Down under: getting to the root of sub-base construction for football fields.

Synthetic surfacing companies don't agree on much, especially when it comes to the quality of the turf they manufacture. Brand A says it's better than Brand B which says it's better than Brand C.

When it comes to the importance and relevance of sub-base construction, however, they are unanimous in agreement.

"The final surface is only as good as the structure under it," says John Gilman, president of FieldTurf, the industry leader. "This is typical of most construction, be it an airport landing strip or a high-rise building. The foundation must be solid, designed for the long term. Short cuts in this regard can spell disaster--maybe not in the first year, but if shortcuts affect the playability or safety of the top surface, the consequences can be not only expensive but also dangerous."

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Without a properly engineered sub-base, the owner is playing Russian roulette. The best turf system in the world can't compensate for a poorly designed sub-base.

Gilman emphasizes that no "cookie cutter" approach works in the base design and construction of a field. Each site must be analyzed from geotechnical, drainage (rainfall and water runoff), and construction standpoints. Borings to determine the condition of the existing soils are absolutely critical. Based on these borings, plus local permitting/water management issues and local materials (available stone or sand), a properly engineered design can be developed.

"[The sub-base] is more important than the turf," says Jim Petrucelli, VP/Sales for Sprinturf. "If you don't get the base correct, if you don't get the drainage correct, we can put gold leaf turf on your field and it is never going to play right. If you don't have a solid foundation to put the turf on, it's like painting a wall. If you don't prep the wall correctly, no matter what paint you use, even if it's $100 a gallon, it's going to crack and chip and flake. It's the same with turf.

"If you don't have the right foundation, your turf will not be level. It's going to be squishy in spots and not squishy in others. It will have non-uniformity all across it, both in planarity as well as hardness, because a spot that's draining well will be much harder than a spot that is not. If you get it right, you can even place some lousy turf on top and still have a successful project."

Says Jim Savoca, national sales manager for Sportexe: "It's obviously of utmost importance. A properly constructed sub base can last several turf installations--20 or 30 years or more."

A typical time frame for sub-base construction is anywhere from 30 days to six weeks.

Before construction begins it is imperative to contact the local municipality to learn the regulations for storm water management. Almost all the major metropolitan areas have a storm management plan that tells you the rate at which you are allowed to add water to an existing storm system. In some cases, the existing storm system may be the creek that runs by the school. But you still can be restricted as to how many gallons per minute of new water you can put into that system.

A two-acre site is the size for a typical football field. On a natural grass field, depending on the soil and clay, there will be a runoff of heavy rain of anywhere from 10% to 25%. For artificial turf, the field is going to collect about 95% of the water that comes down. Depending on the storm water requirements, there could be a problem with the amount of water that is being placed into the downward system of the storm water management.

A well-designed sub-base should be able to take between 20-40 inches of water an hour. There should never be any standing water on the field--unless there is a torrential downpour in which that water will work its way into the drains--and should retain that kind of porosity for life.

Once the storm management issues have been rectified, it's time to design a sub-base that will be highly efficient and long-lasting.

Several factors are crucial to a successful project, none more so than the infrastructure. This includes "engineered dynamic stone bases, with perimeter collectors, interior drains if necessary, and generally a minimum of six inches of processed, angular stone that can be properly compacted while still draining rapidly," says FieldTurf's Gilman.

Additionally, a permeable or non-permeable geotextile fabric should be used to allow exact amounts of water to either permeate or not permeate the subgrade, depending on the existing soil. A properly designed base must have a good sieve analysis for the stone itself. It has to all fall within direct tolerances, so the stone can key together. It is advisable not to use recycled concrete or cheaper stone or a lot of crusher fines (fine crushed stone) that will provide good initial planarity, but will eventually clog the base or rut it.

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Finally, the stone base must be laser graded to ensure that the field has tolerances that are right on the money. Once that has been completed, the turf is ready to be installed.

Suffice to say, grading is crucial.

"The grade of the soil underneath, where the rock is deposited, is the most important grade on the whole field," says Grove Teates, president/owner of Alpine Services, Inc. "That grade determines where the water goes. Whether it goes to the drains or whether it doesn't. Water can lay between the drains."

Teates says his company grades more precise than anyone in the country. In fact, on a football field, he says his company we will be within a plus/minus of 8 over 450 feet, depending on the field.

"On a natural grass football field, if the sod man has done his job accurately, everybody is happy," he says. "With a synthetic field, it's exactly the same thing. The rug doesn't vary in thickness--its made on a loom. So the rug goes down accurately. The sub-base is crucial. This is evidenced by the number of artificial fields that have been built in the last five years that have been removed."

TURN TO STONE?

When it comes to base construction drainage systems, the vast majority of fields in use today are filled with stone. The introduction of a stoneless system has given schools a more cost friendly and expedient choice.

"I'm very, very encouraged by what I've seen," says Sprinturf's Jim Petrucelli.

The argument against stoneless is pretty fervent by turf manufacturers. They cite places with harsh climates, heavy rain, abundant freeze-thaw, and a lot vehicular traffic, as question marks pertaining to the durability and longevity, drainage capacity, and ability to recover from loads, not to mention safety measures, that is required of a sound turf installation.

"We know of several fields with so-called stoneless designs, fields where the school districts are paying to play at neighboring stadiums because their fields are unplayable, unfinished, and litigation brewing," says FieldTurf's John Gilman. "Experienced, reputable engineers we deal with--folks who have designed hundreds of fields on a collective basis--are not putting their reputations on the line for this kind of technology. Rather, unproven companies--trying to snag unsuspecting clients who want a field for less than $500,000--appear to be pushing this kind solution as a panacea for complex engineering challenges."

Sportexe's Jim Savoca says his company has done a limited amount of stoneless installations, but he remains skeptical.

