Specifying Gravel Stabilisation Grids SPECIFYING NIDAGRAVEL 129, 130 & 140 GRAVEL STABILISATION GRIDS

Choose the right Nidagravel honeycomb gravel grid for your next gravel stabilisation project
When it comes to specifying landscaping and construction products for external works, we understand it's important that architects, landscape architects, garden designers and specifiers have confidence in the products they specify. Our range of Nidagravel gravel stabilisers are manufactured to the highest standards by Nidaplast Honeycombs, the pioneers and world leaders in the production of plastic cellular gravel retention grids. With strict quality control standards and compression testing of every batch produced our gravel stabilisation system is quite literally tried and tested for every gravel stabilisation application to provide a long-term, stable, high-performance gravel surface that is 100% rainwater permeable over the entire surface area. In addition to the highly effective stabilisation of gravel paths, driveways and car parks - one of the main benefits of a porous Nidagravel grid surface is that it provides an excellent infiltration layer that will effectively reduce rainwater run-off and can be incorporated into any SuDS system or site drainage plan. The Nidagravel range of honeycomb gravel stabilisers includes three different products, these are Nidagravel 129, 130 & 140. Each product in the range will stabilise gravel effectively and each product is suitable for multiple applications. The area of the gravel surface, loading and intended use of your gravel surface will ultimately determine the choice of product. All our gravel reinforcement grids can be used for small and large projects, both residential and commercial as all the products in the range offer different benefits dependant on the layout, installation and application.

Summary of Nidgravel gravel grid applications
Our multi-purpose gravel grids can be specified for a wide range of gravel retention applications.
  • Nidagravel 129 - Pathways, patios and small driveways
  • Nidagravel 130 - Medium to large driveways, patios & pathways
  • Nidagravel 140 - Medium to large driveways, car parks & public spaces

  • Specifying the size of decorative gravel for filling Nidagravel honeycomb grids
    Nidagravel gravel reinforcement grids can be filled with a wide variety of decorative aggregates including various gravels and chippings. For Nidagravel 129 and 130 honeycomb grids, we recommend using a hard, angular decorative aggregate with a maximum size of 10 - 12mm in diameter. For our Nidagravel 140 gravel trays which are 40mm deep and our most robust grid, the maximum recommended size of gravel can be up to 18 - 20mm. The smallest size gravel we recommended across the range is 6mm. There are two main reasons for the gravel fill specification, firstly these aggregate sizes settle and compact well into the individual 49mm diameter hexagonal cells providing a solid, stable platform. Secondly, the gravel stabilisation grids are designed to be hidden and this size of aggregate allows for a 15 - 25mm surface layer of aggregate to cover the grids ensuring they are completely unseen. The finished surface dressing also helps distribute the turning forces applied to the surface by vehicles manoeuvring to ensure the optimum performance and lifespan of the gravel stabiliser.

    Summary of gravel size recommendations
    The minimum recommended gravel size across the range is approx. 4 - 6mm.
    For optimum stability of the gravel surface use angular shaped decorative gravel and chippings.
  • Nidagravel 129 - Maximum recommend gravel size 10 - 12mm
  • Nidagravel 130 - Maximum recommend gravel size 10 - 12mm
  • Nidagravel 140 - Maximum recommend gravel size 18 - 20mm

  • Specifying the sub-base material and build-up layers
    A standard granular sub-base specification is recommended for the installation of Nidagravel gravel stabilisation grids. The sub-base for a Nidagravel grid driveway is no different to that used for a standard block paved or tarmac driveway surface. An assessment of the sub-grade should be made to help determine the thickness of the sub-base and the surface of the sub-grade material should also be left firm, and graded to the required site levels during excavations. Nidagravel grids do not replace any part of the sub-base and are designed to stabilise the gravel surface only. The honeycomb cell structure of Nidagravel 129, 130 and 140 grids reinforce the gravel infill and transfer loads imposed on the surface directly to the sub-base, distributing them over a wider area. Nidagravel gravel reinforcement grids have very high compressive strengths when filled with gravel, from 300 to 400 tonnes per sqm depending on the product. This high compressive strength allows the products to be specified for a range of applications including driveways and car parks. Our gravel retention grids are also 100% rainwater permeable so they can also be used as an infiltration layer and combined with a Sustainable Urban Drainage Systems (SuDS). Subject to the drainage requirements of the project, Nidagravel grids can be laid over a permeable sub-base. The typical sub-base build-up for a residential driveway in the UK is a layer of membrane laid over the sub-grade to act as a ground stabiliser and separation layer, followed by approx. 150mm thick layer of Type 1 MOT 40mm down, which is laid down and compacted in two 75mm thick layers to achieve maximum compaction. The surface of the sub-base is then graded to the site levels with a tolerance of +/- 20mm and blinded with a 10 - 15mm layer of sharp or grit sand and compacted. The sub-base is then ready for the Nidagravel stabilisation grids to be installed and they are laid directly on top.

