Force Reduction on Tennis Court Surfaces
NGI Sports specializes in surfaces that provide optimum playability and cushioning properties. At NGI Sports material science is becoming one of the largest areas for innovation in tennis surface engineering and technology. Force reduction through cushioning and shock attenuation is not only an important property of a tennis court surface, it is also considered a key indicator of the performance, safety, comfort, and suitability of the surface for play.
A tennis player’s lower body is subject great stress and abuse through movements that create different forces on the lower extremities. Rapid stopping or foot planting creates some of the highest forces in tennis. There are frequent center of gravity adjustments where the body's center of gravity needs to be adjusted in any direction quickly and in a controlled manner, the direction of the forces placed on the foot and leg are forward, backwards, vertical as well as lateral. The body encounters more than just its own weight worth of forces from the energy returned from the tennis court. The surface therefore is important in reducing the impact of those forces to your lower leg and back.
As a designer and manufacturer of tennis court surfaces we use impact tests to measure and evaluate the effects surfacing design and surface design changes have on the impact forces generated on the body from the surface.
Testing results assist owners and players in making an informed, efficient, and empirical decision concerning a replacement tennis surface and for decisions regarding new surface selection. Puhulla et al (1999) defines hardness as “the ability of the surface to absorb shock imparted by the colliding object”. The most promising piece of equipment to measure surface hardness in the field is the Clegg Impact Hammer ®. This apparatus is an accelerometer device that relates to the deceleration of a falling weight on impact (Sifers and Beard, 1992; Neylan et al 1998).
We have conducted impact tests on numerous court surfaces. The impact forces simulated in the test method are intended to represent those produced by the lower extremities of a tennis player during play and impact on the tennis court. The Clegg machine fitted with electronic sensing instrumentation. Results are expressed in G Max values from 100 to 500. Benchmark figures for our use were based on concrete, asphalt and clay pavements.
In most cases clay (fast-dry) court play on courts two (2) to six (6) years old is thought to provide for a very comfortable and forgiving surface. Of course, the slide or foot release factor is not considered in this test. Results are based on an average of numerous sites tested with varying site conditions. Note that a larger numerical value reported represents less force reduction, a surface harder on the body.
|Post Tension Concrete color only||732|
|Concrete slab tennis court with filler coats & acrylic color||495.1|
|Asphalt tennis court with acrylic color||334.3|
|Fast-Dry tennis court (4 yrs old)||244.6|
|Fast-Dry tennis court (8+ yrs old)||327|
|ProBounce all weather surface||245.3 (over cracked asphalt, 8 years old)|
|ProClay Tennis Court Surface||181.1 (over crushed stone base, 6 years old)|
|ProCourt XP (Granule In-filled Synthetic Turf Court)||132.4 (over cracked asphalt, 6months old)|
|ProXtreme (Urethane Cushioned Court)||249.5 (over cracked asphalt, 1 year old)|
|TitanTrax Shield with DecoTurf Cushion||292.1 (over concrete slab)|
|NOVA’PRO SURFACE||PERCENTAGE OF GREATER FORCE REDUCTION FOR NGI SPORTS' SURFACE AS COMPARED TO CONCRETE|
|THE NUMBERS INDICATE THE % IMPROVEMENT IN FORCE REDUCTION OF THE NOVA’PRO SURFACE AS COMPARED TO THE COURT SURFACE|
These tests indicate a significant decrease in stress or advantage in force reduction for the NGI Surfaces. This appears true in all cases when compared to tennis courts built with hard pavement; thin cushioned finishes and as good as or better than clay courts in good condition.
We are continuing this study to build a database that compares the most prevalent courts in use today.
Birdbaths, depressions, or low areas on tennis courts are commonly defined as a low spot on the court that holds water. According to the ASBA (www.sportsbuilders.org), a birdbath is any area that water gathers and is held in a volume higher than 1/16” (2mm or the width of a nickel) for longer than an hour of drying in 70 degree Fahrenheit.
