You’re tired of your concrete patio’s boring look so you want to replace it with a beautiful lush grass. But will the concrete under the lawn allow the turf to thrive?
Replacing one with the other may come in costly if you are not well-informed. Often, unfounded decisions result in multiple reapplications of turf, costing the owner a fortune.
What about factors such as soil moisture and root development? All necessary for a healthy bright green grass? How about artificial turf – if placed over a concrete patio would the drainage be a problem? Let’s answer all the questions.
Can laying grass on concrete be a successful long-term project?
Putting a little soil over the concrete surface won’t do the job. The grass needs to establish its roots properly. Concrete is solid, it easily heats up in the summer and isn’t as porous as soil. With that in mind, to answer the question of whether laying turf on concrete is possible:
Yes, it can be done, but only with artificial turf, because there is no need for plants support this way. The synthetic grass will fit well on the concrete and won’t require additional maintenance.
Using real grass is highly undesirable as it will most likely have issues with staying alive. The concrete underneath will hinder the soil’s moisture-retaining properties. Also, proper drainage will be a serious problem. If you absolutely want real turf, it is really best to hack out the concrete first.
Laying Artificial Grass on Concrete (and other hard surfaces)?
Things to consider when laying synthetic grass on concrete:
Laying synthetic grass on paving slabs or pure concrete is easy and doesn’t require much maintenance afterwards.
- Installing a shock pad to soften the surface is usually part of the process. It also has the property of smoothing out slight imperfections (a flat surface is needed for installing the artificial turf). If you are a cat or dog owner note that a shock pad is not recommended, because the urine bacteria tend to stay in the underlay. Learn more about preventing cats from pooping in your garden.
- A couple of holes need to be drilled in the cement for a better drainage (in case of puddles forming thereafter spraying it with a hose). After all, you don’t want ponds in your yard after every rainfall.
- A slight gradient may be enough for the water to run off, but it really depends on the condition of the yard itself.
- Larger gaps in the concrete should be filled in before the turf laying as they will result in sagging and a poor overall quality of the job.
How to install astroturf on a FLAT concrete surface?
The grass needs a really smooth and clean surface or the laying will result in bumps or sagging and it won’t look natural. Artificial grass is suitable for all kinds of hard surfaces including decking, slabs and tarmac, asphalt and tiles so long as they are flat.
Here are the exact steps on how to lay astroturf on a concrete base successfully:
- Take measurements – measure the area you want to be covered with grass. This way you will know exactly where to cut, fix, glue and drill later in the process.
- Sweep the concrete clean – clean all dirt, sand, moss or weeds off the concrete. This is best done by pressure washing it down but if you have a leaf-blower, it could also do the job. The surface needs to be smooth and clean to allow the synthetic turf or underlay to fit in as closely as possible.
- Hose the concrete with water – If you did the power wash, a second hosing won’t be necessary. This is done to establish if there are puddles forming on it. If there are such puddles you’d have to make sure the concrete drains properly. An ideal base would have a slight incline for the water to run off. But in case of puddles forming…
- Drill holes where puddles form –
Make sure you drill all the way through the concrete. It’s best if you see the soil through the holes. If you can not be sure, hose again after the drilling and see if the holes are getting filled with water or the water is flowing down, through the soil. By doing so you ensure that the water has someplace to go and won’t sit on your newly laid astroturf after a rain.
- Fill the holes with kiln dried sand – The sand will act as a drainage system medium.
- Wait until the surface is dry – If you did not pressure wash, sweep the concrete one more time after it has dried out. This way you are getting rid of the bumps and providing a flat surface.
- Lay a shock pad underlay – It’s recommended to use a 25mm thick underlay. Leave some space of about 65mm for each side of the perimeter. You will later fill this in with adhesive.
- Cut the artificial grass – you will need a sharp knife. Unroll the grass and do the cutting. Be precise as this can only be done once. Never cut close to your knees when kneeling down. Cutting through the synthetic needs constant pressure. At the end of the cut, the knife may come out too fast and injure you.
- Position the artificial patches over the shock pad – lay them so their joints touch one another. It is very important for them to be perfectly placed next to each other. Make sure the grass is aligned in the same direction or you risk having a visible seam.
- Place joining tape underneath the seam – use an artificial grass joining tape and carefully run it across the whole length of the seam between the two patches of fake turf.
- Glue the grass together with adhesive – apply the fake grass adhesive (that you have previously prepared) in zig-zag across the tape.
- Press firmly when joining the grass – make sure the grass connects perfectly and leaves no visible seam. After that run your hand across the already glued seam to ruffle the fake grass blades. This will additionally hide the seam.
- Apply glue at the edges of the perimeter – apply adhesive on the spacing left from when you were installing the shock pad. Make sure to squeeze a continuous line of glue across the whole length of each side.
- Wait a few hours for the glue to cure – Do not walk on the astroturf for the next 2 to 3 hours after the application. This step is to ensure the grass is firmly stuck on the ground.
- Brush the grass with silica sand – Apply 5 kg of silica sand per square metre. Use a broom to brush into the grass, with movements opposite to the direction in which the grass is running. The sand will fill in the gaps in the “net” of the artificial grass. This will help the synthetic fibres stay upright (artificial grass with thatch doesn’t need that) and therefore enhance the overall aesthetics of the green cover. Another important feature of the sand brushing that will be of use here is the sand’s weight. It will fix the grass to the ground, rendering it unable to shift.
Laying artificial grass on UNEVEN surfaces such as paving slabs
The desired surface for your astroturf should be flat and smooth. Gaps between the slabs should be ultimately filled with some sort of medium.
If the imperfections are small, a foam underlay will be enough to correct them. If you have weeds growing between your block pavings, use a weed killer and manually remove them. You should then install a weed-suppressing membrane.
If the bumps and gaps are too pronounced, however, you’d need to fix that before installing the artificial grass. Here is how to prepare uneven concrete or paving for artificial grass laying:
- Use a layer of sharp sand and level it – you need to compact the sand first, which is best done with a vibrating plate compactor. After that, you need to manually level it. Don’t forget to leave spacing around the perimeter where you will later apply adhesive. The glue is usually waterproof which will keep rain away from washing off any sand.
- Use a self-levelling compound – this is a type of cement that is especially used in levelling concrete. It’s used prior to installations of different types of flooring as they all require a flat surface. Follow the manufacturer’s instructions and you won’t have any issues applying it.
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Issues around real turf and shallow soil
If you really can’t agree on removing the concrete and insist on using real grass, then you won’t have it easy. Real turf over a concrete foundation will need a minimum soil layer of 25 cm. You should choose a shallow-rooted species as well. The roots need to find their nutrients and water deep down in the soil. Even then you’d need to drill holes in the cement base (every foot or so) to improve the drainage. If the patch doesn’t drain well the water will prevent oxygen from entering the soil and your turf will die out real quick. Apart from that, you’d have to water it profusely (every day) during warm summer days. The water will evaporate very quickly in such a shallow patch of soil. A fertiliser should also be used as the grass won’t be able to feed off the soil’s nutrients.
Do leave a comment below if you feel you need more answers!
Header image source: Shutterstock / By Baanrukbua
Posted in All About the Lawn
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