Quick Answer:
80/20 turf underlay is a sand-based rootzone mix made from roughly 80% sand and 20% finer material such as loam or organic matter. It is used under turf to improve drainage, create a level base, and support healthy root establishment.
Getting the base right is one of the most important parts of laying turf. Even the best turf will struggle if it is laid on poor soil, which is where 80/20 underlay comes in.
Understanding the 80/20 Mix
The name comes from the ratio:
- 80% sand → improves drainage and stability
- 20% soil/organic matter → provides nutrients and moisture retention
This combination creates a balanced foundation that supports both drainage and plant health.
Why this matters:
Too much clay or heavy soil can hold water and cause turf to fail, while too much sand alone won’t provide enough nutrients.
Why 80/20 Turf Underlay Works So Well
The mix is specifically designed for turf installation:
- Allows water to drain properly
- Prevents waterlogging
- Supports strong root establishment
- Creates a level, stable surface
For example, in areas that experience heavy rain, good drainage is critical to prevent turf from becoming waterlogged and damaged.
Where 80/20 Underlay Is Used
It is commonly used for:
- New lawn installations
- Replacing existing turf
- Preparing uneven ground
- Improving poor soil conditions
It can also be used under instant turf rolls to ensure they establish quickly and evenly.
How Deep Should It Be Applied?
A typical application depth is:
👉 50–100mm
The exact depth depends on the condition of the existing ground.
- Poor soil → deeper layer
- Good base → lighter layer
80/20 vs Other Soil Mixes
Compared to standard topsoil:
- Better drainage
- More consistent structure
- Designed specifically for turf
Compared to pure sand:
- Holds nutrients better
- Supports healthier growth
Why this matters:
Using the wrong base can lead to patchy growth, poor drainage, and long-term lawn issues.
Practical Example
If you lay turf directly onto compacted clay soil, water may sit on the surface, leading to root rot.
By adding an 80/20 underlay layer, you create a buffer that allows water to drain while still supporting the turf.
Why It Matters Long-Term
A proper underlay:
- Improves turf establishment
- Reduces maintenance issues
- Extends the life of your lawn
Skipping this step often leads to uneven growth and costly fixes later.
Can I lay turf directly on soil?
You can, but results are usually better with a prepared underlay layer.
What is the difference between turf underlay and topsoil?
Underlay is designed for drainage and stability, while topsoil is more focused on nutrient content.
What is turf underlay used for?
It creates a stable, well-draining base for laying turf and supports healthy root growth.
What is the best thickness for turf underlay?
Typically 50–100mm depending on site conditions.