How to Replace a Gate Post

July 10, 2013 at 7:11 pm
Print Friendly, PDF & Email

There may be lots of reasons why you need to replace a gate post; they can rot off, be damaged by people, livestock or machinery, or simply sag or move with time and use. This step by step guide will walk you through how to replace a gate post. In our example, we’re replacing an 8 inch wooden gate post that is concreted in place, and surrounded by tarmac, but you can easily adapt the guide to suit your surroundings.

Estimated time to allow

3-5 hours, depending on the condition of the ground and existing gatepost.

Tools

Pencil
Tape Measure
Spirit Level
Spade / Shovel
Line / String
Post Hole Digger (optional)
Excavation tool (optional)
Breaker (optional)
Bolster Chisel
Lump Hammer
Stone Saw (optional)
Laser Level (optional)
Saw
Chainsaw (optional)
Sledgehammer
‘Tamping’ Bar (optional, for compacting concrete as you fill the hole)
Trowel / Float
Wheelbarrow
Another pair of hands (if you have a large span to work with, this will be essential at the setting out stage)

Instructions

  1.  If the damaged/rotten gatepost is still in position, you may need to remove it in order to work round it. In this case, the post was rotten at the base, so it was removed straight away. Before you remove the damaged post, make sure that you have measured the distance from the inside face of the remaining post to the inside face of the damaged post. Make a note of this measurement as you’ll need it later to make sure the replacement post is in the same place.
  2. If the post has broken above the ground, you’ll need to excavate the part which is still in the ground. In this instance, the damaged post had been set in concrete and was surrounded by tarmac so the breaker was used to break up the existing concrete and excavate the hole. You can use a variety of tools to dig the hole, depending on the condition of the ground and your preference. We used a post hole digger to remove the soil and broken concrete as we went. For an 8 inch (200mm) gatepost standing approximately 5-6 feet (1500-1800mm) above the ground, you should aim to excavate to a depth of 3 feet  (900mm).  
    TIPS: 
    •  Find the edge of the existing concrete and dig a small hole alongside, so that as you break the concrete, it has somewhere to go. Don’t make it too big though, as you’ll waste concrete at the installation stage.
  3. Depending on the setting, you may wish to tidy the edges of the hole that you’ve made at this stage, although you may find this easier once you’ve set your replacement post in the hole.
    TIPS: 
    •  As this post was set in tarmac, we used a bolster chisel and lump hammer to create a neat edge for new tarmac to be laid against. If you have one available, a stone saw used carefully would be the ideal tool to use here.
  4. Now that you have a hole at the correct depth, you need to work out exactly where to site your replacement post, as well as the height at which it will stand above the surface so that it can be cut to the correct length.

