As just about anyone who's ever watched the Indianapolis 500 knows, a single-yard-wide set of the track's original brick surface sits exposed at the start/finish line of the famed Indianapolis Motor Speedway. But those aren't the only examples of the 3.2 million bricks laid in 1909 to be found; many are still tucked under the surface of the 2.5-mile oval asphalt track.

“Most of the bricks are still under there,” Doug Boles, IMS and INDYCAR president, tells Road & Track. “That’s the cool thing about it, when you run the Indy 500, you are racing on the same track, same layout, just a few inches above where they were in 1910 when they first started racing on the bricks.”

The Culver Blocks bricks installed back in 1909 were an effort to modernize a crushed stone and tar surface, which wasn’t performing well. The bricks—and mortar between them—remained the benchmark until the 1930s. And that’s when historical layers started transforming the home of the Indy 500.

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Changes Over Time

The first real asphalt came to The Brickyard in the 1930s, when the track added it in the corners. Then, in 1939, the track laid asphalt on the back stretch. The 600-yard front stretch remained brick until 1961; After A.J. Foyt won that year's race, asphalt took over the front stretch for the first time, except for that single yard of bricks that remains today.

The next major resurfacing came in 1976 — a laying of asphalt atop the existing surface and the first complete redo of the track since the addition of bricks in 1909. The 15-year gap between resurfacings was then shortened to 12 years, when a new asphalt layer was added in 1988. Seven years later, in 1995, came a project that removed five inches from the surface — the first time any was removed during the resurfacing — and put down a new asphalt layer. In 2002, the track received a diamond grinding to smooth the surface; 2004 brought an entire resurfacing and the removal of about 2.5 inches of old asphalt. That was the last time the track was completely redone, although in 2005 another diamond grinding session removed undulations and smoothed the track to increase grip, especially in the corners.

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“It's hard to believe this is the twenty-first season of this asphalt,” Boles says, adding this is the longest stretch since 1961 the track has gone without a resurfacing.

A core sample taken from the exit of turn three in 2017, where a crack had developed, showed everything from the bricks all the way up to the differing layers of asphalt. “To see it all in this 18-inch-tall, six-inch-diameter core sample was unbelievably powerful,” Boles says. “The bricks are there.”

The Special Recipe

The first asphalt used in the 1930s included a type known as "Kentucky Slag." The same firm that lays asphalt at the IMS now is a descendant of the company that did the work nearly 100 years ago, and still uses pieces of the same asphalt recipe introduced back then — but with modifications.

The Brickyard diagram of concrete and bricks

The slag, which features steel as the unique component, is a key bonding agent, Boles says; this enables an improved grip level out of the relatively flat oval of 9 degrees, 12 minutes. The changes to the asphalt recipe over time — it's a special combination used specifically for the IMS — are to ensure it can handle the 140 days of racing that now occurs on the track, including the NASCAR Cup cars that weight 3500 pounds versus the the 1600 lbs of an Indy car.

Boles says drivers offer mixed responses as to if the track should be resurfaced again, but other parts of race teams have a desire to wait as long as possible. “Team engineers say ‘No,’ because it is a surface they know,” Boles says. “There will be a day we have to, but then they will have to start completely over with new grip levels. Now it is one thing that is not a factor when determining the car setup because people just know it.”

Modern-Day Maintenance

The grip level is a key piece of information for racing teams. The IMS performs a friction test three times a year, with the most important in the spring, to report the grip to teams. (The procedure started because drivers were spinning out in the warmup lanes, and a friction test showed the track wasn't as grippy in those areas.) “Over the last few years, it has gotten slightly better over winter to summer just from the sun,” Boles says. “It stays pretty standard year after year.”

Modern-day maintenance is sparse, though, as the IMS lets nature run its course. Boles calls the surface “sort of this living, breathing thing,” and “the thing we pay the most attention to.”

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At no point is the track covered from the elements, never plowed and no chemicals are put on it. “We basically leave the track surface alone,” Boles says. “We felt the best process is to let it do its thing.”

What officials do worry about, though, is water seeping through and creating a freeze-thaw process in the underlying layers, especially at the brick level. As the bricks and mortar expand and contract in the subsurface, it can create unevenness at the surface. So the IMS team measures the entire surface to track any movement.

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Since the bricks and mortar cycles through the freeze-thaw cycle at a different rate than the asphalt, issues can arise. This year, the team found that the exit of turn two was two-tenths of an inch higher than it was in 2024. Crews rolled it out, and now it's back in line.

“Sometimes you’ll find [issues] because some areas might still be frozen and others not, so you might see imperfections,” Boles says, “but it flattens itself back out once the full thaw happens.”

Roughly every three years, IMS adds a rapid penetration emulsion designed to penetrate the track. It isn’t a coating, but is intended to fill microscopic holes under the surface that could hold water. At times, the team will have to fill cracks — such as one that runs parallel to the drivers’ left inside of each of the four corners where, after the 2004 resurface, the first lane separated from the upper lanes. “We literally take ketchup bottles and hand-seal with a compound to keep water from going down in it,” Boles says. “Water is our enemy. We are trying to do anything we can not to allow more water into it.”

Core samples help tell the story of the track's history, but they also can help IMS understand modern-day issues. In 2017, a backstretch concern — drivers noticed two bumps — showed that some places were missing a row of brick. Boles said that in the 1930s, when a freeze-thaw cycle happened and bricks buckled under the temperature change, officials would remove rows of bricks and fill the void with asphalt. Other than those few areas, however the bricks remain under the Brickyard's skin.