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Appropriate Base Materials for Artificial Grass Lawn and Landscape Projects

Appropriate Base Materials for Artificial Grass Lawn and Landscape Projects

crowned artificial grass lawn low traffic

Low Traffic Installation of Artificial Grass - Crowned away from driveway

Artificial Grass – Lawns & Landscape

AGGREGATE BASE COURSE

Aggregate is the largest single material used in construction and its properties are highly valued as the foundation of all quality pavement, paver, aphalt and other traditionally hard and new porous materials surface projects.

Compactable aggregates are also commonly used as base materials under artificial grass and synthetic turf systems as they impart the same important stabilizing qualities to these solutions, as well.


There are many uses for artificial grass and synthetic turf and it is important to understand the site’s soil conditions and its intended use!

Under ideal conditions – you may only use 2-3 inches of base and under the poorest conditions base specifications may include additional excavation and the use of not only several types of base and fabric layers for stability and long-term percolation, it may include the use of minor to extreme drainage systems, as well.

Appropriate base specifications for other uses must consider stability, drainage AND uses such as sports field safety and ball performance, daycare fall zone safety, ADA compliance; for leisure sports and play areas we also need to keep in mind performance [target greens, bocce and other sports], to extreme traffic or weight-load. Each USE may require different base considerations and are not discussed here.

As the material used to replace native and amended soils in the artificial grass system solution – the selection of the appropriate aggregate mixture is critical to match to 1. use, 2. traffic and 3. weight-load requirements while considering A. weather and B. watershed & drainage needs.

To insure high rate of long-term permeability and dimentional stability is the center of an artificial grass system’s design.

The stability of an unbound granular base course comes mainly from particle interlock [bridging or grain-tograin] and surface friction during installation. The gradation (variation) of particle size distribution is therefore an important characteristic for strength and long-term permability.

Given any amount of space to fill – water will fall down with gravity. It is our job to understand the weight-load, watershed requirements and soil conditions of our site and plan for the excavation and import of proper materials to either 1. maintain existing conditons or 2. improve upon them.

Under artificial grass surfaces, course aggregates percolate differently that if rain water was pounding on it from the top. The SYSTEM of a permeable artificial grass fabric and appropriate infill component actually serve as a buffer, holding water, under head-pressure, above the road base, allowing it to flow vertically into the road base and then, down into the native soils or into various drainage solutions that could be specificied for the project.

If the material and fines are too small – or even if properly sized but compacted too tightly – the permeability will suffer and the materials may harden; which can lead to cracking [especially in environments where soils heave due to dramatic changes in weather temperatures or rain/snow fall].

To keep it simple – optimum materials for use under most landscape or lawn artificial grass surfaces will have a 70-30 ratio of solid mass to fines; fines will be granular materials with low leves of clay, lime, etc. Materials should be “new” and not reclaimed or repurposed and should display a clumping action when a handful is taken from the pile. Water content of your base materials can be adjusted by adding during installation [fine mist or spray nozzel is recommended] or reduced; by leaving materials to “drain out” or dry.

compactable-aggregate-illustration

a. Aggregates with no fines b. Aggregate with sufficient fines c. Aggregate with great amount of fines (Yoder and Witczak, 1975)

a. Aggregates with no fines
b. Aggregate with sufficient fines
c. Aggregate with great amount of fines
(Yoder and Witczak, 1975)

=======================================================

A. is a mix of simply cleaned crushed stone. If installed properly, as base, alone, under artificial grass surfaces, it provides the highest permability, however, can leave the surfaces looking [bumpy] unlevel, and may move under the artificial grass surfaces under heavy weight or traffic patterns.

These materials, along with granulated silicas and clean lava can be used, under certain conditions, as base – however – even a minimum amount of traffic over these materials – MAY lead to continued
compaction, material degradation and project surface levels could start to rut, creating depressed areas, under the surfaces.

When using these types of materials, it is critical to add exterior perimeters around the entire site [hard walls, commonly called "nail rails" in sports field installations - a variety of products can be used - various flexboard [ie: EPIC(r)] , block, brick, etc to provide a hard edge, thus creating a “basin” in which to compact materials – we recommend starting with a primary layer of fabric, under these loose materials, to insure the materials do not creep or combine with native soils.

