Building a retaining wall – in pictures

The retaining wall that became an urgent need after the Great Mud Flood of 2019 is described below in pictures.

This is what our backyard looked like, pre-retaining wall:

You can see that we have a brand new fence (installed mid-last year), but the retaining wall is a horrible mix of old perma pine, moss rocks, and stacked pavers. The stacked pavers were a stop gap measure added after the Mud Flood. You can see the after effects of the Mud Flood – there is mud everywhere! The first job after the retaining wall is built will be to pave over the remaining dirt, and then to power wash the heck out of the filthy paving stones.

When we bought our property four years ago, the fence was falling down behind three enormous conifers that were inappropriate plantings for the space (they were already huge, and were expected to double in size again). These were removed, and the built up soil you can see in the photo was rehabilitated by the addition of manures, compost, and organic matter. The soil is now very good, and we grow excellent veggies in it. It is a working veggie patch, but there is no need for it to look quite so horrible.

We chose to use a product called Garden Wall by Boral, which is a ready-made sandstone block that can be easily stacked and locks into each other. I say “easily” – but I am not the poor sucker lugging the damn things. They are extremely heavy. The cost of Garden Wall blocks varies, but we searched around until we found a good deal from a local landscaping business.

To prep the area, my husband had to remove a lot of soil. Barrows and barrows of the stuff. He removed it from the backyard, where we could not add it to the existing area (or we would have to keep building a higher wall), to the front yard. The soil in the front yard continues to be a work in progress due to previous plantings (some odd choices made by previous owners) and the accursed weed matting. The addition of some nice fresh soil could only do some good. I raked the new soil around the front yard while he dug and barrowed.

To create footings for the wall, he had to dig a trench. To guide him, he created a string line out of stakes and twine (see below), and used a level to make sure his trench was straight. You can see from the image below that they used infernal weed matting and black plastic in this garden bed as well – I continue to dig the bloody stuff up. The trench is about 20cm wider than the Garden Wall blocks, to allow for necessary drainage.

Once he had a nice flat trench, he laid 15cm crusher dust and tamped it down using a tamping tool:

Next, he laid paving sand about 5cm thick and tamped it down again:

This created a foundation for the blocks to be laid. Then he was ready to lay the first layer of blocks:

As he laid them, he checked each block to make sure they were level. He carefully tamped down each block.

After laying the first row, he installed blue metal gravel behind the blocks for drainage purposes, tamping it down again for neatness and to stop the backfilling soil from sinking.

He then stacked the next row, following the same process. Here you can see stage one, completed:

We are building an 18 metre wall that will run right around the entire garden bed. The garden bed runs right around the backyard – pictured here is only a small part of it. The wall will step down, as the bed slopes gently downward. So far, he has completed about 9 metres in three days, just in time for a weather system that is expected to bring with it at least 20mm rain.

I think he has done a great job!

Once the wall is built, we will pave up to about 15cm from the wall, and then plant up the remaining soil with some groundcover plants that will hold the rest of the soil in place.

A good reason to DIY, aside from personal satisfaction and accolades from your wife: this 18 metre wall will cost us under $4,000 AUD. Paying someone to do it (labour and materials) would cost us about $15,000 AUD. While we are happy to contract out tasks that we know we cannot do, my husband is also a pretty handy kind of person. He likes to learn new things and will take on tasks if he thinks he can manage them himself. In this case, he was fairly certain he could manage the task of building a retaining wall himself, if I was not fussed about how long it would take, given that we both work full time and would be doing this job on weekends. Saving $12,000 is a nice bonus. That will buy a lot of plants.