level. Hammer it firm, but not right in, just so that it holds the tension of the wire. Then ram the straight edge end of the foot down so that it is sitting against on the bottom of the hole. Repeat the process on the opposite side of the post.
Once both pegs have been put in, ram in some dirt up to the level of the top of the foot, and then place a block of wood across the back of the hole. It works best if this block is a few inches longer than the width of the hole, so that it has to be rammed home. This makes everything in the hole nice and tight (see diagram right).
Once that is done, you need to finish attaching the wire at the top of the hole. Ram the first staple home, then bend the wire backwards down towards the ground, and hammer home another staple over the parallel wire, then bend it back upwards once again, and hammer home a third staple (see diagram right).
Now that the strainer post is in, fill in the hole, ramming the dirt firm and tight as you go.
The stay - A stay is used to support the strainer against the strain of the wires. It is recommended that the stay is the SAME length as the strainer post so in this case 2.4m. A short stay would increase the leverage on the strainer post. The stay will lie alongside the wires.
First of all, before doing anything mark on the strainer post the height of all the wires, this is very important. Next the end of the stay needs to be shaped. One end needs to be ‘squared’. The edge then needs to be cut on a slight angle, and the top cut at right angles to that (see diagram left).
You then need to mortice out the strainer post to fit the end of the stay. The object is to get the stay sitting flat against the strainer, and unable to move in any direction.
To get your mortice right, rest the stay end up against the strainer where you want the stay to be. The topside of the stay should be at the middle of the strainer but can be moved either up or down slightly to avoid where the wires will be. Check with your markings you originally made on the post.
Pencil around the stay and then remove it. Use a chisel to mortice this out. It needs to be about 20mm deep. NEVER EVER use a chainsaw. There is a high chance of injury, and makes a messy job. Your stay should sit in the mortice nice and snug, however it is better if there is a bit of play and the stay is sitting against the strainer, than the mortice being too small and the stay not fitting all the way in (see diagram right.)
The stay block gives the stay extra surface area where it comes into contact with ground. If the stay block is inadequate, the strainer will move. A half length of a half round post is ideal, and sufficient in most situations. In really soft ground, a larger stay block should be used.
Place the stay back in its mortice, and position it where it needs to be, alongside where the wires will be. Mark out where the stay block is then going to sit. It should sit horizontally, with the stay in the middle. Dig out the length of the stay block, with the flat side matching the angle of the end of the stay when in place. The stay block needs to be deep enough to be on hard, firm ground. The stay should fit about halfway across the block diameter (see diagrams below).
You then need to dig a sloping trench back toward the strainer. This is where the stay first enters the ground. Place the stay back into its mortice, and then using a spade you should be able to slide the end of the stay onto the stay block. It will be tight, and you may need to use your rammer to get enough force (see photo below).
Your strainer assembly is now ready, and you can run out your guide wires...which I'll cover in the next article.
Tips and rules:
The stay block MUST be on firm undisturbed ground. If you accidentally dig too far backwards, ramming the earth back in won’t work. Use another piece of wood instead, cut it into a wedge shape, and ram it in behind the stay block. This wedge must be the same size as the stay block.
When ramming the earth around the strainer post, keep checking that it is in the right place. If it starts to move to one side, DO NOT push the post to correct it. Keep ramming the earth on the side of the lean first, and it should slowly correct itself.
For a nice clean job, use a plane or rasp to finish off the shaped end of the stay.
Most importantly, it is hard work. Unless you are very fit, or have help, you will get tired. Give yourself plenty of time so that you are not rushed. If you do get tired, stop for a break. Fencing when tired or fatigued results in a rushed, poor job which looks terrible and is prone to failure. Many fencers have had accidents when using a chainsaw on shaping stays, from being tired, fatigued, and rushed.