Depending on the severity of these areas, they could lead to delayed play and in the longer run mold or algae. The mold is a greater concern as it can either make play unsafe due to slick conditions, and even delaminate the acrylic on the surface. It is generally recommended to keep any court clean of such growth; power washing the courts is an effective action for mold removal.
These depressions could also be a result from improper construction or base preparation. Meaning that the courts could have been constructed using an improper slope, organic materials in the subsoil, improper compaction of the sub grade, or even bad drainage around the site. Over enough time most courts “settle” even with a perfect installation because of materials in the subgrade or site drainage issues.
There are 3 ready solutions for birdbaths, and they range in application and price. The cheapest option would be to apply multiple coats of an acrylic patch mix, once built up and flush with the surrounding areas and sanded smooth the courts could be painted. Next, you could tear out the court, or re-mill the asphalt giving a new surface. One of the most effective options would be to employ a modern day synthetic overlay system; they range in style, cost, and construction, but may also be the most cost effective. Depending on the court and its condition.
Give your surface a fighting chance; place the emphasis on the preparation!
Prep work is the foundation for successful performance of any sports surface, especially Tennis Courts. Properly preparing the existing surface (base) before it receives any type of new overlay or even just acrylic paint should be common sense. Surprisingly, many problems arise from this lack of attention to detail. A proper foundation is paramount for building any sort of structure. Most surfacing problems arise from improper base preparation.
Which leads us to the question; what is an acceptable level of preparation? The manual for the American Sports Builders Association will tell you that for asphalt surfacing that filling any birdbaths deeper than the width of a nickel and all cracks with an acceptable blend of a concrete latex patch mix is acceptable. If the cracks are wider than an inch and a half and seem to run all the way through the base; then filling with sand, concrete, and then a latex patch mix is the standard. This is a generally accepted method for crack filling, and once sanded smooth the surface is ready for acrylic. So why should anyone expect anything less than these standards for an overlay system?
A rule of thumb for all overlay systems, ranging from cushioned all weather courts to synthetic grass court, is that abnormalities in the base will reflect through to the surface. Depressions will not be hidden by placing another surface on top, and any gaps left in the existing base may translate either by being cosmetically visible or producing less than standard ball bounce (dead spots). The “prep work” section of a tennis construction proposal just may be the most important part. So, make sure your surface preparation is perfect and give your tennis court a chance to perform as designed.
More information about cracks.
For more information on crack filling read the Opinion Line titled Crack Filling 101 from a 2008 edition of the American Sports Builders Association
Why do asphalt tennis courts crack?
There isn’t a singular exclusive reason for the cause of cracking on a hard asphalt tennis court, but there are a few significant factors that play a role in the deterioration of the court.
Causes for cracking in asphalt courts vary regionally. The quality and the composition of the asphalt mix can definitely be a factor. In previous years the court contractor would have been able to customize the mix design for a tennis court. Today the contractor is at the mercy of the (asphalt) plant, and what they are running as their day-to-day “mix”. Which most likely is for use in roads and highways. The amount of AC (asphalt cement) in the mix today is much less than in previous decades, and todays base processors that lessen the quality of the AC have compromised asphalt quality. This means asphalt pavement dries out and oxidizes rather quickly becoming brittle over time and makes it more susceptible to damage from weather conditions such as freeze/thaw, temperature shifts, and ground moisture or drought.
A tennis court is only as good as its base, but over enough time all asphalt courts will eventually deteriorate. It really just becomes a questions as to the severity of the damage.
So, preventative action consisting of choosing a good site, quality contractor, and correct surface for your needs, becomes invaluable. Reputable contractors can be found through the ASBA (www.sportsbuilders.org). If cracking does occur and the courts become unplayable, there are alternatives to removing the existing surface, such as overlay systems (www.ngisports.com). Professionals are available there to help with all of your tennis court needs.