Retaining: What you need to know

Retaining in landscaping can create character and depth to your garden when used for raised garden beds, but as well as that retaining can be a crucially necessary part of the landscape when there are varying levels of the land, either on a sloping property or when there is a height difference between neighbouring properties.

Several construction materials and methods can be implemented to retain soil, and there can be a lot more to it than you may realise.

In Australia, some of the more popular methods for retaining soil, particularly between properties, are with limestone blocks, panel and post retaining, and timber.

As there are so many factors that may influence the best product to use, your best option is to request a free site inspection. Things you may not consider that the experts will, include factors such as accessibility, weight of the product, machinery needed etc. 

Be aware also that there are always the unforseens when any digging or excavating will take place. While all due care may be taken with locating the utilities and reticulation, it is impossible for a trades-person to know prior to digging what else may lie beneath. If you are aware of any tree stumps or difficult roots (palm tree roots can make digging very difficult) that may be in the way but not obviously so until digging commences, it is always advisable to inform your trades-person at the time of the site inspection so they are able to consider additional costs in the quote where possible. If you wait until work commences, everything may come to a stand still while additional costs are calculated, secondary discussions (between neighbours where it is between properties) take place, and additional necessary equipment is chased up. Your fence may end up down longer than was necessary.

Another consideration that comes with the scope of the job where it may be best to consult a trades-person, is knowing whether you will require a structural engineers report to be submitted to your local council for approval prior to the commencement of any work. Different councils may have different rules and restrictions when it comes to height and structural integrity of the retaining.

Above: A fence is being installed between properties with different soil levels. Panel and post retaining was already in place. but still wasn't high enough to meet the height of the higher property. Additional timber retaining was installed to keep the soil from the higher property off the fence, as using a Colorbond fence to hold back soil will make the fence lean and fall over time, and also rust out.

Above: From the other side of the fence (the higher property) once the fence installation was complete, only the top of the timber retaining is visible, as it holds the soil away from the fence. Bevelled limestone blocks retain the soil for the garden bed, to neatly define the garden from the paving.

Installing a fence on top of a limestone wall

Arguably, one of the tidiest looking Colorbond fence installations sits upon limestone blocks. Why the tidiest? Because instead of the Colorbond posts being concreted into a hole in the dirt, a neat, round hole is core drilled straight into the limestone blocks for the fence posts to sit in, then filled up with concrete nice and cleanly.

If there is a height difference in the soil between properties, that is if one house pad sits up higher than the other, installing a limestone retaining wall on the boundary will mean the fence can sit squarely on the boundary, with equal amounts of limestone block on either side.

Above: Prior to installing the large limestone blocks, an old asbestos fence was removed as well as some limestone garden edging. A tree stump had to be removed, and a string line set up to see what else might be in the way. The timber screening put in place further down the fenceline was to add height and privacy for both neighbours, since previously the fence sat lower (not on top of the retaining).

Above: Once all obstacles along the stringline are removed, the dingo can be brought in to lift the blocks into place (these big blocks weigh 240kg each!).

Above: One course of large, one metre limestone blocks have been installed to make up the height difference between neighbouring properties, ready for the installation of a new Colorbond fence.

Above: All of the Colorbond fence post holes are core drilled into the limestone blocks.

Above: The completed Colorbond fence with infill panels now installed, sitting atop the limestone blocks.

When installing a Colorbond fence and a limestone wall separately, be aware that any steel used to reinforce the limestone may present an issue in core drilling the holes for the Colorbond fence posts. New drill bits for a core driller can be costly, so talk to your fence installer prior to giving the go ahead on the limestone installation. Using larger limestone blocks can prevent the need for reinforcement.

Limestone Blocks garden edge/ planter box for experienced DIY or a Perth Trade Centre professional installation.

Installing a reconstituted limestone block garden bed

The clean look of modern reconstituted limestone block edging in a garden can make all the difference. The contrast between the defined line and sprawling garden gives the appearance of a well kept and cared for space.

With a number of products available to use as a garden edge/border, it is hard to beat the look of solid reconstituted block limestone edges/borders.

We have sourced the best materials available from the best suppliers here in Perth to accommodate almost any installation situation you require.

