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Welcome to the Bunnings Workshop community @macdonald. It's wonderful to have you join us, and many thanks for your question about building a Besser block retaining wall.
You need to start by excavating and levelling off an area for your footing, which should be around twice the width of the concrete block. You need to dig down the height of your Besser block. You'll then add about 150mm of road base and compact that down to 130mm. You can now mix up your concrete and pour your foundation. Use a trowel and spirit level to get a smooth and level surface. You should find this guide useful: How to pour a concrete slab. I'd recommend you create a foundation 100mm thick.
Once the concrete is dry, you're ready to lay your first block. Add a mortar bed and place the first block onto the foundation. The first course will be buried half of its depth into the soil. This keys it into the ground and ensures it is structurally sound.
To join the Besser blocks, you'll use premixed mortar.
You'd might need reinforcement rods on your wall. It would be best to check with your local council to find out if there are any codes specific to your location. You'd generally insert rebar into the footing when pouring it. You'd space the bar every third block. As you move up your courses, fill the cavity containing the rebar.
It would be good to install a drainage line behind the wall to redirect any water trapped by it. Weeper holes in the wall can also assist.
Please let me know if you have any questions.
Mitchell
Keep us updated on your project @macdonald and reach out if you need further assistance. We're here to help.
Mitchell
