Technically, the term infield skin refers to segments of the baseball field that contain clay, specifically the areas around the bases and base paths. The keys to quality infield skin are good materials, proper moisture and consistent maintenance practices. With 70 percent of the game played on the infield, having a consistently firm, smooth playing surface is essential.
Infield mixes are made from various combinations and percentages of sand, silt and clay. People consider the general standard for an OK infield to be 60 to 70 percent sand, 30 percent clay and 10 percent silt. Particle size also makes a big difference in these materials. Infields vary greatly by regional conditions, commercially available mixes and the preferences of the sports field manager and their facility and teams.
The weight of the infield mix is in the clay and the silt and that’s what retains the moisture. You may be in an area with a lot of rain, and if you don’t have much maintenance help for tarping you’ll want to have a bit sandier infield mix. If you have a heavily used field or one for university or professional play, you’ll probably want a more stable infield with a heavier mix containing more clay and silt to withstand the wear and tear of multiple events. For some infield mixes with lesser percentages of silt and clay, a conditioning amendment of calcined or vitrified clay is worked into the top 1 to 2 inches of the mix to help bind the clay and stabilize the infield.
When constructing a new field or rebuilding an existing one, the general depth of the infield material for the baselines is approximately 5 inches. The depth, the type of material used and the subbase components are subject to budgetary constraints. There are fields with the infield mix placed directly on the subbase soil, some on a sand layer over the subbase soil, some directly on a pea gravel layer and some on geo cloth covering any of these subbases.
Opinions differ on whether a geo cloth layer will be detrimental to drainage. While drainage within the infield mix will vary according to the percentages of clay and silt, it is generally slow, so many prefer the geo layer for other advantages. It can keep pea gravel from migrating up into the infield mix and bordering grassed areas. Geo cloth on the pea gravel does keep the infield mix from sifting into the gravel, reducing the need for continual addition of the mix during the first few years of construction and helping stabilize the surface more quickly.
To counteract slow drainage within the infield mix, many fields are constructed with a slope to help move the surface water off the clay and into the grass. A slope of about .5 percent, extending from the edge of the pitcher’s mound out past the 95 arc should provide sufficient water movement for most fields. Some skinned baseball infields and some softball fields are constructed with a greater percentage of slope.
It’s critical to achieve consistency of slope across the entire surface. Use laser-grading equipment and a skilled operator. Otherwise, once all the material is in place, run string lines from the infield grass to the outfield grass across the infield and work your way across the field with shovels and rakes. Keep moving the string lines every 1 to 2 feet, and check and recheck for accuracy as you move.
An inground irrigation system with a zone that only waters the infield clay is one way to deliver volumes of water quickly. When water patterns are diverted in windy conditions, hand-watering will be required to reach the places missed.
Quick-connect outlets behind the mound and behind home plate provide access to hook up a water hose. Some field managers place quick couplers at the infield corners behind first and third base in the grass. A 1-inch hose is preferred to deliver a larger volume of water faster. A retractable hose reel installed in the ground behind the mound makes pull out and rollback easier and eliminates hauling the hose out and back for each watering.
Select hoses and hand-nozzle sizes based on the number of fields you need to maintain and the size of your crew. Ideally, your nozzle selection should be able to apply enough water to reach the desired depth for the initial soaking and to lightly mist repeatedly to maintain the desired moisture level. Some infields drain so well that you can “puddle” the infield after a night game and it will be perfect for play by morning.
Top it off
Using the different calcined or vitrified clay amendments as the top surface coat can make it a little easier to manage the skin moisture levels and achieve consistency. You don’t want the players to pick up wet clay on their spikes or have the infield get too dry during the pregame workouts. With a topping of 1/8 to .25-inch, you can soak the infield as you would normally and have a good surface for workouts and sufficient moisture retention for the game. Consistency of depth is extremely important during the initial application of the top layer both for accuracy of the slope and footing for the players. Once in place, use a cocoa mat or the back of a fan rake so you’re just lightly smoothing the top surface and not moving piles of material.
An infield tarp is an important tool in moisture management. No one likes to use it, but covering the infield when you have rain issues can be the quickest and easiest way to preserve playability.
The worst thing you can do following a heavy rain on an uncovered field is to work the field too early. Let the sun do its work on the dry down before you get out there to squeegee, rake and dig. The dryer subsurface material will try to draw down the moisture from an undisturbed wet surface. If you must work existing or added material to dry down the surface, use a roller squeegee rather than a rake to spread the water so you’re not cutting into the wet material and disrupting that downward movement.
If you have depressions with standing water, fill them with calcined clay and let it soak up the moisture for 15 to 20 minutes. Then, spread out that moist material to dry further, or borrow a technique from ground crews in South America to remove excess water with no surface penetration. They use a supply of 12-by-24-inch foam-rubber sponges (old padding) and place one in an area of standing water, step down on it, allow it to absorb water to capacity, pick it up, wring it out and use it again.
Another technique to combat light rain or drizzle, and to use between innings when the dirt is starting to look shiny, is to apply a very thin layer of conditioner using a regular walk-behind or hand-held spreader set for the largest opening. You’ll get a more consistent layer than pouring conditioner from the bag or putting out piles to spread.
Working the dirt
The right equipment used properly is critical in maintaining the infield skin. You’ll want a series of different types of drag mats, rigid and flexible steel mats for breaking up dirt clods and leveling, and cocoa mats for finishing the surface. You’ll need both a fine nail and heavy nail drag for scarifying the surface and digging deeper to further loosen the mix and allow better moisture penetration. You’ll need rakes, brooms, edgers and rollers. The 1 or 2-ton roller will become your favorite tool.
The three-wheel field rakes produced by the major equipment suppliers do an excellent job, and they come with an assortment of attachments, as well as connection points for other implements. You also can use a small tractor, lawn mower, utility vehicle or golf cart to pull the drags.
Always pull the bases and insert the plugs so you can drag the entire infield. Pay close attention to the wear areas around and in front of the bases, such as where the first baseman plants his foot. Consider incorporating a heavier clay mix 10 feet out from first base and also at second and third base to make it easier to reduce divoting and keep indentations from forming. Follow different routes when driving equipment onto the field to reduce compaction issues. Transport the drags to the field and drop them at different spots each day. When working the field, keep attachments, drags and screens 6 inches away from the grass at both edges of the base path to avoid lip build up. Use a variety of dragging techniques, continually altering your patterns and incorporating circular spirals and figure eights. Go slow, especially in the turns, to avoid slinging materials.
To avoid creating lips when hand-raking, always rake up and down the base path, not across it. Work the grass edges with a fan rake or stiff-bristled broom after every practice, workout and game. If you don’t have the staff for that, use the water hose to blast the infield mix from the grass edges at least once a week.
You’ll want to edge the infield grass periodically, cutting away turf to remove any lip buildup, then backfill with new infield mix, tamp down firmly and test the edge. There should be no transition between the grass and the clay. If you can feel even the slightest difference with your foot, the ball can feel it when it hits, and that’s what causes a bad hop.
Murray Cook is president of Brickman Sports Turf Services, a division of the Brickman Group. He’s a frequent overseas traveler on behalf of Major League Baseball and the International Baseball Federation.