As experienced and professional Perth landscapers, it is fair to say that it has taken years to perfect some of our methods to ensure a first class job every time. Although that’s not to say certain jobs are out of reach of the average DIY Perth Landscaper, especially if you are already a bit handy.   

The pictures below show a before and after guide to what we would say is a simple limestone garden edge/planter box for a keen and experienced DIY gardener. This particular job was completed within a day as the ground was almost level to begin so it didn’t take too much to complete the project.

To begin start with ensuring your area is level to accommodate an approximate 50mm footing. If you have a laser level you can better gauge any low points, although a laser level would not be completely necessary, a simple longer length spirit level would be ideal. The ground does not have to be completely flat as you can re adjust the level with your concrete footing. Having the area flat will help when working out how much material you will need to mix. You can either mix in a wheel barrow using a mortar mixing rake or with a professional standard cement mixer.

Before making up your concrete footing mix, make sure you lay out your blocks first (with a string line) so you can see that you have enough blocks to fit, taking into consideration your (perp joins). This will help you to determine how many cuts you may need to make. Once you have determined what cuts you need to make to your reconstituted limestone garden edge this is the time to do it before the footing is put into place.

Make up your concrete footing as per specification, distributing with a brickies trowel or similar, running adjacent to the inside of your string line.

If you are going to install a two block height wall simply place the blocks on top of each other or measure out with a tape. As this particular job was accommodating to an existing wall, the space had to be exact to work into the customer’s requirements. This is the time to cut the top blocks.

Before placing the limestone edging blocks onto the footing give them a good soak with H2o. This will help keep the moisture from evaporating into the blocks as they will soak up any moisture like a sponge, decreasing the structural performance of the footing. When placing the blocks onto the footing, using a rubber hammer, gently knock them down into the footing approximately 10-20mm. This will provide a strong base.

When you have completed installing all the limestone edging blocks as per your design you can then join placing mortar into the perp joins. Once again using a mortar mix as per specification or a pre bagged mix.  

After applying using a small trowel or pointing tool, clean away excess using the trowel and a clean sponge (pending on weather conditions between one to two hours.)

Your project is complete and ready for plants. It is advised to request the advice of Perth Trade Centre's qualified horticulturist as to what plants are suitable to use in your new modern planter box.

As we have explained, it takes time to acquire the skill to perform certain methods so we have based our guide on an experienced DIY person’s ability to perform to their own level of expertise.

Alternatively, Perth Trade Centre can professionally install to your desired specification customising to your own unique Landscaping space.

Core drilling limestone blocks for colorbond fence installation

Where possible, core drilling limestone blocks is the preferred choice of most reputable fencing contractors.

Core drilling for a colorbond fence installation is generally considered the most aesthetically pleasing finish. When installed to a neat, level limestone block wall, the fence rails will sit flat on the surface exposing little to no gaps. The clean lines of the fence will compliment the wall and the wall will in turn compliment the fence.

Many people are not aware of how easy it is to install a fence with this type of installation method, although, as is the case with any building work, the correct equipment and knowledge is key to a successful fence installation.

Unlike installing with a post and panel type retaining system, the limestone block retaining wall can be installed to align the centre of the block with the centre of the surveyed boundary. When using a 1m x 350mm x350mm limestone block as a base for your fence installation, you can run the boundary with a 175mm centre (when installing a common fence), meaning the block will hug the boundary and will be exposed on just under approximately the 175mm boundary line taking into consideration the bottom rail dimensions. When installing on a Limestone block it is advised that the fence be installed in the centre of the block. This will not only look pleasing to the eye but will more importantly provide the fence base with the best structural support.       

The procedure is displayed and described in order of the pictures you see here from a recent Perth Trade Centre fence installation.

On this particular installation we were working with an existing natural limestone wall and screening an unsightly pre-installed picket fence that was installed on the outside facing wall.

The top of the wall is aligned, marked and core drilled using a core drill machine. It is very important to make sure the measurements are absolutely perfect. This is considered the most important part of the job.

The core is then removed leaving a hole that will accommodate the base of the fence post.

The bottom rail must be in line with the hole and boundary dimensions, also taking into consideration the size of the post.

The post is then lowered into the hole attaching to the rail joining from one panel to the next.