The Better Billy Bunker Method: How Bridging Stone, Polymer, and Sand Work Together

The Better Billy Bunker (BBB) method is a polymer-bonded gravel bunker liner system that combines a 2-inch drainage layer of pea gravel, a sprayed polymer binder that cures into a flexible porous mat, and a 4-inch compacted sand layer above. The system drains water faster than 2,500 inches per hour, prevents fines migration from the underlying soil into the bunker sand, and reduces washouts during heavy rain. BBB has become one of the two dominant bunker liner choices for new construction and renovation in the U.S., alongside porous-concrete systems. This guide explains how the method works, what bridging stone specifications matter, where the BBB system fits relative to other liner options, and how superintendents decide which approach is right for their site.

What Is the Better Billy Bunker Method?

BBB is a linerless drainage system. There is no fabric layer between the soil and the sand. Instead, the drainage role is played by a polymer-coated gravel layer that doubles as the structural barrier. The approach was patented and commercialized in the late 2000s and is licensed through Better Billy Bunker LLC. Authorized installers across North America build the system as a turnkey package: site prep, gravel placement, polymer spray application, cure time, and final sand fill.

The result is a smooth, slightly flexible drainage surface beneath the bunker sand that lets water move vertically into the perimeter drain tile without taking the sand with it. Because the polymer cures to a porous-but-bound mat, the gravel does not wash up into the sand during heavy rain events, which is the most common failure mode for traditional fabric-lined or unlined bunkers.

How the Layers Work, Step by Step

1. Excavate a 6-inch profile across the bunker floor. Grade with the perimeter or sub-surface drain tile so water has a downhill path to exit the bunker once it passes through the gravel.
2. Place a 2-inch layer of approved bridging gravel across the entire bunker floor. The original BBB spec calls for gravel sized 3/16-inch to 1/4-inch (4.5 to 6 mm). Some renovation specs use a slightly coarser USGA-style bridging stone in the 1/4-inch to 3/8-inch range. The architect or BBB-licensed installer will specify the exact gradation for the site.
3. Spray the proprietary polymer (ST410) over the gravel. The polymer seeps down through the gravel matrix and cures into a flexible porous mat that locks the stones together while preserving the void space needed for drainage.
4. Allow the polymer to cure per the installer's schedule. Cure time depends on ambient temperature and humidity but typically falls in the 24 to 48 hour range.
5. Install the bunker sand. The tested and approved bunker sand is placed at a minimum 4-inch compacted depth and finish-graded. The bunker is now ready for play.

Why Bridging Stone Specs Matter

Bridging is a USGA term for the relationship between the drainage gravel and the rootzone or sand above it. When sized correctly, the gravel particles are large enough to drain freely yet small enough that the sand above bridges across the void spaces and does not migrate down. USGA guidance for putting green construction calls for at least 65 percent of gravel particles to fall between 1/4-inch (6 mm) and 3/8-inch (9 mm), and for the gravel uniformity coefficient (D90 / D15) to be 2.5 or less. The bridging factor itself, gravel D15 no greater than five times rootzone D85, is the rule that prevents fines migration.

For BBB-method bunkers, the polymer locks the gravel layer in place so the geometric bridging requirement is less load-bearing than in a USGA green build, but particle size still matters for drainage rate and for compatibility with the sand placed above. Working from a known, USGA-tested gravel source removes a variable from the install. Thelen Golf & Sports supplies USGA 3/8-inch Bridging Gravel and IDOT CA7 spec aggregate for bunker drainage work, and partners with course architects, builders, and installers to match the right bridging stone to the specified liner system.

Better Billy Bunker vs. Other Liner Systems

BBB is one of two porous-aggregate liner systems that dominate bunker construction today. The other major option is porous concrete (CapillaryFlow / Capillary Bunkers), a homogeneous 2-inch concrete mat installed across the bunker floor. Both systems target the same problem: stop washouts, stop fines migration, and deliver predictable drainage. They differ in install method and cure profile.

BBB uses locally available pea gravel that gets bound on site by the proprietary polymer spray. The cured system retains some flexibility and tends to follow the contoured shape of the bunker floor closely. Porous concrete arrives as a pre-mixed pour that sets up rigid; it provides a more uniform 2-inch layer once cured. Drainage rates are comparable in published claims, both systems quoting roughly 2,500 inches per hour.

