Laying Artificial Grass on Concrete: When It Works
Updated: Oct 9
Concrete or paving slabs make a workable base for artificial grass, and on a sound surface it is quicker than building a new one. The slab becomes the sub-base. What makes it work is getting water off the concrete (drainage holes where it puddles), laying a foam shock pad so joints and bumps do not show through, and gluing the grass at the edges and joins instead of pinning it. If the concrete is badly cracked, lifting or sits in a hollow that floods, break it out instead.
First, check the concrete
Before buying anything, look hard at what you have. This decides whether you lay on it or replace it, and it is the first thing we look at when someone asks us about artificial grass installation over an old yard or patio.
Good to go: Sound concrete or slabs that are firm underfoot, with only small cracks and minor dips. Cracks and undulations can be filled with a self-levelling compound before the shock pad goes down.
Borderline: Slabs that rock, a few sunken sections, or a patio with wide open joints. Re-bed or remove the loose ones first, then judge the rest.
Break it out: Large cracks where sections have lifted, concrete that is breaking up or loose, or a surface that slopes towards the house. Laying on top only hides the problem for a while. The concrete has to come out and the area be built like a normal lawn, with a compacted stone base.
Test the drainage
Water is the main problem with grass on concrete. Concrete does not let water through, so rain drains through the grass backing and then has to run off across the slab. If the slab has a fall, that is fine. If it does not, water sits under the grass and the lawn stays wet and smells.
Hose the concrete down before you start and watch where the water goes. Where it sits in puddles, drill 16mm holes through the slab and fill them with 10mm shingle so water can escape downward. On a slab with no fall at all, a row of holes along the low side does the same job.
What you need
Stiff brush, hose and (optionally) a jet wash
Self-levelling compound for small dips and cracks
Drill with a 16mm masonry bit and 10mm shingle, if puddles form
Foam shock pad underlay, usually 10mm or 20mm
Outdoor adhesive for artificial grass, gaffer tape and joining tape
The grass, a sharp knife and spare blades
Kiln-dried sand and a stiff brush
The method
Clean the surface. Brush and hose off dirt, moss and weeds, treat weeds if needed, and let it dry completely. Glue does not stick to wet or dirty concrete.
Fill and level. Fill small cracks and dips with self-levelling compound.
Drill drainage holes where the hose test showed puddles, and fill them with shingle.
Lay the shock pad. Roll out the foam underlay, cut it to size and tape the pieces together. It evens out small bumps, hides slab joints and makes the lawn softer to walk and fall on. 10mm is standard; 20mm suits play areas.
Glue it down. Run adhesive in bands about 200-300mm wide round the perimeter (roughly 2-3mm thick) and work quickly, because outdoor adhesive only stays workable for a limited time.
Roll out and cut the grass. Lay it with the pile pointing the same way, let it settle, and trim to size.
Join the rolls. Trim three stitches off each edge, leave a small gap, glue both edges onto joining tape.
Glue the perimeter. Fold the edges back, run a continuous line of adhesive with no gaps, and press the grass down. Keep off it until the adhesive has cured; check the tin, because times vary with temperature.
Infill and brush. Spread kiln-dried sand at about 4-5kg per square metre and brush it in against the pile.
Starting from a lawn rather than a slab is a different job, because how to lay artificial grass on soil means digging out and building a compacted stone base first.
Do you need a shock pad on concrete?
In practice, yes. Without one, every joint in a patio, every trowel mark and every dip in the concrete shows through the grass within weeks, and the surface is as hard as the concrete when someone falls on it. A free-draining foam pad also gives water a path to run along under the grass towards the edge or the drainage holes.
Edges on concrete
On a slab you cannot drive pins in, so the grass is held by adhesive. Where the concrete meets a wall or a step, glue tight to it. Where the slab ends at soil or a flower bed, the grass edge is exposed, so fit an edging trim or turn the grass down over the edge and fix it to a timber or steel edge set in the ground beside the slab.
Concrete, decking and balconies
The same idea applies to decking and balconies: a sound, drained surface, a shock pad, and adhesive rather than pins. Our service page notes that artificial grass can go over concrete, decking and other hard surfaces as long as drainage and preparation are right. On a balcony or roof terrace, check the structure and the existing drainage outlet with the building owner first.
Artificial grass on concrete questions, answered
Will it smell on concrete?
Only if water or pet urine has nowhere to go. A fall on the slab, drainage holes at low points and a free-draining shock pad stop that. On a dog run, rinse it more often than a lawn on stone.
Can you lay it on block paving or slabs?
Yes, if they are firm and level. Loose or sunken units need re-bedding first, and the shock pad hides the joints.
When is it better to replace the concrete?
When the slab is cracked through and lifting, breaking up, or holds water that cannot be drained. Then break it out and build a stone base, or consider a new hard surface: a resin bound finish can go over sound concrete as a patio or path (it will not drain through the slab, so the slab needs a fall) and gives a firm edge for grass beside it.
What is the best time of year to do it?
On concrete it is mostly about dry weather for the adhesive. The best time of year to install artificial grass on soil is wider because ground conditions matter more.
If you have an old concrete yard or patio in Wolverhampton and are not sure whether to cover it or break it out, Pete can look at it on a free site visit and tell you which will last.
