How to build a base for retaining wall?

I have a ambitious goal to change this part of the yard into a separate entertainment area.

The pit with gravel is the drainage channel and where I am going to place a Besser block wall along.

So the first step is to determine the height and design of the wall which will be determine by a mockup.

and create a design like this

Grey-Block-Rendered-Finish-Raidsed-Garden-Bed-and-Built-In-Seat-562x350.jpg

My first step to creating this starts with the base for the blocks and I understand the base must be square and level otherwise the finished wall will be uneven.

I would like some advise on the type of base and thickness I should start with, like a compacted crushed pebble with a piping frame sitting on top to run along the pit for leveling and the thickness of concrete base on top.

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Comments

MitchellMc

Hi @Kvic,

Adding a concrete foundation under the wall would be a good idea to ensure it doesn't subside and shift over time. Depending on the height of the wall and the nature of the ground beneath, you might be able to compact it and then add crushed rock and compact it again. We hire compactors that will make your life easier. You really want to thoroughly go over the area to ensure the ground is compacted.

Besser Block retaining walls are mortared together. The blocks need to be core-filled with grout and reinforced with steel for engineered and load-bearing walls. It's best to check with your local council to determine whether your wall requires engineering.

Having the wall on top of the existing crushed rock and drainage likely wouldn't be a good option as it will prevent surface water from falling down into your Agi-line. I would suggest building the wall on the lower side of the slope to the drainage line so the water flows down, hits the wall, and then falls into the drainage.

Whether you're constructing a concrete foundation or laying crushed rock foundation, you'd have those around 100-150mm in depth. Here's a helpful step-by-step guide: How to pour a concrete slab.

Please let me know if you have any questions.

Mitchell

Kvic

https://www.workshop.bunnings.com.au/discussion/comment/28109#Comment_28109

Hi Mitchell

The wall will be free standing and I feel the height will be cap around 6 blocks above ground with drainage running along both walls.

I sat on a wall with a height of 2.5 - 3 blocks and the knees and hip was inline and comfortable

Not going to disturb the surrounding area and place the first layer below ground as the compactor is 420mm wide and 68 kg I will have one end of the ditch at ground height as the ground level is lower that the picture above so the wall will rapidly decline.

Will need Steel reinforcement to be placed in the concrete, does Bunnings have them?

Step 1. Dig trench 500mm wide by 650 mm

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/76625#Comment_76625

Will the wall be six blocks high, and will it retain any soil @Kvic? Either way, you'll likely need to speak with your local council to see if engineering and approval with be required. A Besser block wall that high is a sizable structure and, if it's not designed and constructed correctly, could cause significant damage if it were to collapse. You're also building it on a slope which adds to the complexities.

A six-block high wall would require reo bars inserted into it for stability.

Mitchell

johnnymac

https://www.workshop.bunnings.com.au/discussion/comment/102277#Comment_102277

Hi Mitchell, I am also wanting to build a small block wall only mine is only 1 row high (190mm) but will have soil behind it. My question is whether I should have a concrete footing (or just compacted cracker) and Reo bars in such a small wall? I am thinking as the blocks are mortared together then a concrete footing is better or if I concrete fill them they can simply be butted together as the face will be rendered?

It will have a 190x45 mm H3 Pine capping (see photo)

PXL_20250222_215423570~2.jpg

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/121671#Comment_121671

Hi @johnnymac,

A warm welcome to the Bunnings Workshop community and thank you for your question.

With a single row of blocks, it won't be retaining any considerable weight, so there's no real need for a concrete footing that is tied into the blocks.

You can just dig out a trench around 100mm deep, add cracker dust or drainage gravel and compact it with a tamper.

You can then mortar your blocks in place and core fill them with more cracker dust or gravel.

If the wall needed to retain a lot of soil, you would need to adjust your approach, but a single row doesn't need more than the above.

Let me know if you have any further questions.

Jacob

johnnymac

https://www.workshop.bunnings.com.au/discussion/comment/129831#Comment_129831

Thanks Jacob that's easier than I expected and much cheaper. One other question is do I need and horizontal Reo rod between the blocks and if so doesn't that mean I'd need to fill them with concrete rather than drainage gravel?

EricL

https://www.workshop.bunnings.com.au/discussion/comment/134965#Comment_134965

Hello @johnnymac

Because it is only a single layer there won't be any need for reo bars. You also won't need to fill the blocks with concrete.

If you need further assistance, please let us know.

Eric

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