Artificial grass on decking, concrete and balconies

Artificial grass does not need soil. Some of the best-looking installations we see are on balconies, roof terraces, old concrete yards and tired decking, where a real lawn was never an option. The method is simpler than laying onto soil, because there is no dig-out and no sub-base, but three things decide whether it works: drainage, what goes under the grass, and how you fix the edges. This guide covers concrete and slabs, decking, and balconies in turn.

The short answer

Any hard surface that drains can take artificial grass. Lay a shockpad underlay first, roll the grass over it, glue the perimeter and any joins, and brush the pile up. Choose a short or medium pile, 18mm to 38mm, because there is no sand base for a deep pile to settle into. Budget about £10 to £22 per m² for grass and underlay together, and an afternoon for a balcony or a day for a yard.

Check drainage first

Whatever the surface, pour a bucket of water on it and watch where it goes. If it runs to a drain or off an edge, you are fine. If it sits in a puddle, the grass will sit in that puddle too, and it will smell in summer if there is a dog. On concrete, a puddle can be fixed with a self-levelling compound or by drilling a few drainage holes where it collects. On decking, water drains between the boards. On a balcony, check the outlet is clear and the fall runs towards it.

Perforated backing drains at well over 50 litres per m² per minute, so the grass is never the bottleneck. The surface underneath is.

Why you need underlay

Laid straight onto a hard surface, artificial grass feels hard, shows every line and joint in the surface beneath through the pile, and wears faster at the high spots. A 10mm foam shockpad fixes all three. It cushions the surface, bridges slab joints and deck board gaps so they do not telegraph through, and its drainage channels let water run underneath to wherever the surface drains. It also makes a big difference to how the grass feels to children, which is why it is used under play equipment.

Ours comes in a 15m × 1m roll, so a roll covers 15m² for £42, or about £2.80 per m². Lay the strips edge to edge, tape the joins, and cut to the perimeter with a sharp knife. It is loose-laid: the grass on top and the glued perimeter hold it down.

Onto concrete or paving slabs

1. Sweep and, ideally, pressure-wash the surface. Let it dry. Adhesive does not bond to dust or algae.
2. Fill any holes or wide cracks with exterior filler or mortar. Grind or fill any high spot that catches your foot; the shockpad hides small unevenness, not lumps.
3. Roll out the shockpad, butt the joins and tape them.
4. Roll out the grass and leave it for two hours in the sun to relax. Cold grass holds roll creases.
5. Position it with the pile leaning towards where you view it from, and trim to the edges from the back with a sharp blade, a little oversize, then in small passes.
6. Join pieces with joining tape and adhesive, pile running the same way, a 2 to 3mm gap.
7. Fix the perimeter: a 100mm bead of adhesive on the surface under the edge of the grass, pressed down, all the way round. On a large area, add a few beads through the middle so the grass cannot lift in wind.
8. Brush the pile up. Sand infill is optional on a hard base; a light dressing helps a longer pile stand.

Old slabs with wide joints benefit from a thin sharp sand screed brushed into the joints first, so the shockpad sits flat. If the yard is very uneven, a 20mm sand blinding held by a timber edge, exactly as on soil, is the proper fix.

Onto decking

Decking is a good base as long as the boards are sound. Rotten or springy boards need replacing first, because you will not be able to get to them later. Then:

1. Clean the boards and let them dry.
2. Screw down any loose boards and sink any raised screw heads.
3. Lay the shockpad with its channels running across the boards, not along them, so water can drain into the gaps.
4. Lay and trim the grass as above. Fix the perimeter with adhesive or, on timber, with galvanised staples or short U-pegs hammered into the boards every 200 to 300mm, just below the pile.

Air needs to move under a deck to keep the timber dry. Grass and underlay on top do not stop that, but do not seal the sides of the deck as well. If you are laying grass on a deck that is also being extended, consider laying it on the composite decking boards themselves; composite does not rot, so the grass can stay down for its whole life.

On a balcony or roof terrace

The same method as concrete, with three extra cautions:

• Weight. Grass and shockpad weigh about 3 to 4kg per m², which is nothing. Sand infill adds 5 to 8kg per m²; skip it, or check the balcony's load rating. Do not add a sub-base.
• Drainage outlet. Keep it clear. Cut the grass back around it or fit a small cover so the pile does not block it.
• Adhesive on a membrane. Many balconies have a waterproof membrane under the surface. Do not drill or peg through it. Adhesive is fine; if you rent, use a loose lay held by planters and furniture instead, with the shockpad giving it enough weight to stay put.

For a balcony, narrow rolls save a join. Jers, Lux and Rum come in 1m widths; everything comes in 2m. The 1m wide collection lists the options.

Which pile height

Without a sand base for the pile to settle into, very long pile can look untidy on a hard surface and holds more dirt. We recommend:

• 18mm (Rocco) for balconies, roof terraces and anywhere it will be walked on constantly. Neat, light, easiest to keep clean.
• 30mm (Talya, Jers, Lux) for a yard or patio that should look like a lawn. The all-rounder.
• 35 to 38mm (Bul, Dan, Val) with a shockpad for a family patio you will sit and play on.

The pile height guide goes into the trade-offs.

What it costs

For a 3m × 4m patio in Talya 30mm: a 4m roll cut at 3.1m is 12.4m² × £8 = £99 of grass, one shockpad roll £42, a tub of adhesive £9.60, about £150 all in, plus delivery under £190. No tool hire, no skip, no dig. The cost guide compares this with a lawn onto soil.

Common mistakes

• Skipping the shockpad to save £42, then seeing every slab joint through the grass.
• Laying over a puddle and blaming the grass for the smell.
• Gluing the grass the day it arrives, before it has relaxed, and living with the roll creases.
• Cutting from the front. Cut from the back; the fibres stay intact.
• Pegging through a balcony membrane.

Order free samples, lay them on the actual surface, and look at them in the light the space gets. If you are unsure whether your surface will take it, send a photo to support@yumihome.co.uk or call 0161 399 1792.