Choosing between them comes down to construction-phase logistics, the architect's aesthetic and renovation intent, regional installer availability, and budget. The good news for superintendents is that both systems rely on the same upstream supply chain for the bunker sand placed above, and a properly specified bunker sand from a tested source like Thelen's Diamond or Double Diamond Bunker Sand performs well over either liner.

When Course Operators Should Consider a BBB Renovation

• Bunkers are washing out in heavy rain events, requiring crew time to push sand back in place after every storm.
• Sand contamination is accelerating because fines from the underlying soil are migrating up through the existing fabric or unlined floor.
• Drainage tile is in place but bunker sand stays soggy after rain, suggesting the layer above the tile is not moving water effectively.
• Master plan calls for a refresh of bunker shapes, edges, or sand specification, and the floor work can be combined with the sand swap for cost efficiency.
• Course is preparing for a tournament, championship, or aerial-photography moment that demands consistent bunker presentation.

Frequently Asked Questions

What is the Better Billy Bunker drainage system?

It is a polymer-bonded gravel bunker liner that combines a 2-inch layer of pea gravel coated with a sprayed polymer binder and a 4-inch compacted sand layer on top. The cured polymer holds the gravel together while preserving void space, allowing water to drain at rates exceeding 2,500 inches per hour without sand washouts.

What size gravel is used in a Better Billy Bunker?

The original BBB specification calls for gravel sized 3/16-inch to 1/4-inch (4.5 to 6 mm). Some renovation and site-specific specs use a slightly larger 1/4-inch to 3/8-inch USGA-style bridging stone. The BBB-licensed installer or course architect specifies the exact gradation for each project.

What is USGA bridging stone?

Bridging stone is drainage gravel sized to the USGA specification for putting green and bunker drainage construction. USGA guidance calls for at least 65 percent of particles to fall between 1/4-inch (6 mm) and 3/8-inch (9 mm), with a uniformity coefficient (D90 / D15) of 2.5 or less. The size and shape are designed to bridge against the sand layer above without allowing fines to migrate down or sand to fall through.

How long does a Better Billy Bunker installation take?

Excavation, gravel placement, polymer spray, and cure typically span three to five days per bunker, with cure time of roughly 24 to 48 hours depending on temperature and humidity. Sand fill follows immediately after cure. Crews on a renovation project often run multiple bunkers in parallel to shorten the overall project timeline.

How does Better Billy Bunker compare to porous concrete liners?

Both systems target washouts, fines migration, and predictable drainage, with comparable drainage rates in published claims. BBB uses on-site polymer-bound gravel and stays slightly flexible after cure. Porous concrete (CapillaryFlow / Capillary Bunkers) is a pre-mixed pour that cures rigid into a uniform 2-inch mat. Choice depends on construction-phase logistics, architect intent, regional installer availability, and budget.

Where can I source the bridging stone and bunker sand for a BBB project in the Midwest?

Thelen Golf & Sports supplies USGA 3/8-inch Bridging Gravel, IDOT CA7 aggregate, and tested Diamond and Double Diamond Bunker Sand to courses across Illinois, Wisconsin, Iowa, and the broader Midwest. Project experience includes Erin Hills, The Club at Strawberry Creek, and Heritage Bluffs Golf Club. The team coordinates directly with course architects, builders, and BBB-licensed installers on material sourcing and delivery.

Talk to Thelen About Your Bunker Renovation

Thelen Golf & Sports has supplied bunker sand, bridging stone, topdressing, and construction mixes to golf courses across the Midwest since 1947. The team works directly with superintendents, course architects, and renovation builders to spec the right materials for the chosen liner system, schedule deliveries to match construction windows, and confirm that the sand specified above the liner is compatible with site rainfall, play volume, and tournament expectations.

Browse the full product list to see bunker, drainage, and construction-mix options.

Request a quote or talk to Joe Velasco or Owen Petray about your bunker project.

Review project case studies including Erin Hills, The Club at Strawberry Creek, and Heritage Bluffs Golf Club.