  5. String a line from the remaining post, securing it so that the line passes across one of the outer faces of the remaining post. Pull the string beyond the hole, and find a way to secure it in place so that the line is parallel with the face of your remaining post. We’ve used a horizontal road pin to allow us to adjust the position of the line so that it’s perfectly parallel with the remaining post.
  6. Next, use the measurement that you noted in step 1 to measure from the remaining post to the hole. Now that you can see where the inside face of your replacement post will fall, you will need to ensure that the hole is sufficiently wide (throughout its entire depth) that the replacement post will stand upright in the hole and still have plenty of space around it (4-6 inches, 100-150mm in all directions)  for the concrete that you will be securing it in place with. Remember the key is the depth of the hole, rather than the amount of concrete surrounding the post – the depth will give the stability.
    TIPS: 
    •  The best way to do this is mark the distance (we’ve used another horizontal road pin held in place with weights) and then offer the post up to the hole, as a ‘dry-run’. Get the post standing in the hole and level it up with a spirit level in both directions. You may need to adjust the soil in the bottom of your hole, or use shims of slate to get the pole to stand upright on its own. This will prevent gravity trying to alter its placement once you inevitably have to let it go further along the process.
  7. Lastly, you need to make sure that your replacement post is the same height as your remaining post. Measuring the height of the remaining post above the ground and using that measurement is unreliable because it assumes that the ground between the posts is even, so will often result in posts that vary in height and don’t look very professional. We’ve used a laser level (see How to Use a Laser Level) in this instance to get the height perfect, but if you don’t have a laser level handy, you can use another string line and a spirit level, as described in step 7.
    TIPS: 
    •  We’ve recommended a string line technique as an alternative to the laser level because we’re working on a full size driveway gate. If your span is smaller and can be bridged with a long level, or a shorter level and a nice straight piece of wood, this may be easier for you.
  8. String a line across from your remaining post, this time passing it over the very top of the remaining post. Making sure that your replacement post is stood up straight and in the right position, string the line across it and adjust the height of the line until it is level along its length by holding a spirit level up to it. Mark the position of the line on your replacement post. Measure the distance from your mark to the very top of the replacement post and note this measurement. Remove the post from the hole and use the measurement that you’ve just noted to measure from the bottom of the post upwards. Mark and cut the post to length. (for an 8 inch post, a chainsaw saves a lot of sweat if you are qualified to operate one). The replacement post will now be the same height above the ground as the remaining post when placed into the hole.Once your post is the right height and in the right place, you will need to secure it in place with concrete.
  9. Using ‘all in’ or ballast sand and cement, mix enough concrete to fill the hole and completely surround the base of your post, using a 4:1 ratio of ‘all in’ or ballast sand to cement and aiming for a ‘semi dry’ consistency (see How to Mix Mortar / Concrete). There is no need to add gravel or other substrates to the bottom of the hole in order to aid drainage. We’d also recommend avoiding Postcrete for a gate post of this size, but you could use this on smaller posts if you prefer.
  10. Once you have your concrete mixture ready, check again that your replacement post is standing straight in the hole and is the right height in relation to the remaining post. If you are satisfied at this stage, begin carefully surrounding the base of the replacement post with concrete, a shovel-full at a time. After you have enough concrete around the post to offer it some support, ‘tamp’ the concrete down gently and check that the post is standing straight and has not moved. 
    TIPS: 
    •  Don’t pour the concrete into the hole; it should be too dry for you to be able to do this gently, so will slop heavily into the hole and is very likely to knock your carefully placed post out of alignment.
  11. If you have to adjust the post again to get it upright, this is most easily achieved by using a long bar (such as the excavation tool) to gently tap or lever the base of the post into position. Once final adjustments have been made, tamp down any concrete which you’ve introduced into the hole and gently keep adding concrete, tamping down to compact the concrete together and expel any air as you go. Keep mixing and adding concrete until you’ve filled the hole to within 2-3 inches (50-75mm) of the edge of the hole.
    TIPS: 
    •  As soon as your post is held securely by the semi dry mix, you can start making the mixture wetter. You’ll want to get as much ‘wet’ concrete into the hole as possible.
  12. To fill the last few inches you’ll need to mix a slightly wetter (than your semi dry mix) batch of concrete. Aim to make the mixture slightly wetter, but if in doubt, err on the side of dryness as it’s easier to add moisture to the mix than take it away.
  13. Use the wetter concrete to fill the hole to the final level, which will depend on how you plan to finish off  around the base of the post. As we planned to use tarmac to match the existing surface, we left a 1.5 inch (40mm) gap to allow for cold tarmac to be placed on top of the concrete. However you plan to finish around the base of the post, use a trowel or a float to smooth the surface of the concrete, chamfering (sloping) it away from the post in all directions. You’re aiming to make a smooth, sloped surface so that any rainwater runs away from the post and is unable to pool around the base of the post, causing it to rot in the first place.
  14. Allow the concrete 6-8 hours (ideally as long as you can) to harden before attempting to fit any gate furniture, leaving at least 48 hours if your replacement post is at the ‘hinge end’ and will be bearing the weight of the gate. If you’re covering your finished concrete with tarmac or similar, make sure that it is fully hardened before attempting to work on top of it. Soil or gravel can require less disturbance, so could be placed on top of the concrete more quickly if necessary. In any scenario, we would recommend leaving the concrete to harden for as long as you can before doing anything which could disturb it.

Product Recommendation

The Titan Breaker that we used for this job really is an outstanding piece of kit, putting its significantly more expensive counterparts to shame. If you were working this breaker hard every day, it probably would give up quicker than the DeWalt or Makita equivalent, but don’t forget that you can go through 3 of these for the same price as a DeWalt or Makita. To give you some idea of the product’s lifespan, ours did 3 years of hard work (with no maintenance) before giving up. For £170, you won’t find a better breaker.