As an approximate guide, one bulk bag will cover:

• 10–12m² at a depth of 50mm

• 6.5–7.5m² at a depth of 75mm

• 5–6m² at a depth of 100mm

Garden borders, rockeries, and footpaths commonly require around 40mm to 50mm of decorative slate, while domestic driveways and heavy foot-traffic areas typically require 50mm to 75mm depending on the ground conditions and sub-base.

These figures are estimates only. Actual coverage will vary according to the bag weight, ground conditions, compaction and the accuracy of the excavation.

Not sure how many bags you require? Call our Rugby team on 01788 866945 with the length, width and required depth.

20mm blue slate decorative chippings are intended as a decorative surface, border, or driveway topping. Colour, natural shade variations when wet or dry, and flat angular shape can vary according to the source of the slate.

Excavate the area to the required depth and prepare the ground appropriately. A suitable geotextile membrane may be required to prevent weed growth and stop the subgrade from mixing with the slate.

Spread the 40mm blue slate evenly over the prepared sub-base to the recommended depth, typically around 50mm to 75mm for borders, rockeries, and garden paths. Rake or lay the slate by hand to ensure an even, flat distribution across the entire area.

Check the finished surface level and slope to ensure proper drainage away from surrounding structures. Ensure the slate depth is consistent to prevent exposed patches or uneven surface layers.

Requirements vary according to ground conditions, loading, and the intended use of the surface. Follow the project specification or seek professional advice where appropriate.

Available for collection from our Rugby branch or local delivery using our own fleet.

Bulk bags will normally be delivered by a crane-equipped lorry. Delivery is kerbside and the final offloading position is always subject to safe access and the driver’s discretion.

Please tell us before delivery about:

• Narrow roads or restricted entrances
• Parked vehicles or limited turning space
• Overhead cables, trees or other obstructions
• Soft, sloping or unsuitable ground
• Any other access concerns

Enter your postcode on the product page to check your delivery area. We’ll confirm the delivery date after your order is placed.

What is 20mm blue slate?

20mm blue slate is a decorative aggregate made from crushed natural slate rock. It consists of smaller, flat, angular pieces with rich dark blue, grey, and subtle violet tones.

What is 20mm blue slate used for?

20mm blue slate is commonly used for garden pathways, borders, rockeries, plant toppers, and around water features. Its smaller size creates a flatter, smoother surface that is easy to walk on.

What is the difference between 20mm slate and 40mm slate?

20mm slate features smaller pieces that lie flatter and pack down more tightly, making it more comfortable for footpaths. 40mm slate consists of larger, chunkier pieces that provide a bold, highly textured finish for large ground covers and rockeries.

Is 20mm blue slate fish-friendly?

Yes. Slate is an inert, natural rock that will not alter the pH level or chemical balance of water, making it completely safe for ponds, fish, and aquatic features (rinsing beforehand to remove quarry dust is recommended).

Does 20mm blue slate fade in sunlight?

No. Natural slate is UV-stable, weather-resistant, and non-porous. Its natural blue-grey shades will not fade, wash out, or bleach in direct sunlight over time.

Why does the colour of blue slate change?

Being a natural stone, 20mm blue slate displays a soft, matte greyish-blue appearance when dry. When rained on or wet, the colour deepens dramatically into a rich, dark midnight blue.