6 min read

How Water Drains Through an Artificial Lawn

Drainage is the part of an artificial lawn nobody sees and the part that decides whether the lawn is a success. Water has to get through the grass, through the layers below and away into the ground or a drain. If any one of those stages is blocked, you get puddles, moss and, in a pet garden, odour.

Here is how the layers work, top to bottom.

Through the grass

Latex backed grass drains through drilled perforations spaced across the sheet, which handles ordinary rainfall comfortably. Full polyurethane backing is permeable across its whole surface and clears water considerably faster, which is why it is the pet and heavy use choice.

Sand infill helps rather than hinders here, since it keeps the pile open and prevents fibres matting into a water holding layer.

The blinding layer

Immediately beneath the grass sits a thin levelling layer, usually granite dust or sharp sand, screeded flat. It has to be firm enough to hold levels and open enough to let water through. Building sand is the wrong material here, it holds water and sets hard.

The sub-base

Below that is compacted aggregate, typically 50mm to 100mm depending on ground conditions and use. This is the reservoir: water passes into the voids between stones and disperses. Over compacting fines or using the wrong stone closes those voids and creates a pan that water sits on.

Membranes and where they go

A weed membrane belongs between the soil and the stone, and often a second one under the grass. Membranes are permeable by design, so they do not stop drainage, but a folded, doubled over or clogged membrane can. Any membrane laid as an impermeable sheet, plastic damp proof membrane for instance, is a serious mistake in a lawn build up.

Falls and the ground below

On free draining ground the stone layer alone deals with everything. On the heavy clay common across much of Essex, water reaching the bottom of the stone has nowhere to go, so we design a fall across the base towards a border, a gully or a land drain running to a soakaway.

Levels around the lawn matter too. Grass finishing higher than the surrounding patio traps water; finishing slightly low against a permeable border lets it escape.

Diagnosing puddles on an existing lawn

Water standing on the surface almost never means the grass has failed. It usually means the blinding layer was over compacted, the wrong sand was used, the membrane is clogged with silt, or there is no fall and no outlet on clay ground. Occasionally it is simply that the lawn sits lower than everything around it and is receiving runoff.

Puddles where there should not be any?

Drainage faults are diagnosable. We will look at the levels, the base and the surroundings and tell you what is actually causing it before recommending anything.

Book a drainage check View Artificial Grass 07535 661664

Frequently asked questions

How fast should artificial grass drain?

A correctly built lawn is walkable within minutes of heavy rain stopping, with no visible surface water at all.

Why is water sitting on my artificial lawn?

Nearly always the layers beneath. Over compacted or incorrect sand, a silted membrane, an absent fall on clay, or runoff arriving from a higher surface are the usual causes.

Does artificial grass make garden flooding worse?

A permeable build up lets rain soak into the ground much as a lawn would. A sealed or badly built one behaves like a hard surface and can push water elsewhere.

Do I need a land drain under my lawn?

Only on ground that already holds water, typically heavy clay or a site with a high water table. We test the ground during the survey rather than adding it as standard.

Can drainage be fixed without lifting the whole lawn?

Sometimes. Localised problems can occasionally be solved with a drainage point or by adjusting the levels at the edge, though a base built wrong throughout needs redoing.