How to ‘dig in’ a decent fence post

At Renovation Warehouse, we almost always have round posts and rectangular posts and sleepers available, and we update on TradeMe when square posts come in.

How to dig in a decent fence post

Getting your posts bought and lugged home is the easy part. Putting a post in perfectly is more challenging, but don’t worry: fences have been around for thousands of years, and if a caveman can put one in, so can you.

Follow this advice and you won’t have to go digging up a wonky fence and starting again.

Firstly, the tools.

  • Measuring tape
  • String / string line with chalk
  • spirit level designed for fence posts (the right angled ones with two dimensions which strap onto the post are ideal)
  • Tape measure
  • To get the cement around the base of the post, you’ll need water and a spade
  • You’ll likely need a chainsaw at the end in case you need to trim the tops off your posts to get them perfectly level.

Now, the building materials:

  • Your fence posts – a bit taller than required as you can lop the tops off with a chainsaw once they are firmly in the ground and then cap or paint the unprotected end
  • Smaller wooden stakes to help position the fence posts and keep them upright while the cement dries
  • Thin, easily removable nails – you’ll need these to secure stakes to hold the fence post upright while the concrete dries

How to dig in a decent fence post:

1. DIG DEEPLY

A fence post needs a third of its total length in the ground for stability reasons. It’s likely your post will be at least 1500mm, so you’re looking at 500mm in the ground, or 600mm for a 1.8m fence post.

If you use a post hole borer to dig the holes, you’ll have a hole which has strong sides and little dirt subsidence. The downside, though, is that post hole borers seriously make you sweat! Even petrol powered post hole borers require a lot of manpower, whether one or two person-operated.

It’s worth the effort: when your hole is deep enough to bury a sufficient portion of the post in the ground, it means you don’t have to fill it with as much concrete, meaning less unsightly concrete sticks up at grass-level and you can cover it with soil and make the concrete invisible.

2. USE THE CORRECT SIZED POST

Ensure your posts have all the same dimensions. If two posts don’t align perfectly, it’s going to be that much harder to attach the rails so that they are perpendicular.

Square posts with minimum 75 – 100mm sides give plenty of room for rails to be attached, and hinges too if you’re hanging a gate – having said that, Renovation Warehouse always has irresistible specials in store, so perhaps you can pick up a load of rectangular posts for a good price.

3. GET IT PERPENDICULAR

When a line or edge is perpendicular, it means it’s 90 degrees to a given line, plane or surface. In terms of sinking a fence post, it’s essential to have the hole deep enough to allow the post to sit in the ground perpendicular, without wobbling, while you line it up with the posts on either side of it. A string line allows you to check that your rails will sit flush against your posts with no gaps.

4. STAKE YOUR POSTS WHILE YOU PREPARE THE CONCRETE

The stakes you should have handy should be nailed into the posts while you pour the concrete in. Do the concrete only once the post is positioned perfectly, because you’ll need to check that every single edge of your posts aligns with its neighbour and that the post has been put in upright and balanced.

5. ENOUGH CONCRETE – BUT NOT TOO MUCH

Don’t completely fill the hole with wet cement, as you may like to pour the cement powder into the hole then stir water into it. Cement expands as it turns into concrete, so it’ll come rising up above the surface if you’ve poured too much dry powder into the ground.

Then again, don’t skimp on the concrete. Think about the tonne or so of wood the concrete is supporting. It takes some very strong, very deeply buried concrete to hold up a tonne.

A SPARE IDEA

One alternative to cement is Sika Post Fix, available from any hardware store. This is essentially instant, lightweight cement. You mix it in a bag and pour two bags of the stuff into the post hole. It’s the same type of hardening insulation foam used in boats and hardens like polystyrene. The stuff is incredibly strong and can hold up a post, but it lacks the heaviness of concrete.

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