    Summary of sub-base specifications
    The following sub-base depths assume average ground conditions.
    An optional geotextile membrane can be laid beneath the sub-base for additional ground stabilisation.
  • Garden paths - Approx. 50 - 100mm compacted Type 1 MOT or similar sub-base material
  • Garden patios - Approx. 100mm compacted Type 1 MOT or similar sub-base material
  • Driveways - Approx. 150 - 200mm compacted Type 1 MOT or similar sub-base material
  • Car parks - Approx. 250 - 300mm compacted Type 1 MOT or similar sub-base material
  • Pedestrian public spaces - Approx. 150 - 250mm compacted Type 1 MOT or similar sub-base material

  • Specifying the installation of Nidagravel grids.
    All Nidagravel stabilisers are designed to be laid on top of the appropriate sub-base for the application and loading. A 10mm - 15mm layer of sharp or grit sand should be used to blind the surface of the sub-base and provide a thin bedding layer for the sheets. Nidagravel 129, 130 and 140 honeycomb gravel stabilisers have an overlap of membrane along one short edge and one long edge. Once the first sheet is laid these overlaps of membrane are folded out and the next sheet is placed on top and butted up to the previous sheet. No mechanical fixings are required as the weight of the gravel fill is more than sufficient to hold the sheets in place. We recommend laying full sheets across the flow of traffic in a stretcher bond pattern to stagger the joints, but where the site does not permit or it is not economical to do so, other layouts can be used without detrimental effect. Where possible full sheet sizes should always be used in high use areas, such the entry to a driveway. Offcuts can be utilised, to minimise wastage on-site, but these should be kept to a reasonable minimum size and be used towards the edge of low use areas. The honeycomb sheets can be cut to fit any shape required including curves and acute angles. It is best to cut Nidagravel gravel grids using an electric angle grinder or petrol cut off saw for a clean cut. Standard cutting discs can be used including diamond grit masonry discs. Sheets can also be cut with a fine-toothed handsaw. It is important to note that Nidagravel grids achieve their full load-bearing strength when filled with gravel and no heavy mobile loads should be moved onto the grids until an area is filled with gravel.

    Specifying the type of gravel and how to fill the honeycomb gravel grids.
    We recommend using any type of decorative aggregate with an average size of 10mm to fill Nidagravel 129, 130 and 140 gravel grids. A single size 10mm gravel can be specified or a graded decorative aggregate with a range of 4mm - 12mm in size. Nidagravel 140 can be filled with gravel up to 20mm in size but no larger. There are several reasons for these specifications, firstly this size of gravel fills the 49mm diameter honeycombs cells completely and compacts well within the cells with minimal voids. The compacted gravel within the honeycomb cells gives the Nidagravel stabilizers their full load-bearing capacity, which is 300 to 400 tonnes per sqm depending on the product used. Any angular 4 - 20mm decorative aggregate that is supplied in the UK either in bulk bags or loose loads can be used to fill Nidagravel grids. It is generally acknowledged that the characteristics of more angular gravels or decorative chippings will compact and interlock better than more rounded gravels. Due to their shape, the individual pieces of angular aggregate, naturally interlock well and when combined with Nidagravel grids provide maximum surface stability. The use of a harder stone or gravel such as flint, granite, basalt, quartz or hard limestone rather than a softer, calciferous stone ensures the longevity of the gravel fill, this is more important when specifying the gravel type for a gravel driveway or car park due to the loads imposed. Nidagravel gravel trays are designed to be an invisible gravel stabiliser and to achieve this, during installation, the grids should be overfilled by approx 25mm of gravel. This can only be achieved by using the gravel sizes recommended. Approximately 2 - 3 weeks after installation the gravel overfill will have naturally settled into the honeycomb cells and have been compacted by vehicle and pedestrian use to leave approx 10mm - 20mm surface layer of gravel depending on the gravel size used. This settlement/compaction process can be speeded up by lightly compacting the gravel overfill with a medium to lightweight plate compactor or garden roller at the end of the installation, although this is not a requirement for a professional installation. After 2 - 3 weeks, the gravel surface should be visually inspected and if the Nidagravel grids are showing through in any areas, these need to be topped off with additional gravel. It is important to maintain an even 25mm overfill of gravel when filling the grids so that the surface layer settles uniformly at the same rate. When it comes to filling Nidagravel grids with gravel, an initial area should be filled with gravel and working off this area the rest of the grids can be filled. Always work on a filled section of grids as it is not until the grids are filled that they achieve their full compressive strength. Do not take heavy loads onto the empty Nidagravel trays. Depending on the size of the project Nidagravel grids can be filled by hand using a wheelbarrow or machine filled using an excavator working off a filled section of grids. When taking delivery of large volumes of gravel on-site, 10 - 20 tonne loose loads delivered by 8-wheeler tippers can be poured directly on top of the grids ready for spreading. The delivery vehicle should reverse up to the edge of the grids, slowly tip 2 - 3 tonnes of gravel onto the grids in a controlled manner to load a section of grids and then the rest of the load can be tipped. This ensures there is no movement or damage to the gravel grids. With large projects and deliveries of loose loads of gravel, machine fill is the quickest method.

    Specifying the maintenance routine for stabilised gravel surfaces.
    This is a simple area to specify as the product range requires very little maintenance after installation. We would recommend that in addition to standard maintenance of external surfaces that a 6 monthly inspection of the surface is carried out to ensure that the honeycomb cells of Nidagravel 129, 130 and 140 are covered with a 10 - 20mm layer of gravel. This simple visual inspection is quick to complete and where necessary more gravel can be added and levelled as required to maintain the surface layer.

    Nidagravel UK - Making gravel surfaces perform better...