The owner of a specialty infield-dirt supplier for the Houston Astros, Atlanta Braves and other baseball and softball fields needed a custom pug mill to insure a consistent product, so he went to a nearby manufacturer.

Bill Marbet, owner of Southern Athletic Fields, Columbia, Tenn., called on Pugmill Systems, also in Columbia, so he could deliver the same mix of clay and sand needed for each field—whether it’s major league, minor league, college, high school or a recreation park—every time he dispatches a truck.

“We have a formula we will put into the pug mill,” Marbet says. “We can keep a record of each customer and deliver the same thing, year after year.”

He also wanted the ability to adjust the mix of clay and sand for each client. He went to Duane Allen and John Dee Thompson, Pugmill Systems partners, to see what they could do. He outlined his needs and detailed specifications, and Pugmill’s designers went to work, making modifications to their standard to meet Marbet’s needs. Then, the manufacturers went to work.

The customized unit is shorter than most portable pug mills, designed to fit the Southern Athletic Fields trailers, said Allen, Pugmill president.

The machine provides a consistent product mix, thanks to a computer-controlled belt scale system that automatically adjusts the amounts of clay and sand added to the mix to meet the specifications for each buyer, he said.

Mounted on a trailer, the system includes a generator to power the bins, the pug mill and two conveyor sets—to the mixer and for output.

“It is really a state-of-the-art machine,” Allen said. “It mixes efficiently and controls both ingredients closely, weighing the ingredients out in the mixer.”

Engineers redesigned the standard feed hoppers to get proper material feed, especially the clay, he said.

The system, which runs at 100 tons per hour (TPH), sports 6-cu-yard and 10-cu-yd feeder bins—smaller than regular portable pug mills, which usually are configured in tandem 12-cu-yd bins or larger, said Thompson, Pugmill vice president.

“Each feeder bin has a variable-speed discharge belt and an adjustable gate,” Thompson said. “This allows the operator to get the best settings for consistent discharge.”

The computer that monitors output and automatically adjusts the mix replaces the traditional fixed rate of operation, he said.

The steel bins, manufactured on site, are lined with ultrahigh-molecular-weight (UHMW) polyethylene to improve feed-rate consistency in materials, such as clay, that tend to clog the discharge opening.

Designers added the UHMW liner to the Southern Athletic Fields system’s pug mill after early operation showed the clay was clumping and binding to the mill and shaft wall, blocking output. This is done to a few units each year, depending on their use, said Jared Allen, parts manager.

The new system also got 18-wheeler-style mud flaps—added to each side, where the mix leaves the pug mill for the conveyor belt—to prevent spillage and loss of material. The flaps can be raised to provide access to the pug mill and lowered to contain the soil mix.

The pug-mill shafts are made on site, with paddles of Nihard steel casting to resist abrasion. The paddles on the shafts are produced off site from molds designed in-house, Thompson said.

The company outsources manufacturing of trailers and larger silos for materials.

Pugmill Systems is one of a handful out of the approximately 40 pug-mill manufacturers in the U.S. that sell a complete system, Thompson said. His company’s units are “all over [the U.S.]” and in countries ranging from Chile to Japan, he said.

Thompson does not know of another company that makes a pug mill for athletic field dirt. Marbet, who started the dirt mix business in 1996, after helping maintain his sons’ Little League baseball fields, custom-blends the clay-loam soil mix to meet different teams’ needs, depending on their location. His clay-and-sand mine in northern Alabama supplies the business, which now has more than 5,000 clients. Most are situated in the South and Midwest.

Customizing the Baseball Infield Mix

The new pug mill, capable of thoroughly blending materials, is an improvement on the system of tilling a mix from a loader and bucket or blending clay and sand in a rotary drum, Marbet said. He wanted to be able to customize the mix because teams in a northern climate want a mix with more sand than teams in the South.

A custom mix can aid in percolation and also can act as a reservoir for moisture during a game. “It helps the infield soil keep its elasticity” in what Marbet calls a “cork board” effect. Dan Bergstrom, head groundskeeper for the Houston Astros for the past 13 seasons, is well acquainted with Southern Athletic Fields’ dirt mixes, having used the product before his move to Houston.

“I use Southern Athletic Fields because their products are exceptional, and the knowledge and customer service from their team is unmatched,” he said.

Baseball “is a game of consistency, and we’re looking for the same dirt every time,” Bergstrom said. “They will deliver very consistent [product] every time the truck comes in.”

That truck is an 18-wheeler that rolls in each spring in time to get the field ready for the home opener. Bergstrom allows a week for his crews to get the field ready for the season.

Keeping the field in shape “is an ongoing process,” replacing dirt caught in players’ cleats or any moved by winds, Bergstrom noted.