Guide to Suitable Bases for Resin Bound Surfacing- Part 3

Grid Systems

Ground reinforcement systems also known as “grids or tiles” are a relative newcomer to the sub-base market but have been around for over 20 Years.

It is a type of permeable paving grid made from plastic that interlocks with other tiles and is used in the construction of car parks, driveways, patios and walkways.

Ecogrid, a leading manufacturer, produce a grid called the E40 XXL – it has a size of 100cm (1mtr) x 133cm (1.33mtrs). This results in fewer interlocking sections when compared to other smaller grids. The benefit is that you have less joint movement and a more stable base. It is advisable to also purchase the smaller E40 to minimise cuts and waste as it is a handy 33cm x 33cm. This will reduce waste at the edges of your installation by utilising the smaller grid size.  Additionally, Ecogrid produces tiles which are designed for the implementation of a curve and a slope making endless design options.  The grids are made from specially selected recycled plastics and Ecogrid claim to be carbon neutral. 

The popularity of this highly permeable and frost-safe grid system is high with over 1 million grids being used per year and often comes with a substantial warranty/product guarantee.

The grids have become increasingly popular as you do not need any heavy plant or skills for installation. The simplicity and portability make this an ideal solution for locations with restricted access.  The benefits can include less digging out, reduced labour costs and it is quick, clean, and easy to lay.

Whilst grids are available in a variety of depths and from differing manufacturers, for a resin bound system we recommend a grid with a depth of 40mm. The base would consist of MOT type 1 or 3  – 120- 150mm depth which is compacted with a vibrating plate (Whaka), followed by a non-woven geotextile membrane (permeable fabric) which is pinned into place. A layer of sharp sand or small aggregate grit is levelled at a depth of 10 – 20mm, this is used to bed the grids onto it and prevents them from moving.

The grids are then reinforced and stabilised with the addition of clean stone. Any strong angular aggregate can be used such as clean crushed concrete or limestone.  It needs to be an angular aggregate so that it locks together better.  Limestone is preferable as you get less thermal expansion, it’s widely available and is relatively cheap. The limestone needs to be between 4-16mm in size, once the grid is filled, it is compacted with a vibrating plate. You will need 0.081 tonnes of stone per m2 of grid. When the grids are filled and compacted it creates a very strong stable monolithic structure which can withstand temperatures of minus 50c to 90c. The strength of the system can take an axle loading of 20 tonnes or 400-800 tonnes per m2 (dependent on the stone fill and grid manufacturer).

As the limestone is just below the surface of the grid it is recommended that the resin bound system be applied at a depth of 20mm. The resin bound is applied in the same way as other sub-bases.

Permeable Base Mix “Advanced” Concrete

A relatively new product on the market that can be used as a suitable resin bound sub base is advanced concretes. These are often called a “permeable base mix” (PBM). The product consists of a structural lightweight 4-8mm rounded expanded clay aggregate and advanced cementitious-based blended binding agents. The United Kingdom has a few manufacturers of similar systems but we prefer the Maxrete offering. It comes in a lightweight, 40 Litre premixed bag and a pallet can hold 25 Bags which equals 1m3 and has a staggeringly low pallet weight of 625kgs. The system is designed to dissipate water at a very fast rate. Closer inspection will show that the system is very similar to the resin bound mixes as the rounded aggregates bond to each other creating a honeycomb structure. It is worth considering as a bespoke solution that is fully suds compliant (Sustainable Urban Drainage). The base mix can be used for both structural and non-structural applications. Maxrete, claim that the base mix, once installed is as strong as traditional concrete.   

Application depths vary dependent upon the expected loads.  For patios and walkways that will have pedestrian traffic the recommend laying depth is 50mm. For light cars and domestic drives, it is recommended that you lay at 75mm.  For heavier vehicles 4X4’s / horse Boxes / large vans then the depth is 100mm+.  The loading tolerance of the base mix is 15 tonnes, which is far greater than most campervans and 4x4s.  It is mixed and then applied to a layer of compacted MOT type 1 or type 3 at a depth of approx. 150mm, type 3 being preferable.

Coverage rates are impressive, a single 40-litre bag will give you 0.80m2 at a depth of 50mm, 0.53m2 at 75mm and 0.40m2 at a depth of 100mm.  Working out how many bags you need is a simple calculation.  The base mix is a little on the expensive side with prices of around £16.80 per bag and delivery charges.

The base mix has several significant benefits for both contractor and homeowner. Being so light it enables contractors to manually carry more in a van without exceeding loading limits. Ideal if you are working in a tight area that has restricted access. The system does not need expansion joints (very beneficial for the seamless driveway look) with very little if any thermal movement. It provides a frost-proof bedding layer and resists frost heave (an upwards swelling of soil during freezing conditions). The base mix is a very strong, high quality and durable sub-base solution with little or no maintenance. It is 50% lighter than concrete, making lifting and transporting easier, with the same volume and the same strength as traditional concrete.

The product is produced in accordance with EN1520 & BSEN13055

The mixing of the product is a simple process. Using a traditional belle cement mixer, you follow these simple steps:

• Step 1, Empty the contents of the 40 Litre Bag into the mixer (full bag).
• Step 2. Mix dry for 60 seconds, this ensures you get an even distribution of aggregate and additives.
• Step 3, Add 3 Litres of clean water and mix for 60 seconds.
• Step 4, Add another 3.5 Litres of water and mix for 90 seconds.
• Step 5, Empty the mixture onto the desired area.
• Step 6, Rake / spazzle out the mixture making it relatively level.
• Step 7, Screed back level (with wood or a bar) and then lightly trowel into place with relatively low compression.
• Step 8, Leave 2 – 3 Hours to harden into a stable mass that is not reactive in normal environments

The base mix is ready to walk in 24 Hours.

Please note whilst the system uses little water it is advisable to wait at least 24 hours before the application of the resin bound system. You MUST use Primer C before the application of the resin. This is simply rolled into place using a trough and decorators’ roller. Coverage from a 5 Litre tin is 40m2.