Frequently Asked Questions
What is G-Max?
G-Max is a measurement to determine the ability of a surface to attenuate impact forces. In an athletic environment, G-Max measures how much force (such as from a player’s head) is absorbed by and dissipated into the synthetic turf system as opposed to the player’s head.
G-Max is determined by a numerical value obtained from a G-Max testing apparatus. The higher the numerical value, the less an impact is attenuated into the impacted surface and, in turn, more is absorbed by the player’s head.
While properly maintained synthetic turf fields should exhibit A G-Max value below 145 (averaged over multiple test locations), fields exhibiting average G-Max values above 165 are generally deemed unsafe.
Why is G-Max misunderstood?
G-Max is not a static measurement. G-Max testing is typically done right after a field is installed, or after a field has been professionally groomed. Although the measurements at “that time” will often be low/safe, they are only representative of the shock attenuation conditions at that particular point in time. Indeed, the G-Max value will change over time and playing conditions. For example, as the infill material (I.e., the sand and rubber particles between the synthetic turf fibers) become compacted by such things as hours of play, maintenance and weather, G-Max values will become elevated.
How long will your synthetic field last?
The number of years a synthetic turf system will last is a function of the quality of the product and installation, the amount of use the field gets and how well the field is maintained.
Be aware of what you are buying! Although most synthetic turf products will "look good" after they are installed, noticeable differences in fiber and backing integrity, aesthetics and playability between high quality and low quality products will become apparent in as little as one year.
Properly maintained quality fields today should last at least 10-12 years.
What are slit-film and monofilament fibers?
Slit-Film fibers are tape-like flat strands that are extruded with vertical slits. If you pull the slit-film fibers apart, you will notice that the slits reveal a “honeycomb” type pattern. As the field is being installed, a grooming machine will actually break the fibers apart (“fibrillation”). Once fibrillated, each slit-film fibers will have the appearance of several individual fibers. Slit-film fibers are relatively soft, compared to other types of fibers, and, in turn, exhibit less infill splash than other fibers.
Monofilament fibers are extruded as single, individual blades that, without any fibrillation, resemble individual blades of grass. Monofilament fibers typically have geometries and chemical compositions that enable them to stand up straighter than slit-film fibers.
The above information is general in nature. There are many different variations and qualities of both slit-film and monofilament fibers. The higher the quality, the more durable the product, among other things.
What are the different types of synthetic turf products?
Synthetic turf products are typically constructed with all slit-film fibers, all monofilament fibers, a blend of both and, insome cases, with curly "texturized" fibers added in. In “conventional” synthetic turf, one or more fibers are stitched “tufted” through a backing material so that each fiber has two free ends extending above the backing material (so as to simulate the look of natural grass). The fibers are tufted into rows, and each row of fibers is spaced apart a set and consistent distance apart. Thereafter, the bottom of the backing (the portion that would not be exposed when the turf is installed), is coated with a urethane adhesive. The adhesive serves to mechanically secure the fibers in place.
When a synthetic turf product is made with a blend of monofilament and slit-film fibers, the tufting is done in one of two ways: 1. Both monofilament and slit-film fibers are tufted together so that each row of fibers comprises a blend of both types of fibers; or 2. Monofilament and slit-film fibers are tufted separately so as to create alternating rows of all monofilament and all slit-film fibers. This last type is less than ideal because the alternating rows look less natural and there is a greater propensity for the monofilament fibers to come loose over time. It is MWSTS’s opinion that an all monofilament product or a blended product with alternating rows be avoided unless the product is made through a “weaving” process as opposed to conventional tufting.
In addition to "tufted" products, a more recent trend has been to "weave" the same type of fibers as above, into and through a backing material. The backing material is often woven simultaneously with the weaving of the fibers -- creating a synthetic turf product that substantially precludes fiber loosining and loss over time.
What are the particles (“infill”) that go in between the fibers and what do they do?
The particles are typically a combination of sand and a resilient particle, such as rubber. Together, these particles provide, among other things, ballast to the overall system, helps maintain the synthetic fibers in a substantially upright orientationand helps to provide proper shock protection (from head injuries) as well as energy restitution.
