How to build a Besser block retaining wall?

Question

Hi,

We are hoping to build a small retaining wall in our backyard, to create a raised garden bed and then bench seat area. Here is a picture of our yard and the ChatGPT mockup of what we’re going for. From some quick research it seems interlocking blocks would be easier but we prefer the rendered look you can achieve with a besser block wall. Looking for some advice on how much compacting of soil/concrete base would be required. Then where/how to put reo into the wall and does it then need to be filled completely with concrete.

R4addZ · Answer

Hi @maddi.hancock

My initial concern is that in the render, the fence appears to be sat on the rear retaining wall and if you are using besser blocks the strength of the fence could be compromised due to the softness of the besser blocks. You would also need to get agreement from the neighbors to put the wall on the boundary as it will be visible from their side too. Have you considered using limestone instead as you can avoid the concrete foundation by laying the first row on it's side and the second row upright giving an L shaped wall where the weight of the soil on the base of the L supports the wall and the blocks are strong enough to support the fence.

Dave-1 · Answer

Good evening @maddi.hancock

Sorry we missed your question :/ I havnt laid a bessa block wall as yet tho have had my old one fall over as it was just sitting on compacted earth :) I had to break a section of it to install sewage pipes and after that the whole wall lost any strength it had, had.

@JacobZ's answer really has all the points I would follow, I would add the re-enforcing rods plus concrete to the inside of the blocks and not just mortar them together. The reason why is that I find later on when you go to dig your garden and are leveraging the soil there is a good chance you will force the block as well. Bit of extra now will save you hassels later on :)

@JacobZ mentions drainage, and I will mention it might be an idea to run some large conduits in the base with uprights for some low voltage lighting :) I am thinking 50mm pipes so you can easily run the cabling down them.

Dave

JacobZ · Answer

Hi @maddi.hancock,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

A rendered Besser block garden bed will need to resist any movement, as even a small amount of shifting can cause the render to crack. As a starting point for a small, low wall, I’d be looking at around 100mm of well-compacted road base beneath a reinforced concrete strip footing approximately 150mm thick, ideally with trench mesh. The footing should be at least twice the width of the besser blocks, so it should be approximately 400mm wide.

This will give you a solid, stable base to build your besser block walls on top of. Then, even better would be to have vertical reo bars cast into the strip footing, tied to the trench mesh and extending up into the besser block cells. The reinforced cells can then be filled with concrete to tie the wall and footing together. This will solidly attach the besser block walls to the foundation.

Horizontal reinforcement is not likely to be necessary as long as the height is kept below 600mm. If you are getting up around 800mm in height, then you'd likely want to consider adding a row of horizontal rebar, known as a bond beam, through the centre of the wall.

You'll also want to note that a garden bed like this will need to have a back, it can't simply sit against the fence. So, you'd need to build a separate wall at the back of the garden beds to prevent soil from pushing against the fence.

Drainage is also something you'll need to consider. Incorporating agi pipe that runs out of the garden bed to a suitable drainage point is essential.

You'll also want to waterproof the inside of the garden bed using a suitable sub-grade waterproofing product such as

https://www.bunnings.com.au/crommelin-4l-exterior-grade-brushable-waterproofer_p0961599?store=7369&gclsrc=aw.ds&gad_source=1&gad_campaignid=21122993677&gclid=EAIaIQobChMIkv-q8IeSlgMVv6dmAh3zqR6HEAQYAyABEgL4a_D_BwE

.

Allow me to tag our knowledgable members  @R4addZ, @Dave-1 and @Nailbag to see if they can add anything.

Jacob