Plenty of gardens and outdoor spaces have an old concrete slab or a tired patio that nobody loves but nobody wants the cost of digging out. Laying artificial grass straight over the top is an appealing idea, and the good news is that it usually works well. The important thing is to know when the slab is fine to grass over as it is, and when it needs a little work first. This guide covers both.
Can you lay artificial grass over concrete or paving?
Yes, you can, and it is one of the most common ways artificial grass is fitted. A sound, flat concrete or paved surface makes a perfectly good base, because the hard work of creating a firm, level foundation has already been done. Instead of digging out and building up a stone base, the grass is laid and bonded directly onto the existing surface.
That said, laying over concrete is not quite the same job as laying on soil. There are two things to get right: making sure water can still drain away, and deciding whether you want a softer feel underfoot. Sort those and the result is excellent.
Does the concrete need to drain first?
This is the question that matters most. Water drops straight through the holes in the grass backing, so it has to have somewhere to go once it hits the slab beneath. If it cannot drain, it will sit between the grass and the concrete.
Most patios and paths are laid with a slight fall towards a lawn, drain or gully, so water simply runs off the slab the way it always did. If that is your surface, you are in good shape. The problem case is a flat slab that pools water after rain, such as an old garage base or a dead-level yard. There the fix is usually to drill drainage holes through the slab at the low points, filled with gravel so water can escape downwards. Our drainage page explains when this is needed. Check how your slab behaves in heavy rain before anyone lays grass on it.
Do you need underlay or a shockpad?
You do not strictly need one, but on a hard surface it makes a real difference. Grass laid straight onto concrete takes on the hardness of the slab, which is fine for a small decorative patch but less pleasant where you will walk, sit or let children play.
A foam shockpad or underlay laid between the slab and the grass softens the surface, adds a little cushioning and helps even out minor dips in the concrete. The foam is designed to drain, so water still passes through to the slab below. For a patio, balcony or terrace that gets real use, a shockpad is one of the best small upgrades you can make.
How is the grass fixed down without pins?
On soil, artificial grass is pinned into the ground with galvanised nails around the edges. You obviously cannot drive pins into concrete, so a different method is used: the grass is bonded down with adhesive instead.
In practice that means running a strong outdoor adhesive around the perimeter and along any joins, so the grass is held firmly at its edges and seams without anything piercing the surface. The glue needs a clean, dry slab to grip, which is why the surface is swept and left to dry before any is applied. On larger areas, extra lines of adhesive or weighted boards during curing keep everything flat while the glue sets. Joins between rolls are glued onto jointing tape in the same way they would be on a soil base, with the pile running the same direction on both sides so the seam disappears. Done well, edge bonding holds the lawn just as securely as pins would on open ground.
Where there is a raised edge to work to, such as a wall, a step or a fence line, the grass is trimmed tight against it so no backing shows. On an open edge with nothing to glue to, a thin timber batten or edging trim bonded to the slab first gives the grass a firm line to be fixed against. It is these small finishing details, rather than the main glue line, that separate a neat job from a scruffy one.
When is it better to dig the concrete out?
Grassing over concrete is the easier, cheaper route, but it is not always the right one. It is worth digging the slab out and building a proper stone base instead when:
- The concrete is badly cracked, broken or sinking, so it no longer gives a stable, level surface.
- The slab holds water badly and drilling drainage holes would not be enough to clear it.
- The level is wrong, for example the slab sits too high against a door threshold or damp course once grass is added on top.
- You want the most natural feel, as a full stone base with a sand levelling layer gives a softer, more lawn-like surface than any slab.
If none of those apply and the slab is sound, there is little reason to take on the extra cost and mess of removing it. A good installer will tell you honestly which way makes sense for your surface.
Laying on balconies and roof terraces
Concrete and hard surfaces are exactly what you find up on a balcony or roof terrace, so the same approach applies, with a couple of extra points to watch. Weight is one: grass and a foam underlay are light, which is part of their appeal up high, but you should never block the existing drainage outlets or scuppers that keep the terrace from flooding.
Drainage is the other. The surface almost always already drains to a specific point, so the grass is laid to let water reach it freely rather than damming it up. A foam shockpad is especially welcome here, since balconies and terraces are places people sit and relax. We cover the specifics on our balconies page and roof terraces page. For most hard surfaces, though, the message is simple: if it is sound and it drains, artificial grass will sit on it happily for years.
Frequently asked questions
Do I need to clean the concrete before laying grass on it?
Yes. The surface needs to be swept clean and free of moss, loose grit and anything greasy, because adhesive only grips a clean, dry surface. Any weeds growing through cracks should be dealt with first too. A quick jet-wash and a day to dry off is usually enough before the grass goes down.
Will the grass feel hard underfoot on concrete?
It will feel firmer than grass laid on a stone base, because there is no soft ground beneath it. A foam shockpad or underlay softens that noticeably and is well worth adding on a patio or terrace you will stand and sit on. Without one, the grass takes on the hardness of the slab below.
Can I lay grass over block paving or a patio with gaps?
You can, but an uneven surface shows through the grass over time, and wide joints can telegraph through as faint lines. A foam underlay helps bridge small gaps and even out the surface. If the paving is badly uneven or rocking, it is better to lift and level it first than to hope the grass hides it.