The short answer: to level a street bench on uneven pavement without shims, adjust the bench itself or its mounting point. Shims tend to slip, trap moisture, and look like a temporary bodge. Here are the methods I use when a bench rocks on an old sidewalk or asphalt.
First, find the actual problem. Place a spirit level on the seat front-to-back and side-to-side. Rock the bench by hand. If it rocks diagonally, two opposite legs are high. If it wobbles side-to-side, one end is high. Measure the gap under the floating leg with a feeler gauge, coins, or a stack of washers—just for measurement, not as a permanent fix.
Method 1: Install adjustable bench feet. This is the cleanest solution. Many street benches have holes or plastic inserts at the bottom of the legs. Pop out the plastic cap and check for threads. If there are threads, screw in a stainless steel leveling foot or furniture glide with a threaded stud. If there are no threads, drill a pilot hole and install a T-nut in wood or a threaded rivet nut in metal. Then turn the foot in or out until the bubble on your level is centered. Once it is right, tighten the lock nut against the leg. This gives you a solid, hidden adjustment point and makes future releveling easy.
Method 2: Trim or grind the long leg. If adjustable feet are not an option, mark the high leg with masking tape. Remove the bench or flip it carefully. For metal legs, cut along the tape line with an angle grinder and a cutoff wheel, or use a hacksaw for smaller tube. For wood legs, use a handsaw or oscillating multi-tool. Cut in small increments—about 1/8 inch at a time—then set the bench back down and check with the level. It is much easier to take off a little more than to add material back. After trimming metal, seal the raw edge with cold galvanizing spray or rust-resistant paint. For wood, apply a waterproof sealer so the end grain does not soak up water.
Method 3: Recess the high side into the pavement. This works well when you maintain the surface and cannot modify the bench, such as with some heritage or powder-coated frames. Mark the footprint of the high leg on the concrete or asphalt. Use a masonry grinding cup on an angle grinder to remove a shallow pocket. Work slowly, stop frequently, and test the fit. Keep the recess as small as possible and avoid cutting through the surface into the base. On asphalt, you can sometimes heat the area with a torch and press the leg down slightly, but that is messier and best left to a paving contractor.
Method 4: Anchor with adjustable hardware. For a permanent installation, drill holes through the bench feet or use surface-mount brackets. Drop-in anchors or wedge anchors in concrete can hold a threaded rod. Thread a nut and washer onto the rod, set the bench foot on top, and add another nut above. By adjusting the lower nut, you raise or lower that corner. Tighten the upper nut to lock the leg. This is not a shim; it is an engineered adjustable connection that also keeps the bench from walking or being stolen.
Method 5: Reposition the bench. Sometimes the pavement is too far out of level to fix cleanly. If you can rotate the bench a few degrees or move it a few feet, the four legs may land on a flatter plane. This is the least invasive option for public sidewalks and rental properties.
A few things to avoid: do not stack roofing felt, cardboard, or plastic scraps under the leg. They compress, trap water, and eventually spit out. Also do not grind public pavement without checking local rules or ownership—many municipalities treat sidewalk surfaces as public infrastructure.
Whichever method you choose, go back after a week and check the level again. Pavement settles, wood swells, and hardware can loosen. A stable bench is not a one-time fix; it is a small maintenance habit.