What are the different infill materials?
Crumb Rubber: Crumb Rubber is derived from scrap car and truck tires that are ground up and recycled. Two types of crumb rubber infill exist: Ambient and Cryogenic. Together these make up the most widely used infill in the synthetic sports field and landscape market.
Coated Rubber Infill: Both ambient and cryogenic rubber can be coated with colorants, sealers, or anti-microbial substances if desired. Coated rubber provides additional aesthetic appeal, reduction of dust by products during the manufacturing process and complete encapsulation of the rubber particle. Coated rubber plays similar to non-coated rubber.
EPDM Infill: EPDM (Ethylene Propylene Diene Monomer) is a polymer elastomer with high resistance to abrasion and wear and will not change its solid form under high temperatures. Typical EPDM colors are green and tan. EPDM has proven its durability as an infill product in all types of climates. Its excellent elasticity properties and resistance to atmospheric and chemical agents provide a stable, high performance infill product.
Organic Infill: There are several organic infills available in the North American market, all utilizing different organic components, such as natural cork and/or ground fibers from the outside shell of the coconut. These products can be utilized in sports applications as well as for landscaping. At the end of its life cycle it can be recycled directly into the environment.
Sand (Silica) Infill: Pure silica sand is one of the original infilling materials utilized in synthetic turf. This product is a natural infill that is non-toxic, chemically stable and fracture resistant. Silica sand infills are typically tan, off-tan or white in color and - depending upon plant location – may be round or sub-round in particle shape. It can be used in conjunction with many other infills on the market to provide a safe and more realistic playing surface.
Coated Silica Sand Infill: This class of infill consists of coated, high-purity silica sand with either a soft or rigid coating specifically engineered for synthetic turf. These coatings are either elastomeric or acrylic in nature (non-toxic) and form a bond with the sand grain sealing it from bacteria to provide superior performance and durability over the life of a field. Coated sand is available in various sizes to meet the application’s needs.
TPE Infill: Thermo plastic elastomer (TPE) infill is non-toxic, heavy metal free, available in a variety of colors that resist fading, very long lasting, and 100% recyclable and reusable as infill when the field is replaced.
What is a shock pad?
A shock pad is a structural product that is engineered to allow for proper water drainage, as well as to maintain safe G-Max levels (shock attenuation) -- regardless of infill depths or infill compaction.
What goes under synthetic turf (“the base”) and what is its purpose?
Typically, the construction underneath a synthetic turf system comprises a stone base with both interior and perimeter drainage, among other things. In some cases, a "shock pad" is placed between the stone base and the bottom of the synthetic turf.
The stone base provides structural support for the synthetic turf and the shock pad is intended to provide an added safety net against head related injuries.
More details about the base construction and shock pads are explained in other parts of our FAQs
Does synthetic turf require maintenance?
In short, yes. In order to keep your synthetic turf looking and playing great, as well as to help increase its longevity, it's important that routine and common sense maintenance be implemented. This typically includes checking for any loose inlays (such as hash marks, numbers, arrows, etc), removal of surface debris and periodic sweeping and grooming of the field.
How is a typical base constructed in the Midwest?
Although the final base construction is dictated by many factors, including but not limited to soil conditions, storm water management requirements, stone cost, type and availability, etc., a typical base in the Midwest is constructed as follows:
- Excavation of natural surface until 95% compaction is obtained;
- Excavate for drainage trenches around perimeter of field;
- Install geotextile fabric;
- Install 8” – 24” collector pipes in trenches;
- Install 1” x 12” flat panel drains from center of field to collector pipes (typically 20’ on centers);
- Construct concrete curb around entire perimeter of field;
- Attach 2” x 4” treated wood or composite nailer boards to inside perimeter of concrete curb approximately 1.5” below top of curb;
- Compact and laser grade approximately 4” of ¾” – 1” clean free draining stone (type of stone varies by location);
- Compact and laser grade approximately 2” of 3/8” clean free draining stone. This is often called the finish layer; and
- Check field for planarity.
