Rock Bags FAQ

In this Rock Bags FAQ, you will find the answers to the most common questions we get about this product we’ve been distributing across ANZ since 2016.

What Are Rock Bags?

Rock Bags, also known as filter units, are a simple product consisting of a large mesh net bag filled with small rocks. They are used for erosion control in ports and coastal areas, bridges, railways, rivers and waterways, roadways, and offshore sites.

Who Invented Rock Bags?

Kyowa, a Japanese manufacturing company, developed these Rock Bags in 1987 to protect the foundation structures of the 3911-metre-long Akashi Kaikyo Bridge from erosion. The bridge connects Honshu Island to Awaji Island over the turbulent Akashi Strait. The success led to Rock Bags being popularly used worldwide for numerous projects.

How Many Rock Bags Have Been Installed So Far?

As per the latest data, more than 1,300,000 Rock Bags have been installed in over 24,000 locations worldwide for different erosion control and civil engineering projects. 

When were Rock Bags introduced to Australia?

Bluemont first introduced Rock Bags to Australia in 2016. 

How do Rock Bags work?

A rock bag filled with many small rocks is similar, in effect, to one large rock. However, its flexible structure and easy deployment make it more effective than large rocks used for erosion control. Rock Bags act as a protective barrier, preventing water from washing away the sediment. 

What are Rock Bags made of?

Rock Bags are made using 100% recycled polyester. The flexible mesh netted bags are filled with lots of small rocks or other similar products such as concrete pieces. 

Are Rock Bags strong?

Yes. The sturdy material of Rock Bags can hold up to 8 tonnes of rock. The polyester material is highly durable, rip-resistant, and long-lasting. 

Does Bluemont provide rocks too?

No. We only supply the empty Rock Bags and lifting rings required during deployment and installation. 

Where are Rock Bags manufactured?

Japan. Rock Bags are manufactured by in Japan, using 100% recycled materials. They comply with the globally-recognised quality standards.

What is the rock type I can use to fill Rock Bags?

Sturdy rocks between 50mm-175mm in size and a specific gravity of 2.6 – 2.65.

Do I have to prepare the ground before installing Rock Bags?

In most cases, it’s not necessary. That’s one of the benefits of the Rock Bags, as you can just lay them on the surface. The flexible structure of Rock Bags adjusts to uneven surfaces well.  

Do I need to weigh each bag when filling it?

No. The filling frame provides the correct filling level for each bag size. If you fill the rock bag until it reaches the top of the frame, you have filled it to the correct level. 

How long does it take to prepare a rock bag?

Based on our experience in past projects, it takes about 5 minutes to fill, prepare, and stockpile Rock Bags for installation. It is a quick job that can be done with an excavator. 

How long does it take to install the Rock Bags at the site?

Deployment and installation usually take 5-10 minutes. However, it can change depending on the time required to transport the stockpile to the project site. 

Does Bluemont provide training on handling Rock Bags?

Yes. We offer on-site training for clients upon request. In addition, we also provide brochures and videos demonstrating how to fill, install, and maintain Rock Bags step-by-step. There are plenty of resources to help you. 

Can Bluemont provide suitable designs for installation?

Yes, absolutely. We can offer simple designs that portray the rough structure based on our past projects. We can also provide comprehensive designs with all the engineered details with the help of independently certified engineers.

While Bluemont staff are not engineers, their expertise and experience working on similar projects help them offer feasible design ideas. They will consider the nature of the project, installation area, rock bag size, and other factors to provide comprehensive support.  Bluemont also has access to qualified engineers for complete engineered designs as required.

How long does delivery take?

We have stocks of Rock Bags in our warehouse located in Brookvale, NSW, to dispatch your order immediately. Freight shipping to the eastern seaboard takes only 1-3 days, and shipping to the western or northern seaboard takes approximately 5 days.

How are Rock Bags packaged for shipping? 

Depending on the order quantity, we package them in carton boxes, pallets, or crates. 

Is there a minimum order quantity?

Yes. The minimum order quantity is the bundle size;

What are the payment terms?

The full payment must be made prior to shipment unless agreed otherwise beforehand. 

Can I get a discount on Rock Bags?

Yes. Bulk purchases are entitled to discounts, and we offer a price reduction per crate. Please contact Bluemont for more details. 

Do Rock Bags come with a single or double net?

Both. There are various types of Rock Bags. The Eco-green Rock Bags feature double netting. 

Does Bluemont ship worldwide?

Bluemont operates in Australia, New Zealand, and the Pacific Islands (ANZ Region). 

Can I get the weight and size of Rock Bags customised from Bluemont?

No. Rock Bags only come in readymade sizes, designed to bear 1, 2, 4, and 8 tonnes.

What is the maximum weight per bag?

Depending on the size of the bag, it can be 1, 2, 4, or 8 tonnes. Each bag should be filled accurately as possible to meet its optimum capacity. The filling frame designed to hold the particular bag size is the best method to determine the maximum volume of the bag. Simply fill the frame to the top. 

Can I use Rock Bags as a solution for scouring?

Yes. Rock Bags have undergone many lab tests over the years, proving their efficacy in scour protection. They are used for numerous scour and erosion control projects worldwide – as a temporary or permanent solution. They are also an ideal emergency scour control product.

Are they effective for beach erosion control?

Yes. Rock  Bags are the perfect solution for beach and coastal erosion control. They have been independently tested at UNSW Water Research laboratory to determine their efficacy, and the results showed it as a huge success. Rock Bags adapt well to coastal ecosystems, supporting vegetating growth and marine life.

Are Rock Bags suitable for ports and wharf protection?

Yes. Rock Bags do a great job in protecting coastal and marine structures from scouring. You can use them for ports and wharves to prevent scouring from wave action and bow thrusters in ships.

Can I use them for bridge pylons and embankments?

Yes. Rock Bags were first used for the protection of bridge pylons. They offer a high level of scour protection compared to other methods like riprap – which has the potential to aggravate scouring. 

Unlike loose rock, the Rock Bags hold the rocks together and don’t let the sediment in the gaps be washed away. You can also use them to protect bridge abutments, embankments, riverbeds, rail beds, river banks, and more.

What are the other uses of Rock Bags?

Although Rock Bags are primarily known for erosion and scour control, they also have many other uses and applications. You can use Rock Bags to protect underwater cables and pipelines, build temporary work platforms, construct coffer dams, level uneven seabeds, and more!

Can I use Rock Bags as an alternative for gabions or riprap?

Yes. They are a great alternative for gabions or riprap. In many cases, Rock Bags are more effective because they are eco-friendly, long-lasting, and versatile.

What makes a rock bag different from a gabion?

A rock bag’s structure is flexible because it is made from a strong, netted fabric bag. 

Gabions are wired mesh baskets filled with rocks, concrete pieces, or similar materials. They are rigid in structure and which may make them limited in application.  Rock Bags are also easier to install and eco-friendly.

Are there successful cases of using Rock Bags for scouring and erosion control?

Yes. Rock Bags are a globally-recognised, successful erosion control product. They have been used for numerous civil engineering projects worldwide. You can read about successful cases of erosion control using Rock Bags under the “Projects” section on our website. 

Who do you supply Rock Bags for?

We primarily provide Rock Bags for projects done by private and public-sector companies. Local governments, urban councils, construction companies, civil engineering companies, and state sector corporations are some of our major clients. 

If you’d like to find out more and give your project a fresh start, get in touch with us through our site’s contact form. You can also call +61 2 9091 0360, or email 

Rock Bags