Installation Guide and Specification Notes for Artificial Grass
The following guide-lines are intended to be modified having due regard to the site being prepared for use as an artificial lawn, and are the minimum required for an installation. Areas that were previously used as natural grass lawns should require less preparation than those that were previously flower borders, vegetable gardens or cleared scrubland, as these areas may have had soft ground or old roots that will decay over time.
Sandy soil may be free draining, shallow soil over chalk may be subject to frost heave, and clay ground will be prone to shrinkage and heave during dry or wet conditions, and it is important that consideration is given to the site subject to the project, and not simply treated as being a generic part of the scheme. All sites should be treated as bespoke.
Having cleared the site, and removed all vegetation including grass sward, excavate to running levels and falls to a depth of not less than 75mm – preferably 100mm – below the proposed finished levels of the project.
Apply a pre-emergent weedkiller if required and approved by the client.
Consolidate the ground by treading the area using stout boot heels, by compacting with a vibrating mechanical plate, (NB It may require a light dressing of MOT on top of the soil to allow the machine to move across the ground), or vibrating roller.
Any soft areas should be levelled out using MOT and not soil.
Any areas, or soil types that may be considered to retain water, or on certain sites where flooding may be a risk, it is advisable to instal a drainage system under the sub-base. These may be shingle filled French drains, perforated pipes or a combination of both. Ensure these drains are protected with non-woven geotextile membranes to prevent blockage through silt build-up.
Once the site has been fully prepared, an edging should be installed around all sides of the proposed site (see cross sectional diagrams) either in Grade 4 treated timber, metal, composite boards or concrete, to form a solid, firm edge around the project footprint. (NB If using a raised edge e.g. timber ‘sleepers’ to retain the site, ensure they are very firmly fixed to the ground, otherwise they will ‘spread’ during the compacting operations. Care should be taken to ensure that the sub-base materials cannot migrate from underneath the timbers, otherwise the edges may subside due to soft areas.
Once firmly consolidated, cover the area with a sheet of non-woven geotextile membrane, taking care to overlap the final site footprint.
Spread and lay two layers of MOT Type 1, 40 – 50mm each layer, to a total of 85mm – 100mm (minimum 75mm) across the area. Ensure a smooth finish to running levels and fall, topping up any low spots with additional MOT. See notes below reference MOT Type 3 when used for pet friendly, or sites requiring additional drainage.
Spread a layer of 15 – 20mm (maximum 25mm) of Granodust over the surface of the site, carefully grading and levelling to running falls as required by the design.
Once fully compacted, cover the whole area with a second sheet of non-woven geotextile membrane, taking care to overlap the final site footprint.
In some areas, it may be necessary to instal shock pads to the underside of the grass matting. These may include children’s play areas over hard ground. This matter will be subject to the quality, density and pile depth of the selected matting.
Carefully position the roll/s of artificial grass, ensuring that all sections are facing in one direction as they are introduced to site. This is to ensure the pile is facing in the same direction (preference will be to face the pile towards the main view/ house). Carefully unroll the mats, allowing overlaps at all sides. Position the rolls close together in preparation for joining (if required).
Allow the grass to ‘settle’ for at least two or three hours, depending on the temperature, to allow any creases to drop out and the pile to relax until the joining stage (if any) is required. Alternatively, use carpet knee kickers to ensure the matting is taut, eradicating any ripples within the area.
Carefully join the grass matting rolls together, using one of several techniques. All will require the leading edge of the matting to be prepared by carefully cutting the outer four stitches of the base back from the roll edge by four stitches. Always make the cut from the back, following the line of the backing material. This is essential to ensure that the pile may be dressed into a straight line and allow for marrying the ‘stalks’ and pile together, neighbour into neighbour.
Techniques include securing the matting using metal staples or hoops, teasing the two edges together using six-inch nails as micro-levers to pull both sides close together. Once satisfied with the positioning, push the staple into the ground, carefully lifting any trapped stalks before finally pushing home.
Other techniques involve the use of either adhesive seaming tape or a joining tape, which is laid underneath the two rolls, and adhesive is spread on the tape before bringing both surfaces together. Care should be taken to avoid getting any adhesive on the grass stalks, as this will be difficult to remove or disguise.
Variations in securing techniques may vary from firm to firm, taking into consideration the depth of pile and weight of the matting, together with site conditions.
When using adhesives, leave the joined matting for at least 24 hours before walking over the seams.
Depending on the selection of grass matting, some may benefit from a surface dressing of kiln dried sand. This is applied at a rate of 2kg – 5kg m2 to either aid with the weighting down and securing of the matting, or to assist in holding the grass stalks or pile to ‘lift’ and remain upright. This will help to reduce static on the lawn, and act as a coolant in hot weather. However, sand may harbour weed seeds, hold pet urine smells and get into eyes of animals and children. Volcanic ash may be used instead of sand.
Once the matting has been installed, joined and settled, any excess should be trimmed off using a sharp knife, carefully cutting from the underside, by turning the matting over and trimming to suit. Once trimmed, the edges may be secured using adhesive (on concrete edging) or stainless steel screws/nails/staples (18-25mm) into timber, or screws into composite @ 30 cm centres.
Once the matting has been firmly fixed at all points, it may be brushed using a stiff broom or mechanical brush, ensuring the strokes are made in one direction to provide the matting with a uniform appearance, or striped to replicate a mown lawn (see page 11).
