How many bags of Postcrete per post?

For a standard 100mm (4-inch) fence post in a hole 300mm wide and 600mm deep, you will typically need two 20kg bags of Postcrete. For smaller 75mm posts or shallower holes, 1.5 bags may be sufficient.

Do you pour the water or the powder first?

Most manufacturers recommend pouring the water into the hole first (filling about one-third of the depth) and then adding the Postcrete powder. This ensures the water is absorbed evenly throughout the mix and prevents dry spots at the bottom.

How fast does Postcrete set?

Postcrete is rapid-setting and usually starts to harden within 5 to 10 minutes. You can usually release the post after 20 minutes, though it takes about 24 hours to reach full structural strength.

Can I use Postcrete for gate posts?

Gate posts experience much higher stress than standard fence posts due to the weight of the gate. We recommend using at least 3 bags of Postcrete per gate post and ensuring the hole is deeper (750mm+) for extra stability.

How many bags of Postcrete per post?

For a standard 100mm (4-inch) fence post in a hole 300mm wide and 600mm deep, you will typically need two 20kg bags of Postcrete. For smaller 75mm posts or shallower holes, 1.5 bags may be sufficient.

Do you pour the water or the powder first?

Most manufacturers recommend pouring the water into the hole first (filling about one-third of the depth) and then adding the Postcrete powder. This ensures the water is absorbed evenly throughout the mix and prevents dry spots at the bottom.

How fast does Postcrete set?

Postcrete is rapid-setting and usually starts to harden within 5 to 10 minutes. You can usually release the post after 20 minutes, though it takes about 24 hours to reach full structural strength.

Can I use Postcrete for gate posts?

Gate posts experience much higher stress than standard fence posts due to the weight of the gate. We recommend using at least 3 bags of Postcrete per gate post and ensuring the hole is deeper (750mm+) for extra stability.

Post Mix Calculator

Calculate rapid-set concrete bags for your fence.

Number of Posts

Post Size (mm)

Hole Depth (mm)

Postcrete Order

Postcrete Tip: You don't need to mix Postcrete in a bucket. Fill the hole one-third with clean water, pour in the powder, and tamp it down with a stick to ensure no air bubbles are trapped. The chemical reaction happens in the hole!

Solid Ground: The Postcrete Guide

Rapid Stability

The secret to a long-lasting fence isn't just the quality of the wood; it's the stability of the posts. Postcrete is a specialized, pre-mixed concrete that sets in minutes, eliminating the need for complex mixing or long waiting times.

Our **Postcrete calculator** helps you estimate exactly how many 20kg bags to buy based on the volume of the holes you are digging, preventing wasted material or mid-project trips to the builders' merchant.

Standard Requirements

100mm Post (600mm Deep)2 Bags (20kg)

75mm Post (450mm Deep)1 Bag (20kg)

Gate Post (750mm Deep)3 Bags (20kg)

The 3x Rule

For maximum stability, the width of your hole should be at least **three times the width of the post**. If you are using a 100mm post, your hole should be 300mm wide.

The depth of the hole should be roughly **one-third of the total length of the post**. For a 6ft fence (requiring an 8ft post), the hole must be 2ft (600mm) deep. If the hole is too narrow or shallow, the fence will eventually lean or blow over in high winds.

Drainage

To prevent the bottom of the wooden post from rotting in the concrete, add a few inches of gravel to the bottom of the hole before placing the post. This allows water to drain away from the wood.

Bracing

Because Postcrete sets so fast, you must have your spirit level and braces ready. Once the powder meets the water, you only have about 2-3 minutes to make fine adjustments before it becomes unmovable.

Pro Tip: Slope the Top

When finishing the top of the concrete, use a trowel to slope it away from the post. This ensures that rainwater runs off into the soil rather than pooling against the wooden post and causing rot at the most vulnerable point.

Postcrete & Concrete FAQ

Project Disclaimer

Always wear gloves and a mask when handling Postcrete powder, as it contains cement which can cause skin irritation and is harmful if inhaled. Avoid using Postcrete in freezing conditions as it can affect the curing process and final strength.