lumpy bumpy artificial grass reasons and solutions

Three reasons why your dream lawn could turn into a perfect nightmare…

It’s an unfortunately common scenario – a once perfect looking artificial lawn is now lumpy and bumpy – better resembling a crazy-golf course than the lawn you always dreamed of.

Whether it’s six, eight, twelve months or more since your initial installation there are a few common reasons why lumpy, bumpy artificial grass happens and they all come down to bad groundwork. Always employ a professional and you will avoid these pitfalls. These two points are the most common reasons for lumpy bumpy artificial grass:

1: Inadequate turf and top-soil removal from the underlying lawn area.  One of the main objectives when removing the existing lawn area is to find a ground level that is sufficiently firm and well-draining upon which to build a base for your artificial turf.  Grass and topsoil form a spongy ground layer and this is not adequate for the uniform support of synthetic turf.  There are no ‘one-size-fits-all’ methods to this and often it may mean digging deeper in some areas than others.  It may even mean digging deep holes in some areas until you find that level.   It is not sufficient in most circumstances just to skim the very top layer of grass and topsoil.  100mm depth should be achieved as a very minimum .

Also related to this same point – if artificial grass is laid over real grass, twigs, plants or other similar organic material the grass will become uneven as the organic material decomposes at different rates.  It is essential to remove all of this type of organic material during the installation process.

2: Inadequate base construction.  Base construction can vary from contractor to contractor but there are a few key characteristics you need from a good artificial grass base:

  • to provide a firm but forgiving base
  • to drain freely
  • to be free from organic material that can decompose and encourage habitation by living organisms

This is why we recommend the following as standard:

  • a ground-stabilising geotextile to separate the existing stripped back lawn area (soil) and your new base. Without this geotextile a base will slowly compact into the soil which over time will result in the lawn becoming lumpy and bumpy. This geotextile will also act as a weed barrier at the bottom of your base rather than at the top which is where weed barriers are more commonly (and less effectively) used.
  • a sub-base constructed from compacted quarried stone aggregate (don’t buy recycled it can contain contaminates which may decompose and other more hazardous impurities like nails, glass or wire.)  Ideally we recommend this to be 100mm deep or more made up of 75mm compact DTp1 and 25mm of quarried 4mm to dust as a surface layer or similar.
  • a final base constructed from compacted crushed quarried stone aggregate such as 4mm to dust.  We recommend carboniferous limestone for this. This sub-base and  base should be built up in layers compacting with a wacker plate or vibrating roller every 75mm.

This base construction will provide everything you need for a lawn that drains well, never loses shape and is forgiving enough to absorb the impact of a fall.

A note about sand.  Many installers recommend sand as a final base layer for artificial grass.  We recommend a 4mm(+) to dust (sometimes known as stone dust) over sand for a number of reasons:

  • stone dust compacts better.  No matter how many times you run a wacker plate over sand it won’t lock together to provide a sufficiently firm surface.  Stone dust will.
  • sand holds more moisture.  This means it will also hold more bacteria (especially relevant if you have pets) and it will also affect the lawns ability to drain.
  • sand provides a better rootzone for seeds germinating in the grass thatch with roots finding their way through drainage holes.

3: Plant bulbs. This goes back to the first point but it’s such a potentially big issue (and a common one) that we thought it was worth mentioning on its own. Bulbs are stores of energy waiting to burst out of the ground at the first opportune moment.  Bulbs don’t need direct sunlight to grow, just the right combination of heat and moisture.

Bulbs can create monstrously alien looking formations underneath artificial grass.  Artificial grass can actually even aid and speed up the growth of bulbs by providing ground insulation!

The key thing to remember here is to make sure the ground where you are going to install your artificial lawn is free from plant bulbs.  This is especially relevant if the new artificial lawn area is going to go over previous planting areas such as flower beds.


We all have our different ‘qualifiers’ that we look for when we are choosing a contractor – for some it may be down to price, availability or just because a contractor seemed honest, for others it may be because they support the same football team, love rock music or have a nice beard ;).  The main thing to look for is a dedication to quality, comprehensive knowledge and evidence of experience doing similar work.  A contractor should perform a full survey of your garden before they can tell you exactly how they are going to do the work.  ‘One size fits all’ approaches should be avoided as you’d only be employing someone who does ‘artificial lawns by numbers’ rather than someone who has a genuine understanding of what they are doing.  Avoid making decisions based purely on price – poor quality artificial lawns are a cost and a constant disappointment.  Good quality artificial lawns are an investment and will be enjoyed for many years.  If price is your key qualifier compare written quotes like for like to determine true value for money.

A picture of a commercial artificial grass installation in Horfield Bristol by Turf King

a picture of a Turf King artificial grass base being constructed from DTp1 on Terram 1000

Belle warrior wheelbarrows and cement mixer in Marshfield, Wilts
About Turf King

Turf King is a Bristol based supplier and installer of artificial grass across the domestic, sports and education markets.  We are an independent family business dedicated to excellence in artificial grass.  Through our blog we aim to give buyers of artificial grass all the tools they need to make good purchasing decisions when buying artificial grass product and services. Follow the Turf King blog for regular updates.

Top Turfing Tip | good questions to ask your contractor

These are the three main questions we’d recommend you ask your potential contractor in regards to groundwork:

1: How much soil will you need to remove?

This will ultimately depend on the final intended ground level of the new lawn.  We recommend the need for a minimum of 100mm of compact new base material so if the new lawn is going to be the same level as the old lawn then 100mm + the length of the grass product should be achieved as a minimum.  Exact base construction (and depth) will depend on the existing ground conditions.  It’s also worth noting that if ground level is to be brought up significantly then it may not be necessary to remove any grass and soil.  Providing the grass is short an existing lawn can be firmed up with 75mm DTp1 compacted directly into the lawn and topsoil before installing a ground stabilising geotextile and building the new base accordingly.

2: Will you be installing a membrane and if so how?

Ideally the contractor will be installing a non-woven ground stabilising geotextile between the soil sub-base and the new aggregate base to stop aggregates ‘pumping’ into the soil over time.  A landscape fabric or weed membrane on top of the aggregate base provides no ground stabilisation and will most likely result in uneven ground over time.  If installed between the soil sub-base and aggregate base the geotextile will perform much better as a weed barrier than a landscape fabric directly underneath the artificial grass.

3: How will the base be made up?

Look for quarried aggregates over recycled.  Ideally a combination of grades (we recommend a minimum of 75mm compact DTp1 and 25mm 4mm to dust in the paragraph opposite but the exact construction will depend on the existing ground and take into consideration any drainage or soft ground issues.  Ultimately you are looking for someone who seems to have a good knowledge of what they are talking about rather than a contractor who just recommends sharp sand or similar.

Artificial Grass Surveys

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We offer a comprehensive professional survey service with written report which can be used as legal evidence in the case of bad practice. Surveys are chargeable but can be qualified over the phone for free.  Qualification is no guarantee of successful conviction.  Get in touch today for more information.

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t: 01179 807905

e: [email protected]

p: 35 – 37 Whitehouse Street, Bristol, BS3 4AY