When using MOT Type 3 as a sub-base, due to the fact that the material is not as readily compacted (as MOT Type 1), a deeper sub-base is required. 125mm of MOT Type 3, topped with 25mm of 3 – 6mm aggregate, covered in non-woven geotextile membrane laid ON TOP of the aggregate and UNDER the 15mm Grano-dust layer. This is essential to prevent the fine Grano-dust from migrating into any voids in the MOT Type 3.
Laying artificial grass over concrete is a similar operation in many respects, except the requirement to consolidate the ground before laying. Thoroughly clean the area, brushing and washing away all dust and grime, otherwise any detritus will prevent adhesion between the matting and surface. All oil, grease, tar etc to be removed using recommended suitable products. Jointing should be by seaming or joining tape, as described above. (NB Some adhesives require a dry surface before jointing, whilst others may be used in wet conditions. See manufacturers notes.)
The matting must be glued down using strips of adhesive, running in thin lines along the length and width of the matting, ensuring that the ‘rows’ have gaps in between to prevent rainwater from building up in the pile.
Laying over tarmac/tennis courts may require the installation of a weed suppressant non-woven geotextile membrane. Both layers will need to be firmly glued down, with care taken to ensure the edges are completely fixed to prevent wind from getting under the materials.
(If using shock pads to provide some softness under the grass matting, ensure that the pads are securely fixed to the concrete/tarmac, otherwise they will become a weak point allowing separation of the layers. The bond is only as strong as the weakest material or surface).
Notes
If working on a known size of lawn – a five metre circle for instance – remember that the size of matting will be reduced, allowing for the trimming of the base for joining purposes. If using a two metre wide roll and a three metre roll to cover five metres, there will be a shortfall of 10cm for trimming. It may be advisable to design a circle of 4.9 metres rather than 5.0m
In some instances, complaints have been raised regarding overheating of artificial grass lawns. Although not common, it is a subject that should be raised and discussed with the client to ensure they fully understand and accept that heat may be a problem.
Whilst the majority of grasses are UV warrantied against fading for ten years, be aware that certain objects – mirrors, stainless steel statues, glass windows etc, may have a specific and detrimental effect on the matting, in some cases, scorching/ melting and fading the grass pile. (It is worthwhile considering mentioning this factor during the design or tendering stages of a scheme.)
Certain garden features that produce heat – firepits, barbecues etc, should not be used on or near to artificial grass installations.
Some firms offer a bespoke repair service for damaged lawns. It is always advisable to keep any sizeable off-cuts as repair spares in the event of such damage.
How Not to Secure the Edges of Grass Mat
The use of a non-treated timber batten designed for use on a roof, demonstrates the necessity of constructing a strong edge. Secured only with a 100mm nail pushed into the sharp sand at 1.0m centres, the batten is easily lifted. In this image, the grass matting was cut too short for the area, and an additional strip 50mm wide was screwed onto the batten, leaving the whole side/flank edge of the lawn unsecured.
Moreover, the concrete block edge to the paving was not secure, laid over MOT Type 1 with no concrete or mortar haunching to prevent migration.
Concrete Edged Lawn – Layered Cross-section
The use of concrete as a lawn edging is versatile, allowing for curves and bends to be formed simply by temporary shuttering (even thin ply may be used), securely fixed into position with short lengths of reinforcing bar to create free-flow and bespoke designs.
The inclusion of reinforcing bars, whilst not essential, add to the strength of the edging in case of clay ground. The concrete should be laid ‘wet’ with a strength of at least one part cement to five parts sandy ballast.
Once hardened, a vibrating compactor plate may be used to ensure a solid foundation of MOT Type 1 for the matting, reducing the possibility of settlement against a weaker edging.
Timber Edged Lawn – Layered Cross-section
The use of timber as an edging material to contain and support the sub-base and laying base of the AG matting is commonly installed. Ensure that the wood is Class 4 to prevent rotting after a few years.
Timber sizes can vary from 50mm x 100mm as shown in the diagram, although 50mm x 75mm may be considered adequate.
Composite ‘timber’ may be used instead, offering a much longer lifetime.
Edging must be firmly secure, using 50mm x 50mm x 450mm Class 4 wooden pegs, or composite pegs fixed into the vertical boards. These may be non-ferrous screws, or stapled with 18 – 25mm staples using a staple gun.
Steel or alloy metals may be used instead, and the grass matting secured by means of adhesive instead of screws or staples.
Treatment of Recessed Inspection Covers
In order to compact the MOT sub-base without risking damage to an inspection cover, the use of concrete as a surround will enable the base material to be adequately compacted using a vibrating compactor plate.
Temporary timber edging may be removed after hardening, and the grass matting secured with adhesive.
Infilling the recessed manhole cover with strong wet concrete, taking care not to fill the lifting key holes, to the same level as the outer surround will ensure an invisible joint to be made, as though joining the material without using a joining tape.
Free-draining Sub-base for Pet Lawns
Following the same principle as the Timber Edged detail, the use of MOT Type 3 is recommended for use where large pets are present, to ensure a free draining sub-base.
MOT Type 3 is more open in nature than MOT Type 1, and may not be so easily compacted. This is essential to allow water to pass through more freely, and requires extra depth of material. 125mm may be considered adequate, according to the site.
Note that the upper membrane has moved to UNDER the laying course, with a layer of 3-6mm crushed stone covering the MOT Type 3 to prevent the fine material from migrating into the open and porous sub-base.
Finally, top with grano-dust 6mm to dust and lay the AG matting in the usual manner, either with adhesive or screws/staples.
