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Frequently Asked Questions

Our Flex MSE Frequently Asked Questions (FAQ's) page, provides a comprehensive list of anticipated queries and questions from do's and dont's to best practises.

Flex MSE® FAQs

Any technical information provided in relation to any product (whether before or after order) is provided by way of guidance only and, to the fullest extent permitted by law, without liability on the part of Gravitas International, for any loss or damage suffered as a result of relying upon it.

What is the size and weight of a flex MSE Bag?

A 'spec' vegetative medium filled Flex MSE Bag weighs approximately 32kg and is therefore a 2-person lift

Can Flex MSE be used on Sites of Special Scientific Interest (SSSI's)?

Yes. In 2016 the Environment Agency completed a case study using Flex MSE at Tadburn Lake. As Flex MSE didn't compromise and of the regulations, it was then approved for use on SSSI's throughout the UK and, to-date, is the only man-made retaining wall system to have received this approval, as far as we're aware.

How much maintenance will a Flex MSE wall need?

We offer vegetation mixes to suit every maintenance level, catering from zero maintenance installations to those tended to regularly.

How does Flex MSE compare to other retaining walls?

Flex MSE is longer lasting, more environmentally friendly and easier to install than other retaining wall systems. In addition, compared with concrete or gabions, Flex MSE typically offers up to 40% savings

Does the BBA approve the Flex Mse System?

Yes, Flex MSE has received BBA HAPAS approval for use with or without geogrids.

Will the Flex MSE system degrade?

Flex MSE won't break down or degrade over the 120yr design life. The system is inert, meaning that it won't react to PH levels, or release micro-plastics or fibers into the environment.

Can Flex MSE be used in watercourses?

Absolutely. The 120yr design life and 75yr warranty are the same for water or inland installations. Flex MSE has also been approved for use on all HS2 waterways by the Environment Agency and HS2.

Do you offer formal designs for the Flex MSE System?

Yes, please speak with our Technical team for more information

How much will my Flex MSE wall Cost?

Typically Flex MSE costs �200-�350/m2 to fill, deliver, install and vegetate within the UK or Ireland

What are the Vegetation options?

Any vegetation with a good root system will thrive with Flex MSE. Plants ranging from low/zero maintenance grass to willow trees have been installed and Gravitas International will happily provide site specific vegetation recommendations, depending on desired maintenance schedules, overall aesthetic and budget.

Can i put fencing above the wall of a FLEX MSE System?

Yes, absolutely. Loading, whether it's a fence, building, railway or highway can be built just 300mm from the face.

What are the dimensions of a Flex MSE Plate?

285mm x 99mm

Does the Flex MSE System has a maximum build height?

No, Flex MSE can be buiilt to any height.

What are the dimensions of a Flex MSE Bag?

760mm x 300mm x 140mm

How much does Flex MSE cost compared to other systems?

Flex MSE averages at 60% of the cost of hard armour systems and has lower repair and maintenance costs.

Are the bags pre-filled?

Typically, Flex MSE is prefilled before delivery to site. This halves the labour required and is therefore often the most cost effective method. In instances where the client would prefer to fill the units themselves, Gravitas will assess the site won material and provide a free fill-jig design.

What foundations does Flex MSE require

Flex MSE typically only requires a 300mm x 300mm trench foundation. It is filled with 150mm of gravel, then a single layer of plates and bags. Because Flex MSE is 100% concrete-free, there is no drying time to consider, making it much quicker and less invasive to install.

What type of reinforcement do you use when building a Flex MSE wall?

Any Flex MSE structure with loading and/or exceeding 1.2m high typically has an intgrated reinforcement system. Reinforcements include geogrid, earth anchors or rock anchoring. For walls under 1.2m high and without loading, Flex MSE Units can be installed using a Flemish Bond formation.Where Geogrid is required, we typically see it specified at lengths embedded into the backfill to 80% of the wall height and spaced every two/three layers of Bags.Reinforcement lengths and elevations may need to change depending on soils, surcharge, or other site conditions and the Gravitas International team will be delighted to provide design assistance.

What range of angles (slope / batter) you can create with Flex MSE?

Flex MSE can be installed from Horizontal (channel cladding, outfalls, etc.) to Vertical (as a living wall attached to existing structures). Typically, for retaining walls, up to 85� is recommended with the same two components.Thanks to the interlocking soft-armour capabilities, it�s simple to integrate different angles into the same structure. Natural, curved designs are easy with Flex MSE.

How do i vegetate my Flex MSE Installation?

There are several ways to plant a Flex MSE installation. Hydroseeding (spraying seeds and mulch onto the wall face) is the most common method because it covers a large area quickly and inexpensively. Gravitas International will be delighted to arrange for hydroseeding, or else coordinate our efforts with a hydroseeder or your choosing.Flex MSE can also be live planted with native groundcover plugs directly into the bag. Alterenatively, laying mature plants between bags as you build also gives great results.Often, a combination of methods are used to create the desired effect.

What goes into a Flex MSE Bag?

Sand and compost at a 70/30 ratio by volume is typical for above-water units. Those installed under water are usually filled with gravel, as they won't be expected to vegetate.

Does Flex MSE require skilled labour to install?

Not at all. Gravitas International provides FREE on-site training to ensure that every single installation is built to manufacturer's best practice. We can also provide access to a free, online installer's test, which, once passed will certify anyone as a registered installer.

What is FLEX MSE?

Flex MSE is a revolutionary retaining wall and acoustic barrier system consisting of two components, the Flex MSE Bag and Patented Interlocking Plate.  These leverage existing advanced soft armour systems to create an even stronger solution. Soft armour segmental systems allow for construction of permanent slope, wall and shoreline protection installations while allowing for full vegetation of the wall face. No concrete, no rebar, no forming, and often no levelling pad are needed.Flex MSE improves on other systems by offering greater geogrid compatibility and increased contact friction between the geotextile Bags.

HydroSack® & HydroSnake® FAQs

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How do I dispose of HydroSack®s / HydroSnake®s after the flooding has subsided?

To dispose of a HydroSack®️ / HydroSnake®️, simply split the outer bag and the contents can be poured into the ground, and will degrade in a matter of weeks. Ecological studies have shown that the contents pose no negative risk to the environment or wildlife.

Can they HydroSack® / HydroSnake® be reused i.e. will they dry out and return to their original state?

Both the HydroSack®️ and HydroSnake®️ will stay effective for 3-6months in situ once fully activated. After this time the product will require disposal. The inner contents of the HydroSack®️/HydroSnake®️ are degradable (to make them safe and easy to dispose of) so cannot return to their original state and be reused.

Can I lay them down dry to be activated by flood-water, and will they still be just as effective as a barrier?

We would always recommend activating them before laying them in place as:

  1. The HydroSack®s/HydroSnake®s weigh very little before saturation with water, so may move out of position if left dry
  2. If activated by flood-water, they are more dangerous to handle/dispose of than those activated by fresh water from a tap/hose as flood-water can be heavily contaminated.
  3. If stacking a flood barrier with multiple layers, the HydroSack®s/HydroSnake®s may not swell to their full size if left to absorb only flood-water
How do I inflate/activate a HydroSack®️ / HydroSnake®️?

The quickest way to fully activate HydroSack®s / HydroSnake®s is to soak them in water using a bucket or tub of water and this will take 2-3 mins per unit. They can also be activated by spraying with a hose, or pouring water onto them, but will take slightly longer than soaking.

How long can they be stored before use?

5+ years if stored in their original packaging and kept dry.

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