The number of bags of Postcrete you need per fence post depends on several factors, including the size of the post, the diameter and depth of the hole, and the type of fence post being installed. In general, you’ll need two 20 kg bags of Postcrete to set a 1800 x 75cm x 75mm (6′ x 3″ x 3″) fence post in a hole that’s 3 times the size of the post (225mm in diameter) and 1/3 to the height of the post (600mm deep).
Postcrete is a type of ready mix concrete made specifically for fence posts. It is pre-mixed concrete made from mixing of cement, sand, aggregate and additives that help it secure wood, concrete, and metal posts to the ground. It sets extremely quickly and allows landscapers to efficiently fix posts to the ground.
Postcrete is specially designed for fixing of fencing, decking, and gate posts to the ground. This is typically used by landscappers as it only need to add water before it begins to work. It should not be used for shed base and foundation due to less strength.
It takes 5 to 10 minutes for Postcrete to set. However, it will continue to get harden and gain strength over the next 10 to 12 hours. After 24 hours it is fully set. To determine how many bags of Postcrete you need per post, remember, as a general rule of thumb, you’ll typically need two 20 kg bags of Postcrete for a 75mm x 75mm (3″x3″) fence post.
How much Postcrete do I need per post? Generally, this will vary depending on the size of your post and depth and width of hole, however in general, you will need at least one 20kg bags of Postcrete per (100 x 100mm) post. However, landscappers in the industry often suggest to use two 20kg bags per fence post.
The general rule of thumb, the depth of the post’s hole needs to be buried 1/3 to 1/2 of the actual above-ground height of the post. So, 1800mm high fence posts ideally need to be buried 600mm into the ground. The diameter of your post hole need to be 3 times the diameter of your post. So, if you’re using a 100×100 mm square post, your fence post hole will ought to be 300mm in diameter, while for a 75×75 mm post, post hole will need to be 225mm in diameter.
In general, if the fence post size is 2400 x 75 x 75 mm, your post hole should be 800mm deep and 225mm wide, while for a 2400 x 100 x 100 mm fence post, your post hole should be 800mm deep and 300mm wide.
Likewise, for a 3000 x 75 x 75mm fence post, your post hole should be 1000mm deep and 225mm wide, while for a 3000 x 100 x 100mm fence post, your post hole should be 1000mm deep and 300mm wide.
In addition, for a 1800 x 75 x 75mm fence post, your post hole should be 600mm deep and 225mm wide, while for a 1800 x 100 x 100mm fence post, your post hole should be 600mm deep and 300mm wide.
How many bags of Postcrete do i need per post
To calculate the number of bags of Postcrete needed for a fence post, you’ll first need to determine the volume of concrete required. Here’s a simple guide:
- Select size of fence post and hole: Lets for a 1800 x 75 x 75mm fence post, hole should be 225mm in diameter and 600mm deep.
- Calculate the Volume of the hole: Use the formula for cylinder concrete, volume = (3.14× 0.225m × 0.225m)/4 × 0.6m = 0.024m3
- Calculate volume of post: Lets a fence post measures 75 x 75 x 600mm in ground, so volume = 0.075m × 0.075m × 0.6m = 0.0034m3
- Subtracting the volume of the post from the volume of the hole gives you the amount of concrete required to fill the fence post hole, such as 0.024m2 _ 0.0034m3 = 0.02m3
- Select bag size & find Bag Coverage: A 20kg bag of Postcrete yields volume about 0.01m3,
- Divide: Divide the total volume of concrete needed by the coverage per bag to get the number of Postcrete bags required. Here’s the formula: Number of bags = Volume of concrete needed/Coverage per bag, so 0.02/0.01 = 2 bags.
In general, for a rough estimate, you’ll need two 20kg bags of Postcrete per 1800 x 75 x 75mm (6′ x 3″ x 3″) size fence post, while for 1800 x 100 x 100mm (6′ x 4″ x 4″) size fence post, you’ll need four 20kg bags of Postcrete.
Likewise, you’ll need 4 20kg bags of Postcrete per 3000 x 75 x 75mm (10′ x 3″ x 3″) size fence post, while for 3000 x 100 x 100mm (10′ x 4″ x 4″) size fence post, you’ll need 6 20kg bags of Postcrete.
In addition, you’ll need 3 20kg bags of Postcrete per 2400 x 75 x 75mm (8′ x 3″ x 3″) size fence post, while for 2400 x 100 x 100mm (8′ x 4″ x 4″) size fence post, you’ll need 5 20kg bags of Postcrete.
How much does a bag of Postcrete cover? Generally, 1 bag of 20kg of Postcrete yields volume about 0.01m3 and usually cover a square post with dimensions of 10 cm (4”) with a hole 20 cm (8”) wide x 50 cm (20”) deep.
How much water do i need per 20kg bag of Postcrete? Generally, you’ll need 2.5 litres of water per 20kg bag of Postcrete. The hole should be pre-soaked to limit the absorption of water from the Post Set Concrete mix.
You’ve determined the size of the hole you’ll need, you can use the chart below to determine how many 20kg bags of Postcrete you’ll need per fence post:-
| POST SIZE (in mm) | DEPTH OF HOLE | DIAMETER OF HOLE | 20kg bags of Postcrete per post |
| 3000 x 75 x 75 | 1000mm | 225mm | 4 bags |
| 3000 x 100 x 100 | 1000mm | 300mm | 6 bags |
| 2400 x 75 x 75 | 800mm | 225mm | 3 bags |
| 2400 x 100 x 100 | 800mm | 300mm | 5 bags |
| 1800 x 75 x 75 | 600mm | 225mm | 2 bags |
| 1800 x 100 x 100 | 600mm | 300mm | 4 bags |
Conclusions:
Naturally, you’ll need two 20 kg bags of Postcrete per fence post, so two 20kg bags of Postcrete are enough to set a fence post measuring 1800mm x 75mm x 75mm (6′ x 3″ x 3″) into a hole that’s measuring 225mm in diameter and 600mm deep.