How can concrete be used in garden landscaping?
As a natural material, concrete is an easy option when it comes to choosing materials for your garden. Whether you’re putting in some concrete edging to your flower beds, adding a concrete garden bench as a focal point, or looking to add structure to a tiered garden, it’s a choice that comes with many benefits.
As well as versatility, durability is one of the main characteristics. Your garden is open to the elements, and concrete is able to withstand extreme winds, heavy rainfall and fluctuating temperatures, without ever shifting from its original form.
Constructing paving and stepping stones
Starting at the floor, one of the most common ways you’ll see concrete used in gardens is through paving slabs or stepping stones.
To install these you don’t need a huge amount of equipment or experience — just a mallet, spirit level and a bit of patience.
The trick is to dry lay the patio or stepping stones before you go anywhere near mixing the concrete you’ll use to fix them in place. You’re checking that the right size slabs go in the right places, that the layout you have in mind works in the space, and that you have enough to finish the job.
Between the foundation mix and paving, the total depth needs to be approximately 150mm to provide the necessary stability.
- 50-80mm hardcore - compact the sub-base to provide stability for what’s going to sit on top
- 50-80mm concrete - a C25 mix will give the right blend of cement and aggregates for laying slabs
- 18-24mm paving - slabs come in all shapes and sizes, but the depth you choose should be based on budget and how much foot traffic the area will get
The exact depths depend on the soil type and what’s directly next to the patio you’re putting together.
For patios that adjoin a house, your patio should sit 150mm below the damp proof course to allow for effective drainage, meaning a total of 300mm for the foundations.
One of the major factors to consider that differs from most other structures is the need for a slope, so water doesn't congregate on your patio, and runs away from the foundations of other structures. The trick is to do so in a way that water has somewhere to go, but the slope isn’t immediately noticeable once you put furniture on top of it. A fall of 1cm for every 60cm would be plenty, meaning a 3m wide patio needs 50mm of fall.
A good quality, heavy paving slab is stable almost from the moment it’s installed, but you should still aim to give it 48 hours before walking in it to allow it to bond effectively with the foundation mix.
With the trend for inside / outside living and bi-folding doors stemming from open plan kitchens, polished concrete floors are also making an appearance in gardens. This obviously comes with the danger of slipping, so if this is your preferred style, look to add an epoxy or polyurethane coating to make it more secure underfoot.
How to build a retaining wall
Not every garden is configured in a way that allows you to enjoy it to its fullest extent. That’s where garden retaining walls come in, allowing you to flatten out areas of ground, compacting the earth you’ve moved behind a neat set of bricks or concrete structure.
Built correctly, with sufficient drainage built in, they’re both solid and aesthetically pleasing, and possible to finish in a way to work seamlessly with the rest of your garden.
While bricks and poured concrete are viable options in some instances, the most common method is blocks, which can be constructed to the exact shape you’re looking for.
After designing what it is you plan to build, the first step is digging the trench. This needs to be deep enough for a full block to be submerged and for approximately 200mm of a base material to sit below it. A level trench means well-distributed foundations, which in turn means an even wall.
Once the trench is compacted, lay a crushed stone base then begin to place your blocks, getting each one level with a spirit level and mallet. Even a tiny stone on top of your blocks can put them out of line which will ripple through the rest of your structure, so make sure everything is well swept before making a step up.
While there are mortar-free block options on the market, the most common way to fix your structure in place is with a series of steel rods and a concrete fill. Soil is heavy, so the wall you put in place to keep it back needs to be also.
That’s one of the reasons you shouldn't build too high. A concrete retaining wall reaching above 1.2m would be a risk and it’s at that point where you need to consider a tiered approach instead. This is something that needs to be done in the design stage, as trying to factor this in later on in the project will mean considerable disruption.
Aim for a tier sitting at least twice the distance of the height of the wall below it. So for a 1.2m high wall, the next tier should begin 2.4m away.
Once you’ve added the appropriate drainage and backfilled your structure with stone, it’s time for the topsoil and then whatever else it is you want to add to the new section of your garden.
Building concrete bench planters
Many retaining walls will actually be used to house plant beds, but separate concrete planters are also a great addition to a garden, and suitable for many types of plant.
The one thing you need to consider is the alkaline levels that naturally exist within concrete. It’s not a substance that works well with soil and something that may seep in and affect the growth of plants.
The last thing you want to do is go to the time, effort and expense of putting a planter together to then see your plants fail to flourish.
Treating your planters with the right sealers will help them last longer, and protect the soil from contamination. Much of this can be done with water, naturally reducing the salt and alkalinity. After that, a vinegar solution can be added and left to soak for a couple of hours before painting with a coat of concrete sealer and leaving overnight.
Your concrete planter is now ready for soil, however, you should continue to water once a week with a light vinegar solution to help counteract any build up of salt on your planter.