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How to use a post hole digger

Date posted: 10 March 2015

Either you are putting up a bird house on a pole, erecting a flagpole or building a fence. Here, you will find a guide to help you get the holes at exactly the right spot, using the proper tools, so you enjoy a splendid outcome. 

So, if you have more than just a couple of postholes to dig, make sure your arsenal is not limited to a clamshell digger and a shovel. Instead, add a tile spade as well and a tamper-end digging bar that will get you places no other tool can.

Now, if you want to dig a small hole in diameter, the shovel won’t do the job and you will end up with holes larger than you need. In this case, you can hire a post hole digger which is ideal for use on challenging terrain and can dig holes up to 200mm in diameter in preparation for fence post installation. If you requires holes for larger posts , then you can use the hydraulic post hole auger which is capable of digging holes up to 300 mm in diameter.

Step 1: Get Posthole Diggers

A posthole digger is specially designed for this particular task and requires minimum effort on your end while getting it all done in the least time.  However, there are a few things to note before you start. 

  • It’s hard to post hole diggers in rocky soils, given that a small stone will block the digger’s cutting edge and won’t allow it to penetrate the soil.
  • Dry soils, as well as sandy and loose ones, are difficult to remove from a hole. This is because of the clamping action of the digger’s jaws that is less effective on non-cohesive materials. It is suggested to start digging holes, fill them up with water, and then come back the next day to remove the soil that will have softened by then.  
  • Hard earth (e.g. clay) is next to impossible to dig with a pair or posthole diggers.
  • The max effective depth of a posthole digger is approx. ¾ of its handle length. This means that if you have a 5-foot pair, expect to dig 3 ½ deep, more or less. 

Step 2: Select the Location

For a project that requires just one hole (e.g. install a flagpole), you can gauge by sight, but for projects where you will have to dig many holes, it’s best to plan out your holes’ locations more accurately, using a string line and stakes to get guidance, and a long measuring tape. Pick one end of the line and plant the stakes along that line. Then have the string tied to one stake -make sure it is taut- and then tie it to the other stake. 

Note: Before you do anything else, first ensure there are no utilities going underground that area you are about to dig. Upon any doubt, better call the local utility locating service to get proper help. 

Step 3: Start Digging

First, drill a pilot hole, by holding the handles of the posthole diggers (one per hand), and then pushing them into the soil. You will be able to cut a plug out of the earth, and potentially turf, if any present. In any other case (e.g. the earth resists the blade), repeat the push until you finally make it and break up the soil. 

Capture the soil in the hole digger’s jaws (between the blades) –you can do that easily if you spread the handles apart- and apply pressure to grasp the soil securely. 

Lift the posthole digger out of the hole. To get rid of the extracted soil, you should swing the hole digger to the side of the hole and just close the handles back together. 

Note: The earth should be penetrated a few inches first and then extract the dirt. A clamshell digger can help you remove the loose soil fast.

The same procedure has to be repeated, and you will go deeper with every thrust of the hole digger; just remember to make the hole wider the more you go deep, to be able to stabilise the post and always tamp the bottom of each hole to make the loose soil more compact.

In case you come across any difficult materials (e.g. roots), cut them through by rotating the blades. If this doesn’t work, wet the soil and you will see how smooth your job will be from then on. 

Alternatively, you can use a jackhammer or a spud bar (also known as digging stick), whose heavy weight will help break up small rocks, tree roots, etc. 

Step 4: Installing the Posts

Place the posts, plumb them up (you can use a spirit level) and pat down the fill material that will help stabilise the posts. 

To have a solid post, it is best to set posts in concrete or use dry sand. Some contractors dump dry concrete that is pre-bagged right into the hole, and then sprinkle with water to set fence posts in place using concrete. However, it is not a suggested technique as it dramatically reduces the concrete’s finishing strength (by up to 80%) since there is no way you can control the water proportions. For that reason, it’s best to mix concrete by using the minimal amount of water. For example, damp sand feel is sufficient to initiate the required chemical reaction and make the concrete hard. So, try to resist to make concrete the easy way and add more water, as it will have an impact on the finished strength of the concrete. 

If you are dealing with a large project, using bagged concrete is more expensive, so making your own is definitely recommended. You can do that by mixing 1 part type N or type 1 concrete with 3 parts of sharp masonry sand (or 2 parts of gravel if you want to bulk up the mix).
Now, if you don’t wish to use concrete, you can put a rock into the hole where the post will rest on, and then fill around it with gravel or rocks. Finally, pound down sand, to make sure the post will remain straight. 

What tools you will need:

  • Measuring Tape
  • Posthole Digger
  • String Line
  • Spirit Level
  • Shovel (to backfill the holes)
  • Clamshell Digger
  • Tile Spade and/or a Tamper-End Digging Bar

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