Retainer Walls

Retainer walls reducing soil erosion, turn steep slopes into terraced levels, create focal points in the landscape. Retaining walls serve many purposes.

Well-built retaining walls transform unworkable inclines into usable outdoor space for the garden.

Despite their simple appearance, though, these walls require a good deal of planning—sometimes professional engineering, to keep their shape. Soil is heavy, especially when soaking wet from a recent rains, so a basic retaining wall (2400 mm long x 1000 mm high) potentially has to support up to 20 tonnes of soil pressure. With every additional metre of height, the pressure of the soil increases substantially. Miscalculate your construction plans, and you could end up with a weak wall that risks bulging or, worse, collapsing altogether. For just this reason, retaining walls taller than one metre should be designed by engineers and be constructed by the pros.

While we are at it, we also place a call to Dial Before You dig (phone: 1100).   A nationwide service that will notify local utility companies that you plan to excavate. Utility companies will send us plans of their assets and it is up to us to locate services before you excavate.

Retaining walls can be constructed using a variety of materials, from poured concrete and large timbers to natural stones, even bricks. Mr. Mac’s Home & Garden have built Timber Sleeper, Concrete Sleeper, Bush Rock, Sandstone, Besser block, Link Wall & Gabion Retainer Walls.  We Service all areas of the Gold Coast and South Brisbane. From Coolangatta, Elanora, Southport, Ormeau, Willowvale, Hope Island, Maudsland, Ashmore, Robina, Logan, Springwood and all areas in between. Whatever your needs we look forward to servicing you landscaping requirements.

Our retaining walls are only as strong as its Foundations. For a stacked-block retaining wall that’s no higher than a metre, a trench filled with 75 mm of crushed rock will help keep the wall from shifting and settling. The exact depth of the trench depends on the proposed height of the wall, but follow this rule of thumb: Dig a trench to be an eighth of the wall plus 75mm. For example, if you want the finished height of your retaining wall to be 900 mm tall, you’d need to dig the trench 200 mm deep to accommodate 75 mm of crushed rock and about 125 mm (or an eighth of the visible retaining wall) to start the wall below grade.

Another “rule of thumb” is that uprights get concreted into the ground 100 % of the height of retainer wall. Ie. If wall is 900 mm high, we concrete uprights 900 mm into the ground.

The first course (or row of blocks) sets the stage for the rest of the wall, so it’s vital that you make it perfectly level. If it isn’t, subsequent rows won’t be level either, resulting in a retaining wall that’s lopsided and unattractive. We ensure that the gravel layer below the first course of blocks is level before we start setting the blocks. Any discrepancies here will show up higher in the wall.

A wall that leans into the soil it retains is less likely to be pushed outward by soil pressure than a plain-old vertical wall. Design and build your retaining wall to slope at a minimum rate of 25 mm for every 300 mm of rise (height). Fortunately, working with retaining wall blocks makes it incredibly easy to achieve this “step-back” construction! The locking flange on the bottom edge of every block guides it to click into position slightly behind the lower block, preventing the top blocks from being pushed outward.

Groundwater is the natural enemy of retaining walls. When it saturates clay-type soils, they swell and put excessive pressure on the backside of the wall. To avoid failure, make drainage provisions at the same time as you go about building the retaining wall. Backfilling the space behind the blocks with drainage gravel and then installing a flexible perforated drainpipe (Agriculture Pipe) at the base of the wall could create the necessary escape route for groundwater. The perforated pipe will carry groundwater to each end of the wall where it can drain harmlessly away.

We always wrap drainage system in Geo Textile Fabric to keep drainage gravel free of soil. The ends of the drainpipe should then exit on each end of the wall, and you may cover them with crushed stone to camouflage their appearance.

After the drainpipe is in place, we backfill the rest of the space behind the blocks with drainage gravel. This allows water to filter through to the drainpipe at the base of the wall. For the best results, we backfill with a 100 mm of the material after laying each course of blocks, and use a hand tamper to compact the material. By tamping the backfill every 150 mm or so, you’ll ensure that it is packed tightly, which will provide additional support from the pressure of the soil behind the wall.

DON’T opt for a single tall wall if you can construct multiple tiered walls.

While retaining walls taller than four feet should be engineered by professionals, you may be able to DIY a solution for a tall slope by creating two or more shorter “tiered” retaining walls as opposed to a single tall wall. A series of short walls adds visual texture, and each individual wall will support less soil weight, ensuring that they’re less likely to fail. When building a tiered set of retaining walls, position the higher wall behind the lower wall at twice the distance as the height of the lower wall. For example, if the lower wall is three-feet high, the higher wall should be set back at least six feet from the lower one. This keeps the higher one from creating pressure on the lower one.