B1: is an ideal mix of larger, 60-70% crushed hard stone (3/8 to 3/4 inch crushed, clean granite is preferred) and 40-30% of mass of fines (materials that range in size from dust to 1/8th or 1/4 inch). These fines are the materials that will help with compaction and provide a smooth top grade under artificial grass surfaces as you also achieve the proper density so that the materials have an adequate “grain-to-grain” contact [aka bridging].

After proper compaction* for most lawn or landscape projects of approximately 75-85% Proctor your lawn should appear natural, in grade, roll or undulation. You can easily achieve this level of compaction by simply using a water filled roller. Do NOT over compact base – this will reduce permablility.

B2: ALTERNATIVE: mixes of 60-70% large crushed and 40-30% silica can also be used – provided angular materials are specified and you can achieve the proper density so that the materials have an adequate “grain-to-grain” contact [aka bridging] – the materials can compact and provide an adequate base for heavy traffic areas, in extreme watershed conditions.

When using these types of materials, it is critical to add exterior perimeters around the entire site [hard walls, commonly called "nail rails" in sports field installations - a variety of products can be used - various flexboard [ie: EPIC(r)] , block, brick, etc to provide a hard edge, thus creating a “basin” in which to compact materials – we recommend starting with a primary layer of fabric, under these loose materials, to insure the materials do not creep or combine with native soils.

C: is an example where the material mix of solid to fines is out of proportion and you can easily see how the rocks will float in the fines making this a very unstable base. Heavy traffic, heavy weight loads and soil heaving will all impact this base material – ruts, poor permeability, changes in grade or level can all result.

Base Materials Selection for Artificial Grass Lawns & Turf

The most important aspects to keep in mind when considering a course compactable aggregate for artificial grass solutions are ratio of fines to size of large, unbound rocks and the quality of the materials. The larger, course materials should be installed no less than 3 inches or you will find that the materials are subject to shearing, poor compaction and lower weight-load capacity – especially during saturated damp conditions.

Commonly used course compactable materials would include NEW 5/8th or 3/4 Road Base with fines (aka Class II, AB, etc); OR some types of clean, reclaimed lava rock + crushed, and a manually mixed content of 1/4 to 3/4 clean crushed mixed with silica sand materials.

“Repurposed” or “Recycled” course aggregates with fines can have many surprises! Weed or grass seed, garbage, dirt and other contaminants like chunks of cement, asphalt or other building materials. These contaminants can create hard spots, obstruct the surface percolation, interfere with proper compaction and final grading.

The DENSER and SMALLER the course aggregate materials – the lower the sieve or percolation.
These types of base materials tend to continue to compact in locations with high rain or snow fall. This continued compaction will adjust the final grade of your site [it may begin to look like it's sinking], may affect the permeability and there-fore the stability of infill and performance of the surfaces. Because of it’s sieve, it can HOLD more water, LONGER, especially in wet-weather climates making a DG base a poor choice for heavy traffic or weight-loads. It is important to consider all these factors prior to selection of base.

DG or decomposed granite is a popular material and best used as a layer on the top of base, as described above; to smooth or change elevations on putting greens. It can be adequately used as a 3 inch base layer in very LOW moisture/rain/snow geography.

It is not recommended to install a larger lift than 4 inches of DG.  You can always use another base below a final layer of 2-3 inches of DG if you need to elevate above 3-4 inches to reach your final grade.

DG and other 1/4 (minus) aggregates are not recommended as the sole base solution for sites located in high rain/snow areas OR where soils may heave during the change of seasons. It is highly recommended to use a weed, rodent and pest abbatement fabric under all DG projects, if conditions suggest it’s use.

Continuing your investigation into base materials:

To further understand base specifications under more severe conditions of safety [sports fields], performance [target greens, bocce and other sports], to extreme traffic or weight-load, it is best to consult the Army Corp of Engineers for your area.  They can provide you with an excessive amount of data regarding watershed, soil type, density for your locality.

Other resources that can help you understand local conditions are your own county or city planning departments, HOA, CID or community contractor exchange or bureau.

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ASGi - the Association of Synthetic Grass Installers was founded in 2007 to help connect market partners and their customers in the artificial grass and synthetic turf industry. We have grown into a global presence, focused upon the niche markets of landscape and leisure sports. Take a moment, browse the site - or email or phone us if we can be of help in answering a question or locating information. Phone US TOLL FREE - 888-378-4581 View all posts by ASGi

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