What is the purpose/function of the base?
The base generally serves to primary functions: it provides structural support to the synthetic turf surface; and, it serves to store and control storm water release in compliance with the relevant permitting agency.
How deep is the ground excavated?
Although the depth of excavation varies upon soil conditions, most fields require approximately 8” – 12” to be excavated. The excavated surface is generally referred to as the sub-grade.
What is a Proof Roll Test?
A proof roll test is used to determine whether or not the sub-grade (the surface below the stone base) will be able to structurally support the stone base and synthetic turf system so as to avoid such things as field sinking, field heaving and bases that feel inconsistent with respect to firmness, etc.
The proof roll test is typically conducted by observing whether or not a large truck (filled with stone for the base), imparts any deflection in the sub grade as it slowly rolls back and forth.
What is Soil Stabilization and when is it needed?
Soil stabilization is a means to stabilize a sub-grade that either failed the proof roll test, or, that has known “unstable” soil conditions. There are several ways to stabilize soil. The most common and cost effective ways are to mix a stabilizing material (such as kiln dried lime) into the sub-grade, or utilize a geo-grid.
What are some of the common issues with a poorly constructed base?
First, it must be pointed out that the base construction is arguably the most important part of a new synthetic turf system. Utilizing the services of a highly experienced sports field base constructor (not just someone that has only built a couple, or that builds allegedly “similar” types of bases) cannot be overstated. Problems with the base construction are the most common issues that occur with a synthetic turf system. These problems are almost always the result of inexperience and/or cutting corners with the quality of the required products and required quantities of material.
The most common issues are:
- Drainage problems with the entirety or sections of the field – this is often observed within the first year or two after construction. There are many reasons this happens. The most common are the use of stone with too many fine particles in them, overrolling/compacting the stone base, utilization of too much of the finish stone in an attempt to obtain finish grade tolerances (a common problem with inexperienced contractors);
- Flattening or heaving of sections of the field. This is typically associated with failure to remove and/or stabilize areas where deeply buried utility lines, concrete structures or organic materials existed. This issue is often observed in the spring after several freezing and thaw cycles;
- Sinking of base around perimeter of field. This is a common problem observed as a result of improper compaction methods when grading base and finish stone. This is a very common problem;
- Undulations throughout the field. This is often the result of improper compacting of stone and/or use of the wrong equipment (rollers).
Again, the use of a highly experienced base contractor cannot be over-estimated. No matter how good the quality of the synthetic turf, no matter how skilled the installers of the turf, the aesthetics, safety and performance of your turf will be compromised with a poorly constructed base.
Engineering and Permits
What type of engineering is typically required for a synthetic turf project?
The typical engineering for a new turf field includes calculations and design for proper storm water management, surveys, electrical design for such things as communication boxes, lighting and scoreboards, geotechnical engineering for soil conditions and structural engineering for such things as load bearing requirements and wind load related issues, etc.
What types of permits are generally required?
The typical permits in the Midwest include a storm water management permit, erosion control permit and a general building permit. Other permits may be required depending on the specific area where the project is located.
How long does it take to get the necessary permits?
Most permits can be obtained in less than two weeks. However, the storm water management permit can often take 6 weeks to 6 months.
How many lights are needed for sports field applications?
Although there are many variables that affect lighting quantities (including pole height, number of fixtures and lumens per fixture), a football/soccer field typically uses four light poles and a baseball field typically uses six light poles.
What are the heights of the light poles?
Typical pole heights range from 60’ – 100’. However, light pole heights vary depending on how far the poles can be set back from the area to be illuminated (and, in some cases, based on local height ordinances). The further the set-back, the higher the poles.
What are the different types of lighting systems for sports field applications?
The two lighting systems for sports field applications are incandescent lighting and LED lighting. LED lighting has a higher initial cost. However, LED lights last longer, are more energy efficient, and provide more focused and natural looking lighting with less glare. In addition, tax benefits are often available for utilizing LED lighting.