"I know that the six-inches of crushed stone is a big, beefy investment that is going to pay dividends 20-40 years down the road," he says. "And if it isn't broke, I don't want to fix it. I know there have been some problems with them. It's a little early for us to pass judgement ... I'm just not sure this stuff with do it long-term. But the benefits are it is inexpensive and you can put it down real fast."

According to Alpine Services' Grove Teates, the key determinant's in choosing stone over stoneless is the availability and price of each product. He noted that for jobs in Colorado, stone has to be hauled a 100 miles in some cases. In South Texas, it's about 200 miles. Conversely, for a field in Somerset, NJ, the quarry was two miles away.

"I've looked hard at the six-inch stone vs the stoneless or plastic," says Teates. "The time and dollars are within 5% or less of being the same. I've done the base grading for some of those, but I don't install them yet. I've been watching closely, because it's very germane to what I do. I've not seen the plastic collars laid down perfectly flat yet. And I'm seeing some movement around the edges."

Brock USA begs to differ.

The Boulder, CO-based company has designed and engineered its Brock Performance Turf Underlayment, a stoneless impact and drainage layer, specifically for use under synthetic turf. The polypropylene bead-based material is similar to what GM uses in all its car bumpers. The 4 X 5 foot panels, which are .9 inches thick, mechanically interlock like a jigsaw puzzle, so it lays flat and doesn't slip under the turf, according to the company. An entire installation takes just two weeks.

Brock installed its first trial fields in August at Monarch High School in Louisville, CO and Centaurus H.S. in Lafayette, CO.

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"Our main goal was, 'How do you basically get rid of the stone base, and have a much simpler, faster, and more predictable installation?,'" says Brock president Dan Sawyer. "The thing with stone bases is, you never know what kind of stones you are going to get. You never know if the guy is going to level the field right. You never know if he is going to over-pack the field. There are so many unknowns.

"The whole game plan was to engineer something which meets our tag line, which is: It plays hard, it plays fast. But if you land on it, you land soft. We don't affect the playability of the field, we only affect the energy on the field."

Sawyer explained that there are many under-layers on the market that are typically products used under natural turf, but are flipped upside down and used as a drainage board underneath synthetic turf. Brock, which has been referred to as synthesize stone, is trying to bill its product as a stone alternative that results in an 80,000 square-foot tile floor that's perfectly flat, drains well and fast, and adds improvement to the overall performance of the field, while transferring its benefits to the performance and safety of the athlete.

Says Sawyer: "You can get rid of the stone in a lot of cases. You can't do that in all cases. We are not a panacea."

"The big difference is you can install a stoneless field in seven days," Sprinturf's Jim Petrucelli claims. "When you have time constraints, this works out great. You might save $30,000. That's not a lot of money. But from the standpoint of the manufacturer, if you can install a subbase in seven days as opposed to 30 days [for a stone field], obviously you can install three extra fields. The way the market is that's going to be an important factor."

ADHERING TO ADHESIVES

Once the base has been completed, the next obvious step in field design is laying the turf. Enter adhesives.

The original synthetic fields were totally glued down. Think AstroTurf, which was adhered to asphalt, with nothing in between. When companies went to the newer generation of fields, ushering in infill systems and elastic-layer padding, the usage of adhesives changed.

"The idea when you are installing an athletic field, is you want to convert those individual rolls of turf to one big piece," says Norris LeGue, president of Synthetic Surfaces, Inc., makers of Nordot Adhesives, which claims to sell more adhesive than anybody in the world that installs turf and sports and recreational surfaces. "That's done by one of two ways: sewing or gluing of the seams. Now, the only thing that keeps these seals together is the seams. If your seams aren't good, your fields aren't good. The adhesive, or the glue, becomes extremely important."

A typical gluing of a seam is as follows: adhesive is spread the width of a foot-wide piece of tape with the seam running down the middle. So the seam is glued six inches on either side.

Not everyone is in agreement that adhesives are ideal for turf installation.

"First, using adhesives should be minimized--or, better yet, eliminated," says FieldTurf's John Gilman. "We sew our turf fabric seams and always have. As a result, we don't have seam problems. Glued seams are the number one maintenance problem plaguing turf installations. In fact, we have never seen a field with glued seams that did not have seam problems, regardless of the adhesive used.

"The gluing process is just so difficult to get right--the glue is very sensitive to moisture and weather; the thickness of the glue is a factor in a successful glued seam; the amount of open time is critical and difficult to determine with exactness. Frankly, I think it's a miracle that glued seams work at all."

LeGue counters that adhesive has to have good, exterior durability anywhere in the world. It goes beyond hot and cold climates. Different scenarios such as bacteria and bugs also have to be taken into consideration.

"None of our adhesives came about by accident," says LeGue, the chemist for Monsanto that made the original adhesive to install artificial turf fields, who is known as the 'Guru of Glue.' "One adhesive won't do everything. The evolution of the past couple of years has been in developing adhesives with healing properties that fit the new turf systems that have come out. When elastic-layer was introduced, we made it possible to install and glue down elastic-layer fields with our spray system.

"When the newer, tufted turfs came out, where the stitches are protruding lower, we made an adhesive that stood up. There's one other key property that is essential called green strength, the grab of the adhesive. You need a high green strength. You want something that has an inherent initial tag to hold the surface in place when you are installing it. But not so much that you can't make a mistake in movement."

"All the components have a function," offers Jim Savoca of Sportexe. "Obviously, if you don't have a good adhesive and you're either gluing your seams or gluing your inlays down; if the adhesive doesn't hold, it's going to pop and leave an open seam and be a potential injury hazard or at the very least, a maintenance nightmare. Even though the new fields typically don't have near the glue the old fields used to have, it is very key and critical. Good adhesive is no place to skip."